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Ticket #5368: allow-dot.patch

File allow-dot.patch, 168.2 KB (added by Amit Upadhyay <upadhyay@…>, 17 years ago)
fix and documentation update.

django/core/validators.py

 integer_re = re.compile(r'^-?\d+$')
 ip4_re = re.compile(r'^(25[0-5]|2[0-4]\d|[0-1]?\d?\d)(\.(25[0-5]|2[0-4]\d|[0-1]?\d?\d)){3}$')
 phone_re = re.compile(r'^[A-PR-Y0-9]{3}-[A-PR-Y0-9]{3}-[A-PR-Y0-9]{4}$', re.IGNORECASE)
 slug_re = re.compile(r'^[-\w]+$')
+slug_re = re.compile(r'^[-\w\.]+$')
 url_re = re.compile(r'^https?://\S+$')
 lazy_inter = lazy(lambda a,b: force_unicode(a) % b, unicode)

docs/model-api.txt

 ===============
 Model reference
 ===============
 A model is the single, definitive source of data about your data. It contains
 the essential fields and behaviors of the data you're storing. Generally, each
 model maps to a single database table.
 The basics:
     * Each model is a Python class that subclasses ``django.db.models.Model``.
     * Each attribute of the model represents a database field.
     * Model metadata (non-field information) goes in an inner class named
       ``Meta``.
     * Metadata used for Django's admin site goes into an inner class named
       ``Admin``.
     * With all of this, Django gives you an automatically-generated
       database-access API, which is explained in the `Database API reference`_.
 A companion to this document is the `official repository of model examples`_.
 (In the Django source distribution, these examples are in the
 ``tests/modeltests`` directory.)
 .. _Database API reference: ../db-api/
 .. _official repository of model examples: ../models/
 Quick example
 =============
 This example model defines a ``Person``, which has a ``first_name`` and
 ``last_name``::
     from django.db import models
     class Person(models.Model):
         first_name = models.CharField(max_length=30)
         last_name = models.CharField(max_length=30)
 ``first_name`` and ``last_name`` are *fields* of the model. Each field is
 specified as a class attribute, and each attribute maps to a database column.
 The above ``Person`` model would create a database table like this::
     CREATE TABLE myapp_person (
         "id" serial NOT NULL PRIMARY KEY,
         "first_name" varchar(30) NOT NULL,
         "last_name" varchar(30) NOT NULL
     );
 Some technical notes:
     * The name of the table, ``myapp_person``, is automatically derived from
       some model metadata but can be overridden. See _`Table names` below.
     * An ``id`` field is added automatically, but this behavior can be
       overriden. See `Automatic primary key fields`_ below.
     * The ``CREATE TABLE`` SQL in this example is formatted using PostgreSQL
       syntax, but it's worth noting Django uses SQL tailored to the database
       backend specified in your `settings file`_.
 .. _settings file: ../settings/
 Fields
 ======
 The most important part of a model -- and the only required part of a model --
 is the list of database fields it defines. Fields are specified by class
 attributes.
 Example::
     class Musician(models.Model):
         first_name = models.CharField(max_length=50)
         last_name = models.CharField(max_length=50)
         instrument = models.CharField(max_length=100)
     class Album(models.Model):
         artist = models.ForeignKey(Musician)
         name = models.CharField(max_length=100)
         release_date = models.DateField()
         num_stars = models.IntegerField()
 Field name restrictions
 -----------------------
 Django places only two restrictions on model field names:
 . A field name cannot be a Python reserved word, because that would result
        in a Python syntax error. For example::
            class Example(models.Model):
                pass = models.IntegerField() # 'pass' is a reserved word!
 . A field name cannot contain more than one underscore in a row, due to
        the way Django's query lookup syntax works. For example::
            class Example(models.Model):
                foo__bar = models.IntegerField() # 'foo__bar' has two underscores!
 These limitations can be worked around, though, because your field name doesn't
 necessarily have to match your database column name. See `db_column`_ below.
 SQL reserved words, such as ``join``, ``where`` or ``select``, *are* allowed as
 model field names, because Django escapes all database table names and column
 names in every underlying SQL query. It uses the quoting syntax of your
 particular database engine.
 Field types
 -----------
 Each field in your model should be an instance of the appropriate ``Field``
 class. Django uses the field class types to determine a few things:
     * The database column type (e.g. ``INTEGER``, ``VARCHAR``).
     * The widget to use in Django's admin interface, if you care to use it
       (e.g. ``<input type="text">``, ``<select>``).
     * The minimal validation requirements, used in Django's admin and in
       manipulators.
 Here are all available field types:
 ``AutoField``
 ~~~~~~~~~~~~~
 An ``IntegerField`` that automatically increments according to available IDs.
 You usually won't need to use this directly; a primary key field will
 automatically be added to your model if you don't specify otherwise. See
 `Automatic primary key fields`_.
 ``BooleanField``
 ~~~~~~~~~~~~~~~~
 A true/false field.
 The admin represents this as a checkbox.
 ``CharField``
 ~~~~~~~~~~~~~
 A string field, for small- to large-sized strings.
 For large amounts of text, use ``TextField``.
 The admin represents this as an ``<input type="text">`` (a single-line input).
 ``CharField`` has an extra required argument, ``max_length``, the maximum length
 (in characters) of the field. The max_length is enforced at the database level
 and in Django's validation.
 Django veterans: Note that the argument is now called ``max_length`` to
 provide consistency throughout Django. There is full legacy support for
 the old ``maxlength`` argument, but ``max_length`` is prefered.
 ``CommaSeparatedIntegerField``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 A field of integers separated by commas. As in ``CharField``, the ``max_length``
 argument is required.
 ``DateField``
 ~~~~~~~~~~~~~
 A date field. Has a few extra optional arguments:
     ======================  ===================================================
     Argument                Description
     ======================  ===================================================
     ``auto_now``            Automatically set the field to now every time the
                             object is saved. Useful for "last-modified"
                             timestamps. Note that the current date is *always*
                             used; it's not just a default value that you can
                             override.
     ``auto_now_add``        Automatically set the field to now when the object
                             is first created. Useful for creation of
                             timestamps. Note that the current date is *always*
                             used; it's not just a default value that you can
                             override.
     ======================  ===================================================
 The admin represents this as an ``<input type="text">`` with a JavaScript
 calendar and a shortcut for "Today."
 ``DateTimeField``
 ~~~~~~~~~~~~~~~~~
 A date and time field. Takes the same extra options as ``DateField``.
 The admin represents this as two ``<input type="text">`` fields, with
 JavaScript shortcuts.
 ``DecimalField``
 ~~~~~~~~~~~~~~~~
 **New in Django development version**
 A fixed-precision decimal number, represented in Python by a ``Decimal`` instance.
 Has two **required** arguments:
     ======================  ===================================================
     Argument                Description
     ======================  ===================================================
     ``max_digits``          The maximum number of digits allowed in the number.
     ``decimal_places``      The number of decimal places to store with the
                             number.
     ======================  ===================================================
 For example, to store numbers up to 999 with a resolution of 2 decimal places,
 you'd use::
     models.DecimalField(..., max_digits=5, decimal_places=2)
 And to store numbers up to approximately one billion with a resolution of 10
 decimal places::
     models.DecimalField(..., max_digits=19, decimal_places=10)
 The admin represents this as an ``<input type="text">`` (a single-line input).
 ``EmailField``
 ~~~~~~~~~~~~~~
 A ``CharField`` that checks that the value is a valid e-mail address.
 This doesn't accept ``max_length``; its ``max_length`` is automatically set to
 .
 ``FileField``
 ~~~~~~~~~~~~~
 A file-upload field. Has one **required** argument:
     ======================  ===================================================
     Argument                Description
     ======================  ===================================================
     ``upload_to``           A local filesystem path that will be appended to
                             your ``MEDIA_ROOT`` setting to determine the
                             output of the ``get_<fieldname>_url()`` helper
                             function.
     ======================  ===================================================
 This path may contain `strftime formatting`_, which will be replaced by the
 date/time of the file upload (so that uploaded files don't fill up the given
 directory).
 The admin represents this field as an ``<input type="file">`` (a file-upload
 widget).
 Using a ``FileField`` or an ``ImageField`` (see below) in a model takes a few
 steps:
 . In your settings file, you'll need to define ``MEDIA_ROOT`` as the
        full path to a directory where you'd like Django to store uploaded
        files. (For performance, these files are not stored in the database.)
        Define ``MEDIA_URL`` as the base public URL of that directory. Make
        sure that this directory is writable by the Web server's user
        account.
 . Add the ``FileField`` or ``ImageField`` to your model, making sure
        to define the ``upload_to`` option to tell Django to which
        subdirectory of ``MEDIA_ROOT`` it should upload files.
 . All that will be stored in your database is a path to the file
        (relative to ``MEDIA_ROOT``). You'll most likely want to use the
        convenience ``get_<fieldname>_url`` function provided by Django. For
        example, if your ``ImageField`` is called ``mug_shot``, you can get
        the absolute URL to your image in a template with ``{{
        object.get_mug_shot_url }}``.
 For example, say your ``MEDIA_ROOT`` is set to ``'/home/media'``, and
 ``upload_to`` is set to ``'photos/%Y/%m/%d'``. The ``'%Y/%m/%d'`` part of
 ``upload_to`` is strftime formatting; ``'%Y'`` is the four-digit year,
 ``'%m'`` is the two-digit month and ``'%d'`` is the two-digit day. If you
 upload a file on Jan. 15, 2007, it will be saved in the directory
 ``/home/media/photos/2007/01/15``.
 If you want to retrieve the upload file's on-disk filename, or a URL that
 refers to that file, or the file's size, you can use the
 ``get_FOO_filename()``, ``get_FOO_url()`` and ``get_FOO_size()`` methods.
 They are all documented here__.
 __ ../db-api/#get-foo-filename
 Note that whenever you deal with uploaded files, you should pay close attention
 to where you're uploading them and what type of files they are, to avoid
 security holes. *Validate all uploaded files* so that you're sure the files are
 what you think they are. For example, if you blindly let somebody upload files,
 without validation, to a directory that's within your Web server's document
 root, then somebody could upload a CGI or PHP script and execute that script by
 visiting its URL on your site. Don't allow that.
 .. _`strftime formatting`: http://docs.python.org/lib/module-time.html#l2h-1941
 ``FilePathField``
 ~~~~~~~~~~~~~~~~~
 A field whose choices are limited to the filenames in a certain directory
 on the filesystem. Has three special arguments, of which the first is
 **required**:
     ======================  ===================================================
     Argument                Description
     ======================  ===================================================
     ``path``                Required. The absolute filesystem path to a
                             directory from which this ``FilePathField`` should
                             get its choices. Example: ``"/home/images"``.
     ``match``               Optional. A regular expression, as a string, that
                             ``FilePathField`` will use to filter filenames.
                             Note that the regex will be applied to the
                             base filename, not the full path. Example:
                             ``"foo.*\.txt$"``, which will match a file called
                             ``foo23.txt`` but not ``bar.txt`` or ``foo23.gif``.
     ``recursive``           Optional. Either ``True`` or ``False``. Default is
                             ``False``. Specifies whether all subdirectories of
                             ``path`` should be included.
     ======================  ===================================================
 Of course, these arguments can be used together.
 The one potential gotcha is that ``match`` applies to the base filename,
 not the full path. So, this example::
     FilePathField(path="/home/images", match="foo.*", recursive=True)
 ...will match ``/home/images/foo.gif`` but not ``/home/images/foo/bar.gif``
 because the ``match`` applies to the base filename (``foo.gif`` and
 ``bar.gif``).
 ``FloatField``
 ~~~~~~~~~~~~~~
 **Changed in Django development version**
 A floating-point number represented in Python by a ``float`` instance.
 The admin represents this as an ``<input type="text">`` (a single-line input).
 **NOTE:** The semantics of ``FloatField`` have changed in the Django
 development version. See the `Django 0.96 documentation`_ for the old behavior.
 .. _Django 0.96 documentation: http://www.djangoproject.com/documentation/0.96/model-api/#floatfield
 ``ImageField``
 ~~~~~~~~~~~~~~
 Like `FileField`_, but validates that the uploaded object is a valid
 image. Has two extra optional arguments, ``height_field`` and
 ``width_field``, which, if set, will be auto-populated with the height and
 width of the image each time a model instance is saved.
 In addition to the special ``get_FOO_*`` methods that are available for
 ``FileField``, an ``ImageField`` also has ``get_FOO_height()`` and
 ``get_FOO_width()`` methods. These are documented elsewhere_.
 Requires the `Python Imaging Library`_.
 .. _Python Imaging Library: http://www.pythonware.com/products/pil/
 .. _elsewhere: ../db-api/#get-foo-height-and-get-foo-width
 ``IntegerField``
 ~~~~~~~~~~~~~~~~
 An integer.
 The admin represents this as an ``<input type="text">`` (a single-line input).
 ``IPAddressField``
 ~~~~~~~~~~~~~~~~~~
 An IP address, in string format (i.e. "24.124.1.30").
 The admin represents this as an ``<input type="text">`` (a single-line input).
 ``NullBooleanField``
 ~~~~~~~~~~~~~~~~~~~~
 Like a ``BooleanField``, but allows ``NULL`` as one of the options.  Use this
 instead of a ``BooleanField`` with ``null=True``.
 The admin represents this as a ``<select>`` box with "Unknown", "Yes" and "No" choices.
 ``PhoneNumberField``
 ~~~~~~~~~~~~~~~~~~~~
 A ``CharField`` that checks that the value is a valid U.S.A.-style phone
 number (in the format ``XXX-XXX-XXXX``).
 ``PositiveIntegerField``
 ~~~~~~~~~~~~~~~~~~~~~~~~
 Like an ``IntegerField``, but must be positive.
 ``PositiveSmallIntegerField``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Like a ``PositiveIntegerField``, but only allows values under a certain
 (database-dependent) point.
 ``SlugField``
 ~~~~~~~~~~~~~
 "Slug" is a newspaper term. A slug is a short label for something,
 containing only letters, numbers, underscores or hyphens. They're generally
 used in URLs.
 Like a CharField, you can specify ``max_length``. If ``max_length`` is
 not specified, Django will use a default length of 50.
 Implies ``db_index=True``.
 Accepts an extra option, ``prepopulate_from``, which is a list of fields
 from which to auto-populate the slug, via JavaScript, in the object's admin
 form::
     models.SlugField(prepopulate_from=("pre_name", "name"))
 ``prepopulate_from`` doesn't accept DateTimeFields, ForeignKeys nor
 ManyToManyFields.
 The admin represents ``SlugField`` as an ``<input type="text">`` (a
 single-line input).
 ``SmallIntegerField``
 ~~~~~~~~~~~~~~~~~~~~~
 Like an ``IntegerField``, but only allows values under a certain
 (database-dependent) point.
 ``TextField``
 ~~~~~~~~~~~~~
 A large text field.
 The admin represents this as a ``<textarea>`` (a multi-line input).
 ``TimeField``
 ~~~~~~~~~~~~~
 A time. Accepts the same auto-population options as ``DateField`` and
 ``DateTimeField``.
 The admin represents this as an ``<input type="text">`` with some
 JavaScript shortcuts.
 ``URLField``
 ~~~~~~~~~~~~
 A field for a URL. If the ``verify_exists`` option is ``True`` (default),
 the URL given will be checked for existence (i.e., the URL actually loads
 and doesn't give a 404 response).
 The admin represents this as an ``<input type="text">`` (a single-line input).
 ``URLField`` takes an optional argument, ``max_length``, the maximum length (in
 characters) of the field. The maximum length is enforced at the database level and
 in Django's validation. If you don't specify ``max_length``, a default of 200
 is used.
 ``USStateField``
 ~~~~~~~~~~~~~~~~
 A two-letter U.S. state abbreviation.
 The admin represents this as an ``<input type="text">`` (a single-line input).
 ``XMLField``
 ~~~~~~~~~~~~
 A ``TextField`` that checks that the value is valid XML that matches a
 given schema. Takes one required argument, ``schema_path``, which is the
 filesystem path to a RelaxNG_ schema against which to validate the field.
 .. _RelaxNG: http://www.relaxng.org/
 Field options
 -------------
 The following arguments are available to all field types. All are optional.
 ``null``
 ~~~~~~~~
 If ``True``, Django will store empty values as ``NULL`` in the database.
 Default is ``False``.
 Note that empty string values will always get stored as empty strings, not
 as ``NULL``. Only use ``null=True`` for non-string fields such as integers,
 booleans and dates. For both types of fields, you will also need to set
 ``blank=True`` if you wish to permit empty values in forms, as the ``null``
 parameter only affects database storage (see blank_, below).
 Avoid using ``null`` on string-based fields such as ``CharField`` and
 ``TextField`` unless you have an excellent reason. If a string-based field
 has ``null=True``, that means it has two possible values for "no data":
 ``NULL``, and the empty string. In most cases, it's redundant to have two
 possible values for "no data;" Django convention is to use the empty
 string, not ``NULL``.
 .. note::
     When using the Oracle database backend, the ``null=True`` option will
     be coerced for string-based fields that can blank, and the value
     ``NULL`` will be stored to denote the empty string.
 ``blank``
 ~~~~~~~~~
 If ``True``, the field is allowed to be blank. Default is ``False``.
 Note that this is different than ``null``. ``null`` is purely
 database-related, whereas ``blank`` is validation-related. If a field has
 ``blank=True``, validation on Django's admin site will allow entry of an
 empty value. If a field has ``blank=False``, the field will be required.
 ``choices``
 ~~~~~~~~~~~
 An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this
 field.
 If this is given, Django's admin will use a select box instead of the
 standard text field and will limit choices to the choices given.
 A choices list looks like this::
     YEAR_IN_SCHOOL_CHOICES = (
         ('FR', 'Freshman'),
         ('SO', 'Sophomore'),
         ('JR', 'Junior'),
         ('SR', 'Senior'),
         ('GR', 'Graduate'),
+    )
 The first element in each tuple is the actual value to be stored. The
 second element is the human-readable name for the option.
 The choices list can be defined either as part of your model class::
     class Foo(models.Model):
         GENDER_CHOICES = (
             ('M', 'Male'),
             ('F', 'Female'),
+        )
         gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
 or outside your model class altogether::
     GENDER_CHOICES = (
         ('M', 'Male'),
         ('F', 'Female'),
+    )
     class Foo(models.Model):
         gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
 For each model field that has ``choices`` set, Django will add a method to
 retrieve the human-readable name for the field's current value. See
 `get_FOO_display`_ in the database API documentation.
 .. _get_FOO_display: ../db-api/#get-foo-display
 Finally, note that choices can be any iterable object -- not necessarily a
 list or tuple. This lets you construct choices dynamically. But if you find
 yourself hacking ``choices`` to be dynamic, you're probably better off using
 a proper database table with a ``ForeignKey``. ``choices`` is meant for static
 data that doesn't change much, if ever.
 ``core``
 ~~~~~~~~
 For objects that are edited inline to a related object.
 In the Django admin, if all "core" fields in an inline-edited object are
 cleared, the object will be deleted.
 It is an error to have an inline-editable relation without at least one
 ``core=True`` field.
 Please note that each field marked "core" is treated as a required field by the
 Django admin site. Essentially, this means you should put ``core=True`` on all
 required fields in your related object that is being edited inline.
 ``db_column``
 ~~~~~~~~~~~~~
 The name of the database column to use for this field. If this isn't given,
 Django will use the field's name.
 If your database column name is an SQL reserved word, or contains
 characters that aren't allowed in Python variable names -- notably, the
 hyphen -- that's OK. Django quotes column and table names behind the
 scenes.
 ``db_index``
 ~~~~~~~~~~~~
 If ``True``, ``django-admin.py sqlindexes`` will output a ``CREATE INDEX``
 statement for this field.
 ``db_tablespace``
 ~~~~~~~~~~~~~~~~~
 **New in Django development version**
 The name of the database tablespace to use for this field's index, if
 indeed this field is indexed. The default is the ``db_tablespace`` of
 the model, if any. If the backend doesn't support tablespaces, this
 option is ignored.
 ``default``
 ~~~~~~~~~~~
 The default value for the field.
 ``editable``
 ~~~~~~~~~~~~
 If ``False``, the field will not be editable in the admin or via form
 processing using the object's ``AddManipulator`` or ``ChangeManipulator``
 classes. Default is ``True``.
 ``help_text``
 ~~~~~~~~~~~~~
 Extra "help" text to be displayed under the field on the object's admin
 form. It's useful for documentation even if your object doesn't have an
 admin form.
 Note that this value is *not* HTML-escaped when it's displayed in the admin
 interface. This lets you include HTML in ``help_text`` if you so desire. For
 example::
         help_text="Please use the following format: <em>YYYY-MM-DD</em>."
 ``primary_key``
 ~~~~~~~~~~~~~~~
 If ``True``, this field is the primary key for the model.
 If you don't specify ``primary_key=True`` for any fields in your model,
 Django will automatically add this field::
     id = models.AutoField('ID', primary_key=True)
 Thus, you don't need to set ``primary_key=True`` on any of your fields
 unless you want to override the default primary-key behavior.
 ``primary_key=True`` implies ``blank=False``, ``null=False`` and
 ``unique=True``. Only one primary key is allowed on an object.
 ``radio_admin``
 ~~~~~~~~~~~~~~~
 By default, Django's admin uses a select-box interface (<select>) for
 fields that are ``ForeignKey`` or have ``choices`` set. If ``radio_admin``
 is set to ``True``, Django will use a radio-button interface instead.
 Don't use this for a field unless it's a ``ForeignKey`` or has ``choices``
 set.
 ``unique``
 ~~~~~~~~~~
 If ``True``, this field must be unique throughout the table.
 This is enforced at the database level and at the Django admin-form level.
 ``unique_for_date``
 ~~~~~~~~~~~~~~~~~~~
 Set this to the name of a ``DateField`` or ``DateTimeField`` to require
 that this field be unique for the value of the date field.
 For example, if you have a field ``title`` that has
 ``unique_for_date="pub_date"``, then Django wouldn't allow the entry of
 two records with the same ``title`` and ``pub_date``.
 This is enforced at the Django admin-form level but not at the database level.
 ``unique_for_month``
 ~~~~~~~~~~~~~~~~~~~~
 Like ``unique_for_date``, but requires the field to be unique with respect
 to the month.
 ``unique_for_year``
 ~~~~~~~~~~~~~~~~~~~
 Like ``unique_for_date`` and ``unique_for_month``.
 ``validator_list``
 ~~~~~~~~~~~~~~~~~~
 A list of extra validators to apply to the field. Each should be a callable
 that takes the parameters ``field_data, all_data`` and raises
 ``django.core.validators.ValidationError`` for errors. (See the
 `validator docs`_.)
 Django comes with quite a few validators. They're in ``django.core.validators``.
 .. _validator docs: ../forms/#validators
 Verbose field names
 -------------------
 Each field type, except for ``ForeignKey``, ``ManyToManyField`` and
 ``OneToOneField``, takes an optional first positional argument -- a
 verbose name. If the verbose name isn't given, Django will automatically create
 it using the field's attribute name, converting underscores to spaces.
 In this example, the verbose name is ``"Person's first name"``::
     first_name = models.CharField("Person's first name", max_length=30)
 In this example, the verbose name is ``"first name"``::
     first_name = models.CharField(max_length=30)
 ``ForeignKey``, ``ManyToManyField`` and ``OneToOneField`` require the first
 argument to be a model class, so use the ``verbose_name`` keyword argument::
     poll = models.ForeignKey(Poll, verbose_name="the related poll")
     sites = models.ManyToManyField(Site, verbose_name="list of sites")
     place = models.OneToOneField(Place, verbose_name="related place")
 Convention is not to capitalize the first letter of the ``verbose_name``.
 Django will automatically capitalize the first letter where it needs to.
 Relationships
 -------------
 Clearly, the power of relational databases lies in relating tables to each
 other. Django offers ways to define the three most common types of database
 relationships: Many-to-one, many-to-many and one-to-one.
 Many-to-one relationships
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 To define a many-to-one relationship, use ``ForeignKey``. You use it just like
 any other ``Field`` type: by including it as a class attribute of your model.
 ``ForeignKey`` requires a positional argument: the class to which the model is
 related.
 For example, if a ``Car`` model has a ``Manufacturer`` -- that is, a
 ``Manufacturer`` makes multiple cars but each ``Car`` only has one
 ``Manufacturer`` -- use the following definitions::
     class Manufacturer(models.Model):
         # ...
     class Car(models.Model):
         manufacturer = models.ForeignKey(Manufacturer)
         # ...
 To create a recursive relationship -- an object that has a many-to-one
 relationship with itself -- use ``models.ForeignKey('self')``.
 If you need to create a relationship on a model that has not yet been defined,
 you can use the name of the model, rather than the model object itself::
     class Car(models.Model):
         manufacturer = models.ForeignKey('Manufacturer')
         # ...
     class Manufacturer(models.Model):
         # ...
 Note, however, that you can only use strings to refer to models in the same
 models.py file -- you cannot use a string to reference a model in a different
 application, or to reference a model that has been imported from elsewhere.
 Behind the scenes, Django appends ``"_id"`` to the field name to create its
 database column name. In the above example, the database table for the ``Car``
 model will have a ``manufacturer_id`` column. (You can change this explicitly
 by specifying ``db_column``; see ``db_column`` below.)  However, your code
 should never have to deal with the database column name, unless you write
 custom SQL. You'll always deal with the field names of your model object.
 It's suggested, but not required, that the name of a ``ForeignKey`` field
 (``manufacturer`` in the example above) be the name of the model, lowercase.
 You can, of course, call the field whatever you want. For example::
     class Car(models.Model):
         company_that_makes_it = models.ForeignKey(Manufacturer)
         # ...
 See the `Many-to-one relationship model example`_ for a full example.
 .. _Many-to-one relationship model example: ../models/many_to_one/
 ``ForeignKey`` fields take a number of extra arguments for defining how the
 relationship should work. All are optional:
     =======================  ============================================================
     Argument                 Description
     =======================  ============================================================
     ``edit_inline``          If not ``False``, this related object is edited
                              "inline" on the related object's page. This means
                              that the object will not have its own admin
                              interface. Use either ``models.TABULAR`` or ``models.STACKED``,
                              which, respectively, designate whether the inline-editable
                              objects are displayed as a table or as a "stack" of
                              fieldsets.
     ``limit_choices_to``     A dictionary of lookup arguments and values (see
                              the `Database API reference`_) that limit the
                              available admin choices for this object. Use this
                              with functions from the Python ``datetime`` module
                              to limit choices of objects by date. For example::
                                 limit_choices_to = {'pub_date__lte': datetime.now}
                              only allows the choice of related objects with a
                              ``pub_date`` before the current date/time to be
                              chosen.
                              Instead of a dictionary this can also be a ``Q`` object
                              (an object with a ``get_sql()`` method) for more complex
                              queries.
                              Not compatible with ``edit_inline``.
     ``max_num_in_admin``     For inline-edited objects, this is the maximum
                              number of related objects to display in the admin.
                              Thus, if a pizza could only have up to 10
                              toppings, ``max_num_in_admin=10`` would ensure
                              that a user never enters more than 10 toppings.
                              Note that this doesn't ensure more than 10 related
                              toppings ever get created. It simply controls the
                              admin interface; it doesn't enforce things at the
                              Python API level or database level.
     ``min_num_in_admin``     The minimum number of related objects displayed in
                              the admin. Normally, at the creation stage,
                              ``num_in_admin`` inline objects are shown, and at
                              the edit stage ``num_extra_on_change`` blank
                              objects are shown in addition to all pre-existing
                              related objects.  However, no fewer than
                              ``min_num_in_admin`` related objects will ever be
                              displayed.
     ``num_extra_on_change``  The number of extra blank related-object fields to
                              show at the change stage.
     ``num_in_admin``         The default number of inline objects to display
                              on the object page at the add stage.
     ``raw_id_admin``         Only display a field for the integer to be entered
                              instead of a drop-down menu. This is useful when
                              related to an object type that will have too many
                              rows to make a select box practical.
                              Not used with ``edit_inline``.
     ``related_name``         The name to use for the relation from the related
                              object back to this one. See the
                              `related objects documentation`_ for a full
                              explanation and example.
     ``to_field``             The field on the related object that the relation
                              is to. By default, Django uses the primary key of
                              the related object.
     =======================  ============================================================
 .. _`Database API reference`: ../db-api/
 .. _related objects documentation: ../db-api/#related-objects
 Many-to-many relationships
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 To define a many-to-many relationship, use ``ManyToManyField``. You use it just
 like any other ``Field`` type: by including it as a class attribute of your
 model.
 ``ManyToManyField`` requires a positional argument: the class to which the
 model is related.
 For example, if a ``Pizza`` has multiple ``Topping`` objects -- that is, a
 ``Topping`` can be on multiple pizzas and each ``Pizza`` has multiple toppings --
 here's how you'd represent that::
     class Topping(models.Model):
         # ...
     class Pizza(models.Model):
         # ...
         toppings = models.ManyToManyField(Topping)
 As with ``ForeignKey``, a relationship to self can be defined by using the
 string ``'self'`` instead of the model name, and you can refer to as-yet
 undefined models by using a string containing the model name. However, you
 can only use strings to refer to models in the same models.py file -- you
 cannot use a string to reference a model in a different application, or to
 reference a model that has been imported from elsewhere.
 It's suggested, but not required, that the name of a ``ManyToManyField``
 (``toppings`` in the example above) be a plural describing the set of related
 model objects.
 Behind the scenes, Django creates an intermediary join table to represent the
 many-to-many relationship.
 It doesn't matter which model gets the ``ManyToManyField``, but you only need
 it in one of the models -- not in both.
 Generally, ``ManyToManyField`` instances should go in the object that's going
 to be edited in the admin interface, if you're using Django's admin. In the
 above example, ``toppings`` is in ``Pizza`` (rather than ``Topping`` having a
 ``pizzas`` ``ManyToManyField`` ) because it's more natural to think about a
 ``Pizza`` having toppings than a topping being on multiple pizzas. The way it's
 set up above, the ``Pizza`` admin form would let users select the toppings.
 See the `Many-to-many relationship model example`_ for a full example.
 .. _Many-to-many relationship model example: ../models/many_to_many/
 ``ManyToManyField`` objects take a number of extra arguments for defining how
 the relationship should work. All are optional:
     =======================  ============================================================
     Argument                 Description
     =======================  ============================================================
     ``related_name``         See the description under ``ForeignKey`` above.
     ``filter_interface``     Use a nifty unobtrusive Javascript "filter" interface
                              instead of the usability-challenged ``<select multiple>``
                              in the admin form for this object. The value should be
                              ``models.HORIZONTAL`` or ``models.VERTICAL`` (i.e.
                              should the interface be stacked horizontally or
                              vertically).
     ``limit_choices_to``     See the description under ``ForeignKey`` above.
     ``symmetrical``          Only used in the definition of ManyToManyFields on self.
                              Consider the following model:
                              class Person(models.Model):
                                  friends = models.ManyToManyField("self")
                              When Django processes this model, it identifies that it has
                              a ``ManyToManyField`` on itself, and as a result, it
                              doesn't add a ``person_set`` attribute to the ``Person``
                              class. Instead, the ``ManyToManyField`` is assumed to be
                              symmetrical -- that is, if I am your friend, then you are
                              my friend.
                              If you do not want symmetry in ``ManyToMany`` relationships
                              with ``self``, set ``symmetrical`` to ``False``. This will
                              force Django to add the descriptor for the reverse
                              relationship, allowing ``ManyToMany`` relationships to be
                              non-symmetrical.
     ``db_table``             The name of the table to create for storing the many-to-many
                              data. If this is not provided, Django will assume a default
                              name based upon the names of the two tables being joined.
     =======================  ============================================================
 One-to-one relationships
 ~~~~~~~~~~~~~~~~~~~~~~~~
 The semantics of one-to-one relationships will be changing soon, so we don't
 recommend you use them. If that doesn't scare you away, keep reading.
 To define a one-to-one relationship, use ``OneToOneField``. You use it just
 like any other ``Field`` type: by including it as a class attribute of your
 model.
 This is most useful on the primary key of an object when that object "extends"
 another object in some way.
 ``OneToOneField`` requires a positional argument: the class to which the
 model is related.
 For example, if you're building a database of "places", you would build pretty
 standard stuff such as address, phone number, etc. in the database. Then, if you
 wanted to build a database of restaurants on top of the places, instead of
 repeating yourself and replicating those fields in the ``Restaurant`` model, you
 could make ``Restaurant`` have a ``OneToOneField`` to ``Place`` (because a
 restaurant "is-a" place).
 As with ``ForeignKey``, a relationship to self can be defined by using the
 string ``"self"`` instead of the model name; references to as-yet undefined
 models can be made by using a string containing the model name.
 This ``OneToOneField`` will actually replace the primary key ``id`` field
 (since one-to-one relations share the same primary key), and will be displayed
 as a read-only field when you edit an object in the admin interface:
 See the `One-to-one relationship model example`_ for a full example.
 .. _One-to-one relationship model example: ../models/one_to_one/
 Custom field types
 ------------------
 **New in Django development version**
 Django's built-in field types don't cover every possible database column type --
 only the common types, such as ``VARCHAR`` and ``INTEGER``. For more obscure
 column types, such as geographic polygons or even user-created types such as
 `PostgreSQL custom types`_, you can define your own Django ``Field`` subclasses.
 .. _PostgreSQL custom types: http://www.postgresql.org/docs/8.2/interactive/sql-createtype.html
 .. admonition:: Experimental territory
     This is an area of Django that traditionally has not been documented, but
     we're starting to include bits of documentation, one feature at a time.
     Please forgive the sparseness of this section.
     If you like living on the edge and are comfortable with the risk of
     unstable, undocumented APIs, see the code for the core ``Field`` class
     in ``django/db/models/fields/__init__.py`` -- but if/when the innards
     change, don't say we didn't warn you.
 To create a custom field type, simply subclass ``django.db.models.Field``.
 Here is an incomplete list of the methods you should implement:
 ``db_type()``
 ~~~~~~~~~~~~~
 Returns the database column data type for the ``Field``, taking into account
 the current ``DATABASE_ENGINE`` setting.
 Say you've created a PostgreSQL custom type called ``mytype``. You can use this
 field with Django by subclassing ``Field`` and implementing the ``db_type()``
 method, like so::
     from django.db import models
     class MytypeField(models.Field):
         def db_type(self):
             return 'mytype'
 Once you have ``MytypeField``, you can use it in any model, just like any other
 ``Field`` type::
     class Person(models.Model):
         name = models.CharField(max_length=80)
         gender = models.CharField(max_length=1)
         something_else = MytypeField()
 If you aim to build a database-agnostic application, you should account for
 differences in database column types. For example, the date/time column type
 in PostgreSQL is called ``timestamp``, while the same column in MySQL is called
 ``datetime``. The simplest way to handle this in a ``db_type()`` method is to
 import the Django settings module and check the ``DATABASE_ENGINE`` setting.
 For example::
     class MyDateField(models.Field):
         def db_type(self):
             from django.conf import settings
             if settings.DATABASE_ENGINE == 'mysql':
                 return 'datetime'
             else:
                 return 'timestamp'
 The ``db_type()`` method is only called by Django when the framework constructs
 the ``CREATE TABLE`` statements for your application -- that is, when you first
 create your tables. It's not called at any other time, so it can afford to
 execute slightly complex code, such as the ``DATABASE_ENGINE`` check in the
 above example.
 Some database column types accept parameters, such as ``CHAR(25)``, where the
 parameter ``25`` represents the maximum column length. In cases like these,
 it's more flexible if the parameter is specified in the model rather than being
 hard-coded in the ``db_type()`` method. For example, it wouldn't make much
 sense to have a ``CharMaxlength25Field``, shown here::
     # This is a silly example of hard-coded parameters.
     class CharMaxlength25Field(models.Field):
         def db_type(self):
             return 'char(25)'
     # In the model:
     class MyModel(models.Model):
         # ...
         my_field = CharMaxlength25Field()
 The better way of doing this would be to make the parameter specifiable at run
 time -- i.e., when the class is instantiated. To do that, just implement
 ``__init__()``, like so::
     # This is a much more flexible example.
     class BetterCharField(models.Field):
         def __init__(self, max_length, *args, **kwargs):
             self.max_length = max_length
             super(BetterCharField, self).__init__(*args, **kwargs)
         def db_type(self):
             return 'char(%s)' % self.max_length
     # In the model:
     class MyModel(models.Model):
         # ...
         my_field = BetterCharField(25)
 Note that if you implement ``__init__()`` on a ``Field`` subclass, it's
 important to call ``Field.__init__()`` -- i.e., the parent class'
 ``__init__()`` method.
 Meta options
 ============
 Give your model metadata by using an inner ``class Meta``, like so::
     class Foo(models.Model):
         bar = models.CharField(max_length=30)
         class Meta:
             # ...
 Model metadata is "anything that's not a field", such as ordering options, etc.
 Here's a list of all possible ``Meta`` options. No options are required. Adding
 ``class Meta`` to a model is completely optional.
 ``db_table``
 ------------
 The name of the database table to use for the model::
     db_table = 'music_album'
 If this isn't given, Django will use ``app_label + '_' + model_class_name``.
 See "Table names" below for more.
 If your database table name is an SQL reserved word, or contains characters
 that aren't allowed in Python variable names -- notably, the hyphen --
 that's OK. Django quotes column and table names behind the scenes.
 ``db_tablespace``
 -----------------
 **New in Django development version**
 The name of the database tablespace to use for the model. If the backend
 doesn't support tablespaces, this option is ignored.
 ``get_latest_by``
 -----------------
 The name of a ``DateField`` or ``DateTimeField`` in the model. This specifies
 the default field to use in your model ``Manager``'s ``latest()`` method.
 Example::
     get_latest_by = "order_date"
 See the `docs for latest()`_ for more.
 .. _docs for latest(): ../db-api/#latest-field-name-none
 ``order_with_respect_to``
 -------------------------
 Marks this object as "orderable" with respect to the given field. This is
 almost always used with related objects to allow them to be ordered with
 respect to a parent object. For example, if an ``Answer`` relates to a
 ``Question`` object, and a question has more than one answer, and the order
 of answers matters, you'd do this::
     class Answer(models.Model):
         question = models.ForeignKey(Question)
         # ...
         class Meta:
             order_with_respect_to = 'question'
 ``ordering``
 ------------
 The default ordering for the object, for use when obtaining lists of objects::
     ordering = ['-order_date']
 This is a tuple or list of strings. Each string is a field name with an
 optional "-" prefix, which indicates descending order. Fields without a
 leading "-" will be ordered ascending. Use the string "?" to order randomly.
 For example, to order by a ``pub_date`` field ascending, use this::
     ordering = ['pub_date']
 To order by ``pub_date`` descending, use this::
     ordering = ['-pub_date']
 To order by ``pub_date`` descending, then by ``author`` ascending, use this::
     ordering = ['-pub_date', 'author']
 See `Specifying ordering`_ for more examples.
 Note that, regardless of how many fields are in ``ordering``, the admin
 site uses only the first field.
 .. _Specifying ordering: ../models/ordering/
 ``permissions``
 ---------------
 Extra permissions to enter into the permissions table when creating this
 object. Add, delete and change permissions are automatically created for
 each object that has ``admin`` set. This example specifies an extra
 permission, ``can_deliver_pizzas``::
     permissions = (("can_deliver_pizzas", "Can deliver pizzas"),)
 This is a list or tuple of 2-tuples in the format
 ``(permission_code, human_readable_permission_name)``.
 ``unique_together``
 -------------------
 Sets of field names that, taken together, must be unique::
     unique_together = (("driver", "restaurant"),)
 This is a list of lists of fields that must be unique when considered
 together. It's used in the Django admin and is enforced at the database
 level (i.e., the appropriate ``UNIQUE`` statements are included in the
 ``CREATE TABLE`` statement).
 ``verbose_name``
 ----------------
 A human-readable name for the object, singular::
     verbose_name = "pizza"
 If this isn't given, Django will use a munged version of the class name:
 ``CamelCase`` becomes ``camel case``.
 ``verbose_name_plural``
 -----------------------
 The plural name for the object::
     verbose_name_plural = "stories"
 If this isn't given, Django will use ``verbose_name + "s"``.
 Table names
 ===========
 To save you time, Django automatically derives the name of the database table
 from the name of your model class and the app that contains it. A model's
 database table name is constructed by joining the model's "app label" -- the
 name you used in ``manage.py startapp`` -- to the model's class name, with an
 underscore between them.
 For example, if you have an app ``bookstore`` (as created by
 ``manage.py startapp bookstore``), a model defined as ``class Book`` will have
 a database table named ``bookstore_book``.
 To override the database table name, use the ``db_table`` parameter in
 ``class Meta``.
 Automatic primary key fields
 ============================
 By default, Django gives each model the following field::
     id = models.AutoField(primary_key=True)
 This is an auto-incrementing primary key.
 If you'd like to specify a custom primary key, just specify ``primary_key=True``
 on one of your fields. If Django sees you've explicitly set ``primary_key``, it
 won't add the automatic ``id`` column.
 Each model requires exactly one field to have ``primary_key=True``.
 Admin options
 =============
 If you want your model to be visible to Django's admin site, give your model an
 inner ``"class Admin"``, like so::
     class Person(models.Model):
         first_name = models.CharField(max_length=30)
         last_name = models.CharField(max_length=30)
         class Admin:
             # Admin options go here
             pass
 The ``Admin`` class tells Django how to display the model in the admin site.
 Here's a list of all possible ``Admin`` options. None of these options are
 required. To use an admin interface without specifying any options, use
 ``pass``, like so::
     class Admin:
         pass
 Adding ``class Admin`` to a model is completely optional.
 ``date_hierarchy``
 ------------------
 Set ``date_hierarchy`` to the name of a ``DateField`` or ``DateTimeField`` in
 your model, and the change list page will include a date-based drilldown
 navigation by that field.
 Example::
     date_hierarchy = 'pub_date'
 ``fields``
 ----------
 Set ``fields`` to control the layout of admin "add" and "change" pages.
 ``fields`` is a list of two-tuples, in which each two-tuple represents a
 ``<fieldset>`` on the admin form page. (A ``<fieldset>`` is a "section" of the
 form.)
 The two-tuples are in the format ``(name, field_options)``, where ``name`` is a
 string representing the title of the fieldset and ``field_options`` is a
 dictionary of information about the fieldset, including a list of fields to be
 displayed in it.
 A full example, taken from the ``django.contrib.flatpages.FlatPage`` model::
     class Admin:
         fields = (
             (None, {
                 'fields': ('url', 'title', 'content', 'sites')
             }),
             ('Advanced options', {
                 'classes': 'collapse',
                 'fields' : ('enable_comments', 'registration_required', 'template_name')
             }),
+        )
 This results in an admin page that looks like:
     .. image:: http://media.djangoproject.com/img/doc/flatfiles_admin.png
 If ``fields`` isn't given, Django will default to displaying each field that
 isn't an ``AutoField`` and has ``editable=True``, in a single fieldset, in
 the same order as the fields are defined in the model.
 The ``field_options`` dictionary can have the following keys:
 ``fields``
 ~~~~~~~~~~
 A tuple of field names to display in this fieldset. This key is required.
 Example::
+    {
     'fields': ('first_name', 'last_name', 'address', 'city', 'state'),
+    }
 To display multiple fields on the same line, wrap those fields in their own
 tuple. In this example, the ``first_name`` and ``last_name`` fields will
 display on the same line::
+    {
     'fields': (('first_name', 'last_name'), 'address', 'city', 'state'),
+    }
 ``classes``
 ~~~~~~~~~~~
 A string containing extra CSS classes to apply to the fieldset.
 Example::
+    {
     'classes': 'wide',
+    }
 Apply multiple classes by separating them with spaces. Example::
+    {
     'classes': 'wide extrapretty',
+    }
 Two useful classes defined by the default admin-site stylesheet are
 ``collapse`` and ``wide``. Fieldsets with the ``collapse`` style will be
 initially collapsed in the admin and replaced with a small "click to expand"
 link. Fieldsets with the ``wide`` style will be given extra horizontal space.
 ``description``
 ~~~~~~~~~~~~~~~
 A string of optional extra text to be displayed at the top of each fieldset,
 under the heading of the fieldset. It's used verbatim, so you can use any HTML
 and you must escape any special HTML characters (such as ampersands) yourself.
 ``js``
 ------
 A list of strings representing URLs of JavaScript files to link into the admin
 screen via ``<script src="">`` tags. This can be used to tweak a given type of
 admin page in JavaScript or to provide "quick links" to fill in default values
 for certain fields.
 If you use relative URLs -- URLs that don't start with ``http://`` or ``/`` --
 then the admin site will automatically prefix these links with
 ``settings.ADMIN_MEDIA_PREFIX``.
 ``list_display``
 ----------------
 Set ``list_display`` to control which fields are displayed on the change list
 page of the admin.
 Example::
     list_display = ('first_name', 'last_name')
 If you don't set ``list_display``, the admin site will display a single column
 that displays the ``__str__()`` representation of each object.
 A few special cases to note about ``list_display``:
     * If the field is a ``ForeignKey``, Django will display the
       ``__unicode__()`` of the related object.
     * ``ManyToManyField`` fields aren't supported, because that would entail
       executing a separate SQL statement for each row in the table. If you
       want to do this nonetheless, give your model a custom method, and add
       that method's name to ``list_display``. (See below for more on custom
       methods in ``list_display``.)
     * If the field is a ``BooleanField`` or ``NullBooleanField``, Django will
       display a pretty "on" or "off" icon instead of ``True`` or ``False``.
     * If the string given is a method of the model, Django will call it and
       display the output. This method should have a ``short_description``
       function attribute, for use as the header for the field.
       Here's a full example model::
           class Person(models.Model):
               name = models.CharField(max_length=50)
               birthday = models.DateField()
               class Admin:
                   list_display = ('name', 'decade_born_in')
               def decade_born_in(self):
                   return self.birthday.strftime('%Y')[:3] + "0's"
               decade_born_in.short_description = 'Birth decade'
     * If the string given is a method of the model, Django will HTML-escape the
       output by default. If you'd rather not escape the output of the method,
       give the method an ``allow_tags`` attribute whose value is ``True``.
       Here's a full example model::
           class Person(models.Model):
               first_name = models.CharField(max_length=50)
               last_name = models.CharField(max_length=50)
               color_code = models.CharField(max_length=6)
               class Admin:
                   list_display = ('first_name', 'last_name', 'colored_name')
               def colored_name(self):
                   return '<span style="color: #%s;">%s %s</span>' % (self.color_code, self.first_name, self.last_name)
               colored_name.allow_tags = True
     * If the string given is a method of the model that returns True or False
       Django will display a pretty "on" or "off" icon if you give the method a
       ``boolean`` attribute whose value is ``True``.
       Here's a full example model::
           class Person(models.Model):
               first_name = models.CharField(max_length=50)
               birthday = models.DateField()
               class Admin:
                   list_display = ('name', 'born_in_fifties')
               def born_in_fifties(self):
                   return self.birthday.strftime('%Y')[:3] == 5
               born_in_fifties.boolean = True
     * The ``__str__()`` and ``__unicode__()`` methods are just as valid in
       ``list_display`` as any other model method, so it's perfectly OK to do
       this::
           list_display = ('__unicode__', 'some_other_field')
     * Usually, elements of ``list_display`` that aren't actual database fields
       can't be used in sorting (because Django does all the sorting at the
       database level).
       However, if an element of ``list_display`` represents a certain database
       field, you can indicate this fact by setting the ``admin_order_field``
       attribute of the item.
       For example::
         class Person(models.Model):
             first_name = models.CharField(max_length=50)
             color_code = models.CharField(max_length=6)
             class Admin:
                 list_display = ('first_name', 'colored_first_name')
             def colored_first_name(self):
                 return '<span style="color: #%s;">%s</span>' % (self.color_code, self.first_name)
             colored_first_name.allow_tags = True
             colored_first_name.admin_order_field = 'first_name'
       The above will tell Django to order by the ``first_name`` field when
       trying to sort by ``colored_first_name`` in the admin.
 ``list_display_links``
 ----------------------
 Set ``list_display_links`` to control which fields in ``list_display`` should
 be linked to the "change" page for an object.
 By default, the change list page will link the first column -- the first field
 specified in ``list_display`` -- to the change page for each item. But
 ``list_display_links`` lets you change which columns are linked. Set
 ``list_display_links`` to a list or tuple of field names (in the same format as
 ``list_display``) to link.
 ``list_display_links`` can specify one or many field names. As long as the
 field names appear in ``list_display``, Django doesn't care how many (or how
 few) fields are linked. The only requirement is: If you want to use
 ``list_display_links``, you must define ``list_display``.
 In this example, the ``first_name`` and ``last_name`` fields will be linked on
 the change list page::
     class Admin:
         list_display = ('first_name', 'last_name', 'birthday')
         list_display_links = ('first_name', 'last_name')
 Finally, note that in order to use ``list_display_links``, you must define
 ``list_display``, too.
 ``list_filter``
 ---------------
 Set ``list_filter`` to activate filters in the right sidebar of the change list
 page of the admin. This should be a list of field names, and each specified
 field should be either a ``BooleanField``, ``DateField``, ``DateTimeField``
 or ``ForeignKey``.
 This example, taken from the ``django.contrib.auth.models.User`` model, shows
 how both ``list_display`` and ``list_filter`` work::
     class Admin:
         list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff')
         list_filter = ('is_staff', 'is_superuser')
 The above code results in an admin change list page that looks like this:
     .. image:: http://media.djangoproject.com/img/doc/users_changelist.png
 (This example also has ``search_fields`` defined. See below.)
 ``list_per_page``
 -----------------
 Set ``list_per_page`` to control how many items appear on each paginated admin
 change list page. By default, this is set to ``100``.
 ``list_select_related``
 -----------------------
 Set ``list_select_related`` to tell Django to use ``select_related()`` in
 retrieving the list of objects on the admin change list page. This can save you
 a bunch of database queries.
 The value should be either ``True`` or ``False``. Default is ``False``.
 Note that Django will use ``select_related()``, regardless of this setting,
 if one of the ``list_display`` fields is a ``ForeignKey``.
 For more on ``select_related()``, see `the select_related() docs`_.
 .. _the select_related() docs: ../db-api/#select-related
 ``ordering``
 ------------
 Set ``ordering`` to specify how objects on the admin change list page should be
 ordered. This should be a list or tuple in the same format as a model's
 ``ordering`` parameter.
 If this isn't provided, the Django admin will use the model's default ordering.
 ``save_as``
 -----------
 Set ``save_as`` to enable a "save as" feature on admin change forms.
 Normally, objects have three save options: "Save", "Save and continue editing"
 and "Save and add another". If ``save_as`` is ``True``, "Save and add another"
 will be replaced by a "Save as" button.
 "Save as" means the object will be saved as a new object (with a new ID),
 rather than the old object.
 By default, ``save_as`` is set to ``False``.
 ``save_on_top``
 ---------------
 Set ``save_on_top`` to add save buttons across the top of your admin change
 forms.
 Normally, the save buttons appear only at the bottom of the forms. If you set
 ``save_on_top``, the buttons will appear both on the top and the bottom.
 By default, ``save_on_top`` is set to ``False``.
 ``search_fields``
 -----------------
 Set ``search_fields`` to enable a search box on the admin change list page.
 This should be set to a list of field names that will be searched whenever
 somebody submits a search query in that text box.
 These fields should be some kind of text field, such as ``CharField`` or
 ``TextField``. You can also perform a related lookup on a ``ForeignKey`` with
 the lookup API "follow" notation::
     search_fields = ['foreign_key__related_fieldname']
 When somebody does a search in the admin search box, Django splits the search
 query into words and returns all objects that contain each of the words, case
 insensitive, where each word must be in at least one of ``search_fields``. For
 example, if ``search_fields`` is set to ``['first_name', 'last_name']`` and a
 user searches for ``john lennon``, Django will do the equivalent of this SQL
 ``WHERE`` clause::
     WHERE (first_name ILIKE '%john%' OR last_name ILIKE '%john%')
     AND (first_name ILIKE '%lennon%' OR last_name ILIKE '%lennon%')
 For faster and/or more restrictive searches, prefix the field name
 with an operator:
 ``^``
     Matches the beginning of the field. For example, if ``search_fields`` is
     set to ``['^first_name', '^last_name']`` and a user searches for
     ``john lennon``, Django will do the equivalent of this SQL ``WHERE``
     clause::
         WHERE (first_name ILIKE 'john%' OR last_name ILIKE 'john%')
         AND (first_name ILIKE 'lennon%' OR last_name ILIKE 'lennon%')
     This query is more efficient than the normal ``'%john%'`` query, because
     the database only needs to check the beginning of a column's data, rather
     than seeking through the entire column's data. Plus, if the column has an
     index on it, some databases may be able to use the index for this query,
     even though it's a ``LIKE`` query.
 ``=``
     Matches exactly, case-insensitive. For example, if
     ``search_fields`` is set to ``['=first_name', '=last_name']`` and
     a user searches for ``john lennon``, Django will do the equivalent
     of this SQL ``WHERE`` clause::
         WHERE (first_name ILIKE 'john' OR last_name ILIKE 'john')
         AND (first_name ILIKE 'lennon' OR last_name ILIKE 'lennon')
     Note that the query input is split by spaces, so, following this example,
     it's currently not possible to search for all records in which
     ``first_name`` is exactly ``'john winston'`` (containing a space).
 ``@``
     Performs a full-text match. This is like the default search method but uses
     an index. Currently this is only available for MySQL.
 Managers
 ========
 A ``Manager`` is the interface through which database query operations are
 provided to Django models. At least one ``Manager`` exists for every model in
 a Django application.
 The way ``Manager`` classes work is documented in the `Retrieving objects`_
 section of the database API docs, but this section specifically touches on
 model options that customize ``Manager`` behavior.
 .. _Retrieving objects: ../db-api/#retrieving-objects
 Manager names
 -------------
 By default, Django adds a ``Manager`` with the name ``objects`` to every Django
 model class. However, if you want to use ``objects`` as a field name, or if you
 want to use a name other than ``objects`` for the ``Manager``, you can rename
 it on a per-model basis. To rename the ``Manager`` for a given class, define a
 class attribute of type ``models.Manager()`` on that model. For example::
     from django.db import models
     class Person(models.Model):
         #...
         people = models.Manager()
 Using this example model, ``Person.objects`` will generate an
 ``AttributeError`` exception, but ``Person.people.all()`` will provide a list
 of all ``Person`` objects.
 Custom Managers
 ---------------
 You can use a custom ``Manager`` in a particular model by extending the base
 ``Manager`` class and instantiating your custom ``Manager`` in your model.
 There are two reasons you might want to customize a ``Manager``: to add extra
 ``Manager`` methods, and/or to modify the initial ``QuerySet`` the ``Manager``
 returns.
 Adding extra Manager methods
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Adding extra ``Manager`` methods is the preferred way to add "table-level"
 functionality to your models. (For "row-level" functionality -- i.e., functions
 that act on a single instance of a model object -- use _`Model methods`, not
 custom ``Manager`` methods.)
 A custom ``Manager`` method can return anything you want. It doesn't have to
 return a ``QuerySet``.
 For example, this custom ``Manager`` offers a method ``with_counts()``, which
 returns a list of all ``OpinionPoll`` objects, each with an extra
 ``num_responses`` attribute that is the result of an aggregate query::
     class PollManager(models.Manager):
         def with_counts(self):
             from django.db import connection
             cursor = connection.cursor()
             cursor.execute("""
                 SELECT p.id, p.question, p.poll_date, COUNT(*)
                 FROM polls_opinionpoll p, polls_response r
                 WHERE p.id = r.poll_id
                 GROUP BY 1, 2, 3
                 ORDER BY 3 DESC""")
             result_list = []
             for row in cursor.fetchall():
                 p = self.model(id=row[0], question=row[1], poll_date=row[2])
                 p.num_responses = row[3]
                 result_list.append(p)
             return result_list
     class OpinionPoll(models.Model):
         question = models.CharField(max_length=200)
         poll_date = models.DateField()
         objects = PollManager()
     class Response(models.Model):
         poll = models.ForeignKey(Poll)
         person_name = models.CharField(max_length=50)
         response = models.TextField()
 With this example, you'd use ``OpinionPoll.objects.with_counts()`` to return
 that list of ``OpinionPoll`` objects with ``num_responses`` attributes.
 Another thing to note about this example is that ``Manager`` methods can
 access ``self.model`` to get the model class to which they're attached.
 Modifying initial Manager QuerySets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 A ``Manager``'s base ``QuerySet`` returns all objects in the system. For
 example, using this model::
     class Book(models.Model):
         title = models.CharField(max_length=100)
         author = models.CharField(max_length=50)
 ...the statement ``Book.objects.all()`` will return all books in the database.
 You can override a ``Manager``\'s base ``QuerySet`` by overriding the
 ``Manager.get_query_set()`` method. ``get_query_set()`` should return a
 ``QuerySet`` with the properties you require.
 For example, the following model has *two* ``Manager``\s -- one that returns
 all objects, and one that returns only the books by Roald Dahl::
     # First, define the Manager subclass.
     class DahlBookManager(models.Manager):
         def get_query_set(self):
             return super(DahlBookManager, self).get_query_set().filter(author='Roald Dahl')
     # Then hook it into the Book model explicitly.
     class Book(models.Model):
         title = models.CharField(max_length=100)
         author = models.CharField(max_length=50)
         objects = models.Manager() # The default manager.
         dahl_objects = DahlBookManager() # The Dahl-specific manager.
 With this sample model, ``Book.objects.all()`` will return all books in the
 database, but ``Book.dahl_objects.all()`` will only return the ones written by
 Roald Dahl.
 Of course, because ``get_query_set()`` returns a ``QuerySet`` object, you can
 use ``filter()``, ``exclude()`` and all the other ``QuerySet`` methods on it.
 So these statements are all legal::
     Book.dahl_objects.all()
     Book.dahl_objects.filter(title='Matilda')
     Book.dahl_objects.count()
 This example also pointed out another interesting technique: using multiple
 managers on the same model. You can attach as many ``Manager()`` instances to
 a model as you'd like. This is an easy way to define common "filters" for your
 models.
 For example::
     class MaleManager(models.Manager):
         def get_query_set(self):
             return super(MaleManager, self).get_query_set().filter(sex='M')
     class FemaleManager(models.Manager):
         def get_query_set(self):
             return super(FemaleManager, self).get_query_set().filter(sex='F')
     class Person(models.Model):
         first_name = models.CharField(max_length=50)
         last_name = models.CharField(max_length=50)
         sex = models.CharField(max_length=1, choices=(('M', 'Male'), ('F', 'Female')))
         people = models.Manager()
         men = MaleManager()
         women = FemaleManager()
 This example allows you to request ``Person.men.all()``, ``Person.women.all()``,
 and ``Person.people.all()``, yielding predictable results.
 If you use custom ``Manager`` objects, take note that the first ``Manager``
 Django encounters (in order by which they're defined in the model) has a
 special status. Django interprets the first ``Manager`` defined in a class as
 the "default" ``Manager``. Certain operations -- such as Django's admin site --
 use the default ``Manager`` to obtain lists of objects, so it's generally a
 good idea for the first ``Manager`` to be relatively unfiltered. In the last
 example, the ``people`` ``Manager`` is defined first -- so it's the default
 ``Manager``.
 Model methods
 =============
 Define custom methods on a model to add custom "row-level" functionality to
 your objects. Whereas ``Manager`` methods are intended to do "table-wide"
 things, model methods should act on a particular model instance.
 This is a valuable technique for keeping business logic in one place -- the
 model.
 For example, this model has a few custom methods::
     class Person(models.Model):
         first_name = models.CharField(max_length=50)
         last_name = models.CharField(max_length=50)
         birth_date = models.DateField()
         address = models.CharField(max_length=100)
         city = models.CharField(max_length=50)
         state = models.USStateField() # Yes, this is America-centric...
         def baby_boomer_status(self):
             "Returns the person's baby-boomer status."
             import datetime
             if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
                 return "Baby boomer"
             if self.birth_date < datetime.date(1945, 8, 1):
                 return "Pre-boomer"
             return "Post-boomer"
         def is_midwestern(self):
             "Returns True if this person is from the Midwest."
             return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')
         def _get_full_name(self):
             "Returns the person's full name."
             return '%s %s' % (self.first_name, self.last_name)
         full_name = property(_get_full_name)
 The last method in this example is a *property*. `Read more about properties`_.
 .. _Read more about properties: http://www.python.org/download/releases/2.2/descrintro/#property
 A few object methods have special meaning:
 ``__str__``
 -----------
 ``__str__()`` is a Python "magic method" that defines what should be returned
 if you call ``str()`` on the object. Django uses ``str(obj)`` (or the related
 function, ``unicode(obj)`` -- see below) in a number of places, most notably
 as the value displayed to render an object in the Django admin site and as the
 value inserted into a template when it displays an object. Thus, you should
 always return a nice, human-readable string for the object's ``__str__``.
 Although this isn't required, it's strongly encouraged (see the description of
 ``__unicode__``, below, before putting ``__str__`` methods everywhere).
 For example::
     class Person(models.Model):
         first_name = models.CharField(max_length=50)
         last_name = models.CharField(max_length=50)
         def __str__(self):
             # Note use of django.utils.encoding.smart_str() here because
             # first_name and last_name will be unicode strings.
             return smart_str('%s %s' % (self.first_name, self.last_name))
 ``__unicode__``
 ---------------
 The ``__unicode__()`` method is called whenever you call ``unicode()`` on an
 object. Since Django's database backends will return Unicode strings in your
 model's attributes, you would normally want to write a ``__unicode__()``
 method for your model. The example in the previous section could be written
 more simply as::
     class Person(models.Model):
         first_name = models.CharField(max_length=50)
         last_name = models.CharField(max_length=50)
         def __unicode__(self):
             return u'%s %s' % (self.first_name, self.last_name)
 If you define a ``__unicode__()`` method on your model and not a ``__str__()``
 method, Django will automatically provide you with a ``__str__()`` that calls
 ``__unicode()__`` and then converts the result correctly to a UTF-8 encoded
 string object. This is recommended development practice: define only
 ``__unicode__()`` and let Django take care of the conversion to string objects
 when required.
 ``get_absolute_url``
 --------------------
 Define a ``get_absolute_url()`` method to tell Django how to calculate the
 URL for an object. For example::
     def get_absolute_url(self):
         return "/people/%i/" % self.id
 Django uses this in its admin interface. If an object defines
 ``get_absolute_url()``, the object-editing page will have a "View on site"
 link that will jump you directly to the object's public view, according to
 ``get_absolute_url()``.
 Also, a couple of other bits of Django, such as the `syndication feed framework`_,
 use ``get_absolute_url()`` as a convenience to reward people who've defined the
 method.
 .. _syndication feed framework: ../syndication_feeds/
 It's good practice to use ``get_absolute_url()`` in templates, instead of
 hard-coding your objects' URLs. For example, this template code is bad::
     <a href="/people/{{ object.id }}/">{{ object.name }}</a>
 But this template code is good::
     <a href="{{ object.get_absolute_url }}">{{ object.name }}</a>
 .. note::
     The string you return from ``get_absolute_url()`` must contain only ASCII
     characters (required by the URI spec, `RFC 2396`_) that have been
     URL-encoded, if necessary. Code and templates using ``get_absolute_url()``
     should be able to use the result directly without needing to do any
     further processing. You may wish to use the
     ``django.utils.encoding.iri_to_uri()`` function to help with this if you
     are using unicode strings a lot.
 .. _RFC 2396: http://www.ietf.org/rfc/rfc2396.txt
 The ``permalink`` decorator
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The problem with the way we wrote ``get_absolute_url()`` above is that it
 slightly violates the DRY principle: the URL for this object is defined both
 in the URLConf file and in the model.
 You can further decouple your models from the URLconf using the ``permalink``
 decorator. This decorator is passed the view function, a list of positional
 parameters and (optionally) a dictionary of named parameters. Django then
 works out the correct full URL path using the URLconf, substituting the
 parameters you have given into the URL. For example, if your URLconf
 contained a line such as::
     (r'^people/(\d+)/$', 'people.views.details'),
 ...your model could have a ``get_absolute_url`` method that looked like this::
     from django.db.models import permalink
     def get_absolute_url(self):
         return ('people.views.details', [str(self.id)])
     get_absolute_url = permalink(get_absolute_url)
 Similarly, if you had a URLconf entry that looked like::
     (r'/archive/(?P<year>\d{4})/(?P<month>\d{1,2})/(?P<day>\d{1,2})/$', archive_view)
 ...you could reference this using ``permalink()`` as follows::
     def get_absolute_url(self):
         return ('archive_view', (), {
             'year': self.created.year,
             'month': self.created.month,
             'day': self.created.day})
     get_absolute_url = permalink(get_absolute_url)
 Notice that we specify an empty sequence for the second parameter in this case,
 because we only want to pass keyword parameters, not positional ones.
 In this way, you're tying the model's absolute URL to the view that is used
 to display it, without repeating the URL information anywhere. You can still
 use the ``get_absolute_url`` method in templates, as before.
 Executing custom SQL
 --------------------
 Feel free to write custom SQL statements in custom model methods and
 module-level methods. The object ``django.db.connection`` represents the
 current database connection. To use it, call ``connection.cursor()`` to get a
 cursor object. Then, call ``cursor.execute(sql, [params])`` to execute the SQL
 and ``cursor.fetchone()`` or ``cursor.fetchall()`` to return the resulting
 rows. Example::
     def my_custom_sql(self):
         from django.db import connection
         cursor = connection.cursor()
         cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
         row = cursor.fetchone()
         return row
 ``connection`` and ``cursor`` mostly implement the standard `Python DB-API`_
 (except when it comes to `transaction handling`_). If you're not familiar with
 the Python DB-API, note that the SQL statement in ``cursor.execute()`` uses
 placeholders, ``"%s"``, rather than adding parameters directly within the SQL.
 If you use this technique, the underlying database library will automatically
 add quotes and escaping to your parameter(s) as necessary. (Also note that
 Django expects the ``"%s"`` placeholder, *not* the ``"?"`` placeholder, which is
 used by the SQLite Python bindings. This is for the sake of consistency and
 sanity.)
 A final note: If all you want to do is a custom ``WHERE`` clause, you can just
 use the ``where``, ``tables`` and ``params`` arguments to the standard lookup
 API. See `Other lookup options`_.
 .. _Python DB-API: http://www.python.org/peps/pep-0249.html
 .. _Other lookup options: ../db-api/#extra-select-none-where-none-params-none-tables-none
 .. _transaction handling: ../transactions/
 Overriding default model methods
 --------------------------------
 As explained in the `database API docs`_, each model gets a few methods
 automatically -- most notably, ``save()`` and ``delete()``. You can override
 these methods to alter behavior.
 A classic use-case for overriding the built-in methods is if you want something
 to happen whenever you save an object. For example::
     class Blog(models.Model):
         name = models.CharField(max_length=100)
         tagline = models.TextField()
         def save(self):
             do_something()
             super(Blog, self).save() # Call the "real" save() method.
             do_something_else()
 You can also prevent saving::
     class Blog(models.Model):
         name = models.CharField(max_length=100)
         tagline = models.TextField()
         def save(self):
             if self.name == "Yoko Ono's blog":
                 return # Yoko shall never have her own blog!
             else:
                 super(Blog, self).save() # Call the "real" save() method.
 .. _database API docs: ../db-api/
 Models across files
 ===================
 It's perfectly OK to relate a model to one from another app. To do this, just
 import the related model at the top of the model that holds your model. Then,
 just refer to the other model class wherever needed. For example::
     from mysite.geography.models import ZipCode
     class Restaurant(models.Model):
         # ...
         zip_code = models.ForeignKey(ZipCode)
 Using models
 ============
 Once you have created your models, the final step is to tell Django you're
 going to *use* those models.
 Do this by editing your settings file and changing the ``INSTALLED_APPS``
 setting to add the name of the module that contains your ``models.py``.
 For example, if the models for your application live in the module
 ``mysite.myapp.models`` (the package structure that is created for an
 application by the ``manage.py startapp`` script), ``INSTALLED_APPS`` should
 read, in part::
     INSTALLED_APPS = (
         #...
         'mysite.myapp',
         #...
+    )
 Providing initial SQL data
 ==========================
 Django provides a hook for passing the database arbitrary SQL that's executed
 just after the CREATE TABLE statements. Use this hook, for example, if you want
 to populate default records, or create SQL functions, automatically.
 The hook is simple: Django just looks for a file called
 ``<appname>/sql/<modelname>.sql``, where ``<appname>`` is your app directory and
 ``<modelname>`` is the model's name in lowercase.
 In the ``Person`` example model at the top of this document, assuming it lives
 in an app called ``myapp``, you could add arbitrary SQL to the file
 ``myapp/sql/person.sql``. Here's an example of what the file might contain::
     INSERT INTO myapp_person (first_name, last_name) VALUES ('John', 'Lennon');
     INSERT INTO myapp_person (first_name, last_name) VALUES ('Paul', 'McCartney');
 Each SQL file, if given, is expected to contain valid SQL. The SQL files are
 piped directly into the database after all of the models' table-creation
 statements have been executed.
 The SQL files are read by the ``sqlcustom``, ``sqlreset``, ``sqlall`` and
 ``reset`` commands in ``manage.py``. Refer to the `manage.py documentation`_
 for more information.
 Note that if you have multiple SQL data files, there's no guarantee of the
 order in which they're executed. The only thing you can assume is that, by the
 time your custom data files are executed, all the database tables already will
 have been created.
 .. _`manage.py documentation`: ../django-admin/#sqlcustom-appname-appname
 Database-backend-specific SQL data
 ----------------------------------
 There's also a hook for backend-specific SQL data. For example, you can have
 separate initial-data files for PostgreSQL and MySQL. For each app, Django
 looks for a file called ``<appname>/sql/<modelname>.<backend>.sql``, where
 ``<appname>`` is your app directory, ``<modelname>`` is the model's name in
 lowercase and ``<backend>`` is the value of ``DATABASE_ENGINE`` in your
 settings file (e.g., ``postgresql``, ``mysql``).
 Backend-specific SQL data is executed before non-backend-specific SQL data. For
 example, if your app contains the files ``sql/person.sql`` and
 ``sql/person.postgresql.sql`` and you're installing the app on PostgreSQL,
 Django will execute the contents of ``sql/person.postgresql.sql`` first, then
 ``sql/person.sql``.
+===============
+Model reference
+===============
+A model is the single, definitive source of data about your data. It contains
+the essential fields and behaviors of the data you're storing. Generally, each
+model maps to a single database table.
+The basics:
+    * Each model is a Python class that subclasses ``django.db.models.Model``.
+    * Each attribute of the model represents a database field.
+    * Model metadata (non-field information) goes in an inner class named
+      ``Meta``.
+    * Metadata used for Django's admin site goes into an inner class named
+      ``Admin``.
+    * With all of this, Django gives you an automatically-generated
+      database-access API, which is explained in the `Database API reference`_.
+A companion to this document is the `official repository of model examples`_.
+(In the Django source distribution, these examples are in the
+``tests/modeltests`` directory.)
+.. _Database API reference: ../db-api/
+.. _official repository of model examples: ../models/
+Quick example
+=============
+This example model defines a ``Person``, which has a ``first_name`` and
+``last_name``::
+    from django.db import models
+    class Person(models.Model):
+        first_name = models.CharField(max_length=30)
+        last_name = models.CharField(max_length=30)
+``first_name`` and ``last_name`` are *fields* of the model. Each field is
+specified as a class attribute, and each attribute maps to a database column.
+The above ``Person`` model would create a database table like this::
+    CREATE TABLE myapp_person (
+        "id" serial NOT NULL PRIMARY KEY,
+        "first_name" varchar(30) NOT NULL,
+        "last_name" varchar(30) NOT NULL
+    );
+Some technical notes:
+    * The name of the table, ``myapp_person``, is automatically derived from
+      some model metadata but can be overridden. See _`Table names` below.
+    * An ``id`` field is added automatically, but this behavior can be
+      overriden. See `Automatic primary key fields`_ below.
+    * The ``CREATE TABLE`` SQL in this example is formatted using PostgreSQL
+      syntax, but it's worth noting Django uses SQL tailored to the database
+      backend specified in your `settings file`_.
+.. _settings file: ../settings/
+Fields
+======
+The most important part of a model -- and the only required part of a model --
+is the list of database fields it defines. Fields are specified by class
+attributes.
+Example::
+    class Musician(models.Model):
+        first_name = models.CharField(max_length=50)
+        last_name = models.CharField(max_length=50)
+        instrument = models.CharField(max_length=100)
+    class Album(models.Model):
+        artist = models.ForeignKey(Musician)
+        name = models.CharField(max_length=100)
+        release_date = models.DateField()
+        num_stars = models.IntegerField()
+Field name restrictions
+-----------------------
+Django places only two restrictions on model field names:
+. A field name cannot be a Python reserved word, because that would result
+       in a Python syntax error. For example::
+           class Example(models.Model):
+               pass = models.IntegerField() # 'pass' is a reserved word!
+. A field name cannot contain more than one underscore in a row, due to
+       the way Django's query lookup syntax works. For example::
+           class Example(models.Model):
+               foo__bar = models.IntegerField() # 'foo__bar' has two underscores!
+These limitations can be worked around, though, because your field name doesn't
+necessarily have to match your database column name. See `db_column`_ below.
+SQL reserved words, such as ``join``, ``where`` or ``select``, *are* allowed as
+model field names, because Django escapes all database table names and column
+names in every underlying SQL query. It uses the quoting syntax of your
+particular database engine.
+Field types
+-----------
+Each field in your model should be an instance of the appropriate ``Field``
+class. Django uses the field class types to determine a few things:
+    * The database column type (e.g. ``INTEGER``, ``VARCHAR``).
+    * The widget to use in Django's admin interface, if you care to use it
+      (e.g. ``<input type="text">``, ``<select>``).
+    * The minimal validation requirements, used in Django's admin and in
+      manipulators.
+Here are all available field types:
+``AutoField``
+~~~~~~~~~~~~~
+An ``IntegerField`` that automatically increments according to available IDs.
+You usually won't need to use this directly; a primary key field will
+automatically be added to your model if you don't specify otherwise. See
+`Automatic primary key fields`_.
+``BooleanField``
+~~~~~~~~~~~~~~~~
+A true/false field.
+The admin represents this as a checkbox.
+``CharField``
+~~~~~~~~~~~~~
+A string field, for small- to large-sized strings.
+For large amounts of text, use ``TextField``.
+The admin represents this as an ``<input type="text">`` (a single-line input).
+``CharField`` has an extra required argument, ``max_length``, the maximum length
+(in characters) of the field. The max_length is enforced at the database level
+and in Django's validation.
+Django veterans: Note that the argument is now called ``max_length`` to
+provide consistency throughout Django. There is full legacy support for
+the old ``maxlength`` argument, but ``max_length`` is prefered.
+``CommaSeparatedIntegerField``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A field of integers separated by commas. As in ``CharField``, the ``max_length``
+argument is required.
+``DateField``
+~~~~~~~~~~~~~
+A date field. Has a few extra optional arguments:
+    ======================  ===================================================
+    Argument                Description
+    ======================  ===================================================
+    ``auto_now``            Automatically set the field to now every time the
+                            object is saved. Useful for "last-modified"
+                            timestamps. Note that the current date is *always*
+                            used; it's not just a default value that you can
+                            override.
+    ``auto_now_add``        Automatically set the field to now when the object
+                            is first created. Useful for creation of
+                            timestamps. Note that the current date is *always*
+                            used; it's not just a default value that you can
+                            override.
+    ======================  ===================================================
+The admin represents this as an ``<input type="text">`` with a JavaScript
+calendar and a shortcut for "Today."
+``DateTimeField``
+~~~~~~~~~~~~~~~~~
+A date and time field. Takes the same extra options as ``DateField``.
+The admin represents this as two ``<input type="text">`` fields, with
+JavaScript shortcuts.
+``DecimalField``
+~~~~~~~~~~~~~~~~
+**New in Django development version**
+A fixed-precision decimal number, represented in Python by a ``Decimal`` instance.
+Has two **required** arguments:
+    ======================  ===================================================
+    Argument                Description
+    ======================  ===================================================
+    ``max_digits``          The maximum number of digits allowed in the number.
+    ``decimal_places``      The number of decimal places to store with the
+                            number.
+    ======================  ===================================================
+For example, to store numbers up to 999 with a resolution of 2 decimal places,
+you'd use::
+    models.DecimalField(..., max_digits=5, decimal_places=2)
+And to store numbers up to approximately one billion with a resolution of 10
+decimal places::
+    models.DecimalField(..., max_digits=19, decimal_places=10)
+The admin represents this as an ``<input type="text">`` (a single-line input).
+``EmailField``
+~~~~~~~~~~~~~~
+A ``CharField`` that checks that the value is a valid e-mail address.
+This doesn't accept ``max_length``; its ``max_length`` is automatically set to
+.
+``FileField``
+~~~~~~~~~~~~~
+A file-upload field. Has one **required** argument:
+    ======================  ===================================================
+    Argument                Description
+    ======================  ===================================================
+    ``upload_to``           A local filesystem path that will be appended to
+                            your ``MEDIA_ROOT`` setting to determine the
+                            output of the ``get_<fieldname>_url()`` helper
+                            function.
+    ======================  ===================================================
+This path may contain `strftime formatting`_, which will be replaced by the
+date/time of the file upload (so that uploaded files don't fill up the given
+directory).
+The admin represents this field as an ``<input type="file">`` (a file-upload
+widget).
+Using a ``FileField`` or an ``ImageField`` (see below) in a model takes a few
+steps:
+. In your settings file, you'll need to define ``MEDIA_ROOT`` as the
+       full path to a directory where you'd like Django to store uploaded
+       files. (For performance, these files are not stored in the database.)
+       Define ``MEDIA_URL`` as the base public URL of that directory. Make
+       sure that this directory is writable by the Web server's user
+       account.
+. Add the ``FileField`` or ``ImageField`` to your model, making sure
+       to define the ``upload_to`` option to tell Django to which
+       subdirectory of ``MEDIA_ROOT`` it should upload files.
+. All that will be stored in your database is a path to the file
+       (relative to ``MEDIA_ROOT``). You'll most likely want to use the
+       convenience ``get_<fieldname>_url`` function provided by Django. For
+       example, if your ``ImageField`` is called ``mug_shot``, you can get
+       the absolute URL to your image in a template with ``{{
+       object.get_mug_shot_url }}``.
+For example, say your ``MEDIA_ROOT`` is set to ``'/home/media'``, and
+``upload_to`` is set to ``'photos/%Y/%m/%d'``. The ``'%Y/%m/%d'`` part of
+``upload_to`` is strftime formatting; ``'%Y'`` is the four-digit year,
+``'%m'`` is the two-digit month and ``'%d'`` is the two-digit day. If you
+upload a file on Jan. 15, 2007, it will be saved in the directory
+``/home/media/photos/2007/01/15``.
+If you want to retrieve the upload file's on-disk filename, or a URL that
+refers to that file, or the file's size, you can use the
+``get_FOO_filename()``, ``get_FOO_url()`` and ``get_FOO_size()`` methods.
+They are all documented here__.
+__ ../db-api/#get-foo-filename
+Note that whenever you deal with uploaded files, you should pay close attention
+to where you're uploading them and what type of files they are, to avoid
+security holes. *Validate all uploaded files* so that you're sure the files are
+what you think they are. For example, if you blindly let somebody upload files,
+without validation, to a directory that's within your Web server's document
+root, then somebody could upload a CGI or PHP script and execute that script by
+visiting its URL on your site. Don't allow that.
+.. _`strftime formatting`: http://docs.python.org/lib/module-time.html#l2h-1941
+``FilePathField``
+~~~~~~~~~~~~~~~~~
+A field whose choices are limited to the filenames in a certain directory
+on the filesystem. Has three special arguments, of which the first is
+**required**:
+    ======================  ===================================================
+    Argument                Description
+    ======================  ===================================================
+    ``path``                Required. The absolute filesystem path to a
+                            directory from which this ``FilePathField`` should
+                            get its choices. Example: ``"/home/images"``.
+    ``match``               Optional. A regular expression, as a string, that
+                            ``FilePathField`` will use to filter filenames.
+                            Note that the regex will be applied to the
+                            base filename, not the full path. Example:
+                            ``"foo.*\.txt$"``, which will match a file called
+                            ``foo23.txt`` but not ``bar.txt`` or ``foo23.gif``.
+    ``recursive``           Optional. Either ``True`` or ``False``. Default is
+                            ``False``. Specifies whether all subdirectories of
+                            ``path`` should be included.
+    ======================  ===================================================
+Of course, these arguments can be used together.
+The one potential gotcha is that ``match`` applies to the base filename,
+not the full path. So, this example::
+    FilePathField(path="/home/images", match="foo.*", recursive=True)
+...will match ``/home/images/foo.gif`` but not ``/home/images/foo/bar.gif``
+because the ``match`` applies to the base filename (``foo.gif`` and
+``bar.gif``).
+``FloatField``
+~~~~~~~~~~~~~~
+**Changed in Django development version**
+A floating-point number represented in Python by a ``float`` instance.
+The admin represents this as an ``<input type="text">`` (a single-line input).
+**NOTE:** The semantics of ``FloatField`` have changed in the Django
+development version. See the `Django 0.96 documentation`_ for the old behavior.
+.. _Django 0.96 documentation: http://www.djangoproject.com/documentation/0.96/model-api/#floatfield
+``ImageField``
+~~~~~~~~~~~~~~
+Like `FileField`_, but validates that the uploaded object is a valid
+image. Has two extra optional arguments, ``height_field`` and
+``width_field``, which, if set, will be auto-populated with the height and
+width of the image each time a model instance is saved.
+In addition to the special ``get_FOO_*`` methods that are available for
+``FileField``, an ``ImageField`` also has ``get_FOO_height()`` and
+``get_FOO_width()`` methods. These are documented elsewhere_.
+Requires the `Python Imaging Library`_.
+.. _Python Imaging Library: http://www.pythonware.com/products/pil/
+.. _elsewhere: ../db-api/#get-foo-height-and-get-foo-width
+``IntegerField``
+~~~~~~~~~~~~~~~~
+An integer.
+The admin represents this as an ``<input type="text">`` (a single-line input).
+``IPAddressField``
+~~~~~~~~~~~~~~~~~~
+An IP address, in string format (i.e. "24.124.1.30").
+The admin represents this as an ``<input type="text">`` (a single-line input).
+``NullBooleanField``
+~~~~~~~~~~~~~~~~~~~~
+Like a ``BooleanField``, but allows ``NULL`` as one of the options.  Use this
+instead of a ``BooleanField`` with ``null=True``.
+The admin represents this as a ``<select>`` box with "Unknown", "Yes" and "No" choices.
+``PhoneNumberField``
+~~~~~~~~~~~~~~~~~~~~
+A ``CharField`` that checks that the value is a valid U.S.A.-style phone
+number (in the format ``XXX-XXX-XXXX``).
+``PositiveIntegerField``
+~~~~~~~~~~~~~~~~~~~~~~~~
+Like an ``IntegerField``, but must be positive.
+``PositiveSmallIntegerField``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Like a ``PositiveIntegerField``, but only allows values under a certain
+(database-dependent) point.
+``SlugField``
+~~~~~~~~~~~~~
+"Slug" is a newspaper term. A slug is a short label for something,
+containing only letters, numbers, underscores, dots, or hyphens. They're generally
+used in URLs.
+Like a CharField, you can specify ``max_length``. If ``max_length`` is
+not specified, Django will use a default length of 50.
+Implies ``db_index=True``.
+Accepts an extra option, ``prepopulate_from``, which is a list of fields
+from which to auto-populate the slug, via JavaScript, in the object's admin
+form::
+    models.SlugField(prepopulate_from=("pre_name", "name"))
+``prepopulate_from`` doesn't accept DateTimeFields, ForeignKeys nor
+ManyToManyFields.
+The admin represents ``SlugField`` as an ``<input type="text">`` (a
+single-line input).
+``SmallIntegerField``
+~~~~~~~~~~~~~~~~~~~~~
+Like an ``IntegerField``, but only allows values under a certain
+(database-dependent) point.
+``TextField``
+~~~~~~~~~~~~~
+A large text field.
+The admin represents this as a ``<textarea>`` (a multi-line input).
+``TimeField``
+~~~~~~~~~~~~~
+A time. Accepts the same auto-population options as ``DateField`` and
+``DateTimeField``.
+The admin represents this as an ``<input type="text">`` with some
+JavaScript shortcuts.
+``URLField``
+~~~~~~~~~~~~
+A field for a URL. If the ``verify_exists`` option is ``True`` (default),
+the URL given will be checked for existence (i.e., the URL actually loads
+and doesn't give a 404 response).
+The admin represents this as an ``<input type="text">`` (a single-line input).
+``URLField`` takes an optional argument, ``max_length``, the maximum length (in
+characters) of the field. The maximum length is enforced at the database level and
+in Django's validation. If you don't specify ``max_length``, a default of 200
+is used.
+``USStateField``
+~~~~~~~~~~~~~~~~
+A two-letter U.S. state abbreviation.
+The admin represents this as an ``<input type="text">`` (a single-line input).
+``XMLField``
+~~~~~~~~~~~~
+A ``TextField`` that checks that the value is valid XML that matches a
+given schema. Takes one required argument, ``schema_path``, which is the
+filesystem path to a RelaxNG_ schema against which to validate the field.
+.. _RelaxNG: http://www.relaxng.org/
+Field options
+-------------
+The following arguments are available to all field types. All are optional.
+``null``
+~~~~~~~~
+If ``True``, Django will store empty values as ``NULL`` in the database.
+Default is ``False``.
+Note that empty string values will always get stored as empty strings, not
+as ``NULL``. Only use ``null=True`` for non-string fields such as integers,
+booleans and dates. For both types of fields, you will also need to set
+``blank=True`` if you wish to permit empty values in forms, as the ``null``
+parameter only affects database storage (see blank_, below).
+Avoid using ``null`` on string-based fields such as ``CharField`` and
+``TextField`` unless you have an excellent reason. If a string-based field
+has ``null=True``, that means it has two possible values for "no data":
+``NULL``, and the empty string. In most cases, it's redundant to have two
+possible values for "no data;" Django convention is to use the empty
+string, not ``NULL``.
+.. note::
+    When using the Oracle database backend, the ``null=True`` option will
+    be coerced for string-based fields that can blank, and the value
+    ``NULL`` will be stored to denote the empty string.
+``blank``
+~~~~~~~~~
+If ``True``, the field is allowed to be blank. Default is ``False``.
+Note that this is different than ``null``. ``null`` is purely
+database-related, whereas ``blank`` is validation-related. If a field has
+``blank=True``, validation on Django's admin site will allow entry of an
+empty value. If a field has ``blank=False``, the field will be required.
+``choices``
+~~~~~~~~~~~
+An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this
+field.
+If this is given, Django's admin will use a select box instead of the
+standard text field and will limit choices to the choices given.
+A choices list looks like this::
+    YEAR_IN_SCHOOL_CHOICES = (
+        ('FR', 'Freshman'),
+        ('SO', 'Sophomore'),
+        ('JR', 'Junior'),
+        ('SR', 'Senior'),
+        ('GR', 'Graduate'),
+    )
+The first element in each tuple is the actual value to be stored. The
+second element is the human-readable name for the option.
+The choices list can be defined either as part of your model class::
+    class Foo(models.Model):
+        GENDER_CHOICES = (
+            ('M', 'Male'),
+            ('F', 'Female'),
+        )
+        gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
+or outside your model class altogether::
+    GENDER_CHOICES = (
+        ('M', 'Male'),
+        ('F', 'Female'),
+    )
+    class Foo(models.Model):
+        gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
+For each model field that has ``choices`` set, Django will add a method to
+retrieve the human-readable name for the field's current value. See
+`get_FOO_display`_ in the database API documentation.
+.. _get_FOO_display: ../db-api/#get-foo-display
+Finally, note that choices can be any iterable object -- not necessarily a
+list or tuple. This lets you construct choices dynamically. But if you find
+yourself hacking ``choices`` to be dynamic, you're probably better off using
+a proper database table with a ``ForeignKey``. ``choices`` is meant for static
+data that doesn't change much, if ever.
+``core``
+~~~~~~~~
+For objects that are edited inline to a related object.
+In the Django admin, if all "core" fields in an inline-edited object are
+cleared, the object will be deleted.
+It is an error to have an inline-editable relation without at least one
+``core=True`` field.
+Please note that each field marked "core" is treated as a required field by the
+Django admin site. Essentially, this means you should put ``core=True`` on all
+required fields in your related object that is being edited inline.
+``db_column``
+~~~~~~~~~~~~~
+The name of the database column to use for this field. If this isn't given,
+Django will use the field's name.
+If your database column name is an SQL reserved word, or contains
+characters that aren't allowed in Python variable names -- notably, the
+hyphen -- that's OK. Django quotes column and table names behind the
+scenes.
+``db_index``
+~~~~~~~~~~~~
+If ``True``, ``django-admin.py sqlindexes`` will output a ``CREATE INDEX``
+statement for this field.
+``db_tablespace``
+~~~~~~~~~~~~~~~~~
+**New in Django development version**
+The name of the database tablespace to use for this field's index, if
+indeed this field is indexed. The default is the ``db_tablespace`` of
+the model, if any. If the backend doesn't support tablespaces, this
+option is ignored.
+``default``
+~~~~~~~~~~~
+The default value for the field.
+``editable``
+~~~~~~~~~~~~
+If ``False``, the field will not be editable in the admin or via form
+processing using the object's ``AddManipulator`` or ``ChangeManipulator``
+classes. Default is ``True``.
+``help_text``
+~~~~~~~~~~~~~
+Extra "help" text to be displayed under the field on the object's admin
+form. It's useful for documentation even if your object doesn't have an
+admin form.
+Note that this value is *not* HTML-escaped when it's displayed in the admin
+interface. This lets you include HTML in ``help_text`` if you so desire. For
+example::
+        help_text="Please use the following format: <em>YYYY-MM-DD</em>."
+``primary_key``
+~~~~~~~~~~~~~~~
+If ``True``, this field is the primary key for the model.
+If you don't specify ``primary_key=True`` for any fields in your model,
+Django will automatically add this field::
+    id = models.AutoField('ID', primary_key=True)
+Thus, you don't need to set ``primary_key=True`` on any of your fields
+unless you want to override the default primary-key behavior.
+``primary_key=True`` implies ``blank=False``, ``null=False`` and
+``unique=True``. Only one primary key is allowed on an object.
+``radio_admin``
+~~~~~~~~~~~~~~~
+By default, Django's admin uses a select-box interface (<select>) for
+fields that are ``ForeignKey`` or have ``choices`` set. If ``radio_admin``
+is set to ``True``, Django will use a radio-button interface instead.
+Don't use this for a field unless it's a ``ForeignKey`` or has ``choices``
+set.
+``unique``
+~~~~~~~~~~
+If ``True``, this field must be unique throughout the table.
+This is enforced at the database level and at the Django admin-form level.
+``unique_for_date``
+~~~~~~~~~~~~~~~~~~~
+Set this to the name of a ``DateField`` or ``DateTimeField`` to require
+that this field be unique for the value of the date field.
+For example, if you have a field ``title`` that has
+``unique_for_date="pub_date"``, then Django wouldn't allow the entry of
+two records with the same ``title`` and ``pub_date``.
+This is enforced at the Django admin-form level but not at the database level.
+``unique_for_month``
+~~~~~~~~~~~~~~~~~~~~
+Like ``unique_for_date``, but requires the field to be unique with respect
+to the month.
+``unique_for_year``
+~~~~~~~~~~~~~~~~~~~
+Like ``unique_for_date`` and ``unique_for_month``.
+``validator_list``
+~~~~~~~~~~~~~~~~~~
+A list of extra validators to apply to the field. Each should be a callable
+that takes the parameters ``field_data, all_data`` and raises
+``django.core.validators.ValidationError`` for errors. (See the
+`validator docs`_.)
+Django comes with quite a few validators. They're in ``django.core.validators``.
+.. _validator docs: ../forms/#validators
+Verbose field names
+-------------------
+Each field type, except for ``ForeignKey``, ``ManyToManyField`` and
+``OneToOneField``, takes an optional first positional argument -- a
+verbose name. If the verbose name isn't given, Django will automatically create
+it using the field's attribute name, converting underscores to spaces.
+In this example, the verbose name is ``"Person's first name"``::
+    first_name = models.CharField("Person's first name", max_length=30)
+In this example, the verbose name is ``"first name"``::
+    first_name = models.CharField(max_length=30)
+``ForeignKey``, ``ManyToManyField`` and ``OneToOneField`` require the first
+argument to be a model class, so use the ``verbose_name`` keyword argument::
+    poll = models.ForeignKey(Poll, verbose_name="the related poll")
+    sites = models.ManyToManyField(Site, verbose_name="list of sites")
+    place = models.OneToOneField(Place, verbose_name="related place")
+Convention is not to capitalize the first letter of the ``verbose_name``.
+Django will automatically capitalize the first letter where it needs to.
+Relationships
+-------------
+Clearly, the power of relational databases lies in relating tables to each
+other. Django offers ways to define the three most common types of database
+relationships: Many-to-one, many-to-many and one-to-one.
+Many-to-one relationships
+~~~~~~~~~~~~~~~~~~~~~~~~~
+To define a many-to-one relationship, use ``ForeignKey``. You use it just like
+any other ``Field`` type: by including it as a class attribute of your model.
+``ForeignKey`` requires a positional argument: the class to which the model is
+related.
+For example, if a ``Car`` model has a ``Manufacturer`` -- that is, a
+``Manufacturer`` makes multiple cars but each ``Car`` only has one
+``Manufacturer`` -- use the following definitions::
+    class Manufacturer(models.Model):
+        # ...
+    class Car(models.Model):
+        manufacturer = models.ForeignKey(Manufacturer)
+        # ...
+To create a recursive relationship -- an object that has a many-to-one
+relationship with itself -- use ``models.ForeignKey('self')``.
+If you need to create a relationship on a model that has not yet been defined,
+you can use the name of the model, rather than the model object itself::
+    class Car(models.Model):
+        manufacturer = models.ForeignKey('Manufacturer')
+        # ...
+    class Manufacturer(models.Model):
+        # ...
+Note, however, that you can only use strings to refer to models in the same
+models.py file -- you cannot use a string to reference a model in a different
+application, or to reference a model that has been imported from elsewhere.
+Behind the scenes, Django appends ``"_id"`` to the field name to create its
+database column name. In the above example, the database table for the ``Car``
+model will have a ``manufacturer_id`` column. (You can change this explicitly
+by specifying ``db_column``; see ``db_column`` below.)  However, your code
+should never have to deal with the database column name, unless you write
+custom SQL. You'll always deal with the field names of your model object.
+It's suggested, but not required, that the name of a ``ForeignKey`` field
+(``manufacturer`` in the example above) be the name of the model, lowercase.
+You can, of course, call the field whatever you want. For example::
+    class Car(models.Model):
+        company_that_makes_it = models.ForeignKey(Manufacturer)
+        # ...
+See the `Many-to-one relationship model example`_ for a full example.
+.. _Many-to-one relationship model example: ../models/many_to_one/
+``ForeignKey`` fields take a number of extra arguments for defining how the
+relationship should work. All are optional:
+    =======================  ============================================================
+    Argument                 Description
+    =======================  ============================================================
+    ``edit_inline``          If not ``False``, this related object is edited
+                             "inline" on the related object's page. This means
+                             that the object will not have its own admin
+                             interface. Use either ``models.TABULAR`` or ``models.STACKED``,
+                             which, respectively, designate whether the inline-editable
+                             objects are displayed as a table or as a "stack" of
+                             fieldsets.
+    ``limit_choices_to``     A dictionary of lookup arguments and values (see
+                             the `Database API reference`_) that limit the
+                             available admin choices for this object. Use this
+                             with functions from the Python ``datetime`` module
+                             to limit choices of objects by date. For example::
+                                limit_choices_to = {'pub_date__lte': datetime.now}
+                             only allows the choice of related objects with a
+                             ``pub_date`` before the current date/time to be
+                             chosen.
+                             Instead of a dictionary this can also be a ``Q`` object
+                             (an object with a ``get_sql()`` method) for more complex
+                             queries.
+                             Not compatible with ``edit_inline``.
+    ``max_num_in_admin``     For inline-edited objects, this is the maximum
+                             number of related objects to display in the admin.
+                             Thus, if a pizza could only have up to 10
+                             toppings, ``max_num_in_admin=10`` would ensure
+                             that a user never enters more than 10 toppings.
+                             Note that this doesn't ensure more than 10 related
+                             toppings ever get created. It simply controls the
+                             admin interface; it doesn't enforce things at the
+                             Python API level or database level.
+    ``min_num_in_admin``     The minimum number of related objects displayed in
+                             the admin. Normally, at the creation stage,
+                             ``num_in_admin`` inline objects are shown, and at
+                             the edit stage ``num_extra_on_change`` blank
+                             objects are shown in addition to all pre-existing
+                             related objects.  However, no fewer than
+                             ``min_num_in_admin`` related objects will ever be
+                             displayed.
+    ``num_extra_on_change``  The number of extra blank related-object fields to
+                             show at the change stage.
+    ``num_in_admin``         The default number of inline objects to display
+                             on the object page at the add stage.
+    ``raw_id_admin``         Only display a field for the integer to be entered
+                             instead of a drop-down menu. This is useful when
+                             related to an object type that will have too many
+                             rows to make a select box practical.
+                             Not used with ``edit_inline``.
+    ``related_name``         The name to use for the relation from the related
+                             object back to this one. See the
+                             `related objects documentation`_ for a full
+                             explanation and example.
+    ``to_field``             The field on the related object that the relation
+                             is to. By default, Django uses the primary key of
+                             the related object.
+    =======================  ============================================================
+.. _`Database API reference`: ../db-api/
+.. _related objects documentation: ../db-api/#related-objects
+Many-to-many relationships
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+To define a many-to-many relationship, use ``ManyToManyField``. You use it just
+like any other ``Field`` type: by including it as a class attribute of your
+model.
+``ManyToManyField`` requires a positional argument: the class to which the
+model is related.
+For example, if a ``Pizza`` has multiple ``Topping`` objects -- that is, a
+``Topping`` can be on multiple pizzas and each ``Pizza`` has multiple toppings --
+here's how you'd represent that::
+    class Topping(models.Model):
+        # ...
+    class Pizza(models.Model):
+        # ...
+        toppings = models.ManyToManyField(Topping)
+As with ``ForeignKey``, a relationship to self can be defined by using the
+string ``'self'`` instead of the model name, and you can refer to as-yet
+undefined models by using a string containing the model name. However, you
+can only use strings to refer to models in the same models.py file -- you
+cannot use a string to reference a model in a different application, or to
+reference a model that has been imported from elsewhere.
+It's suggested, but not required, that the name of a ``ManyToManyField``
+(``toppings`` in the example above) be a plural describing the set of related
+model objects.
+Behind the scenes, Django creates an intermediary join table to represent the
+many-to-many relationship.
+It doesn't matter which model gets the ``ManyToManyField``, but you only need
+it in one of the models -- not in both.
+Generally, ``ManyToManyField`` instances should go in the object that's going
+to be edited in the admin interface, if you're using Django's admin. In the
+above example, ``toppings`` is in ``Pizza`` (rather than ``Topping`` having a
+``pizzas`` ``ManyToManyField`` ) because it's more natural to think about a
+``Pizza`` having toppings than a topping being on multiple pizzas. The way it's
+set up above, the ``Pizza`` admin form would let users select the toppings.
+See the `Many-to-many relationship model example`_ for a full example.
+.. _Many-to-many relationship model example: ../models/many_to_many/
+``ManyToManyField`` objects take a number of extra arguments for defining how
+the relationship should work. All are optional:
+    =======================  ============================================================
+    Argument                 Description
+    =======================  ============================================================
+    ``related_name``         See the description under ``ForeignKey`` above.
+    ``filter_interface``     Use a nifty unobtrusive Javascript "filter" interface
+                             instead of the usability-challenged ``<select multiple>``
+                             in the admin form for this object. The value should be
+                             ``models.HORIZONTAL`` or ``models.VERTICAL`` (i.e.
+                             should the interface be stacked horizontally or
+                             vertically).
+    ``limit_choices_to``     See the description under ``ForeignKey`` above.
+    ``symmetrical``          Only used in the definition of ManyToManyFields on self.
+                             Consider the following model:
+                             class Person(models.Model):
+                                 friends = models.ManyToManyField("self")
+                             When Django processes this model, it identifies that it has
+                             a ``ManyToManyField`` on itself, and as a result, it
+                             doesn't add a ``person_set`` attribute to the ``Person``
+                             class. Instead, the ``ManyToManyField`` is assumed to be
+                             symmetrical -- that is, if I am your friend, then you are
+                             my friend.
+                             If you do not want symmetry in ``ManyToMany`` relationships
+                             with ``self``, set ``symmetrical`` to ``False``. This will
+                             force Django to add the descriptor for the reverse
+                             relationship, allowing ``ManyToMany`` relationships to be
+                             non-symmetrical.
+    ``db_table``             The name of the table to create for storing the many-to-many
+                             data. If this is not provided, Django will assume a default
+                             name based upon the names of the two tables being joined.
+    =======================  ============================================================
+One-to-one relationships
+~~~~~~~~~~~~~~~~~~~~~~~~
+The semantics of one-to-one relationships will be changing soon, so we don't
+recommend you use them. If that doesn't scare you away, keep reading.
+To define a one-to-one relationship, use ``OneToOneField``. You use it just
+like any other ``Field`` type: by including it as a class attribute of your
+model.
+This is most useful on the primary key of an object when that object "extends"
+another object in some way.
+``OneToOneField`` requires a positional argument: the class to which the
+model is related.
+For example, if you're building a database of "places", you would build pretty
+standard stuff such as address, phone number, etc. in the database. Then, if you
+wanted to build a database of restaurants on top of the places, instead of
+repeating yourself and replicating those fields in the ``Restaurant`` model, you
+could make ``Restaurant`` have a ``OneToOneField`` to ``Place`` (because a
+restaurant "is-a" place).
+As with ``ForeignKey``, a relationship to self can be defined by using the
+string ``"self"`` instead of the model name; references to as-yet undefined
+models can be made by using a string containing the model name.
+This ``OneToOneField`` will actually replace the primary key ``id`` field
+(since one-to-one relations share the same primary key), and will be displayed
+as a read-only field when you edit an object in the admin interface:
+See the `One-to-one relationship model example`_ for a full example.
+.. _One-to-one relationship model example: ../models/one_to_one/
+Custom field types
+------------------
+**New in Django development version**
+Django's built-in field types don't cover every possible database column type --
+only the common types, such as ``VARCHAR`` and ``INTEGER``. For more obscure
+column types, such as geographic polygons or even user-created types such as
+`PostgreSQL custom types`_, you can define your own Django ``Field`` subclasses.
+.. _PostgreSQL custom types: http://www.postgresql.org/docs/8.2/interactive/sql-createtype.html
+.. admonition:: Experimental territory
+    This is an area of Django that traditionally has not been documented, but
+    we're starting to include bits of documentation, one feature at a time.
+    Please forgive the sparseness of this section.
+    If you like living on the edge and are comfortable with the risk of
+    unstable, undocumented APIs, see the code for the core ``Field`` class
+    in ``django/db/models/fields/__init__.py`` -- but if/when the innards
+    change, don't say we didn't warn you.
+To create a custom field type, simply subclass ``django.db.models.Field``.
+Here is an incomplete list of the methods you should implement:
+``db_type()``
+~~~~~~~~~~~~~
+Returns the database column data type for the ``Field``, taking into account
+the current ``DATABASE_ENGINE`` setting.
+Say you've created a PostgreSQL custom type called ``mytype``. You can use this
+field with Django by subclassing ``Field`` and implementing the ``db_type()``
+method, like so::
+    from django.db import models
+    class MytypeField(models.Field):
+        def db_type(self):
+            return 'mytype'
+Once you have ``MytypeField``, you can use it in any model, just like any other
+``Field`` type::
+    class Person(models.Model):
+        name = models.CharField(max_length=80)
+        gender = models.CharField(max_length=1)
+        something_else = MytypeField()
+If you aim to build a database-agnostic application, you should account for
+differences in database column types. For example, the date/time column type
+in PostgreSQL is called ``timestamp``, while the same column in MySQL is called
+``datetime``. The simplest way to handle this in a ``db_type()`` method is to
+import the Django settings module and check the ``DATABASE_ENGINE`` setting.
+For example::
+    class MyDateField(models.Field):
+        def db_type(self):
+            from django.conf import settings
+            if settings.DATABASE_ENGINE == 'mysql':
+                return 'datetime'
+            else:
+                return 'timestamp'
+The ``db_type()`` method is only called by Django when the framework constructs
+the ``CREATE TABLE`` statements for your application -- that is, when you first
+create your tables. It's not called at any other time, so it can afford to
+execute slightly complex code, such as the ``DATABASE_ENGINE`` check in the
+above example.
+Some database column types accept parameters, such as ``CHAR(25)``, where the
+parameter ``25`` represents the maximum column length. In cases like these,
+it's more flexible if the parameter is specified in the model rather than being
+hard-coded in the ``db_type()`` method. For example, it wouldn't make much
+sense to have a ``CharMaxlength25Field``, shown here::
+    # This is a silly example of hard-coded parameters.
+    class CharMaxlength25Field(models.Field):
+        def db_type(self):
+            return 'char(25)'
+    # In the model:
+    class MyModel(models.Model):
+        # ...
+        my_field = CharMaxlength25Field()
+The better way of doing this would be to make the parameter specifiable at run
+time -- i.e., when the class is instantiated. To do that, just implement
+``__init__()``, like so::
+    # This is a much more flexible example.
+    class BetterCharField(models.Field):
+        def __init__(self, max_length, *args, **kwargs):
+            self.max_length = max_length
+            super(BetterCharField, self).__init__(*args, **kwargs)
+        def db_type(self):
+            return 'char(%s)' % self.max_length
+    # In the model:
+    class MyModel(models.Model):
+        # ...
+        my_field = BetterCharField(25)
+Note that if you implement ``__init__()`` on a ``Field`` subclass, it's
+important to call ``Field.__init__()`` -- i.e., the parent class'
+``__init__()`` method.
+Meta options
+============
+Give your model metadata by using an inner ``class Meta``, like so::
+    class Foo(models.Model):
+        bar = models.CharField(max_length=30)
+        class Meta:
+            # ...
+Model metadata is "anything that's not a field", such as ordering options, etc.
+Here's a list of all possible ``Meta`` options. No options are required. Adding
+``class Meta`` to a model is completely optional.
+``db_table``
+------------
+The name of the database table to use for the model::
+    db_table = 'music_album'
+If this isn't given, Django will use ``app_label + '_' + model_class_name``.
+See "Table names" below for more.
+If your database table name is an SQL reserved word, or contains characters
+that aren't allowed in Python variable names -- notably, the hyphen --
+that's OK. Django quotes column and table names behind the scenes.
+``db_tablespace``
+-----------------
+**New in Django development version**
+The name of the database tablespace to use for the model. If the backend
+doesn't support tablespaces, this option is ignored.
+``get_latest_by``
+-----------------
+The name of a ``DateField`` or ``DateTimeField`` in the model. This specifies
+the default field to use in your model ``Manager``'s ``latest()`` method.
+Example::
+    get_latest_by = "order_date"
+See the `docs for latest()`_ for more.
+.. _docs for latest(): ../db-api/#latest-field-name-none
+``order_with_respect_to``
+-------------------------
+Marks this object as "orderable" with respect to the given field. This is
+almost always used with related objects to allow them to be ordered with
+respect to a parent object. For example, if an ``Answer`` relates to a
+``Question`` object, and a question has more than one answer, and the order
+of answers matters, you'd do this::
+    class Answer(models.Model):
+        question = models.ForeignKey(Question)
+        # ...
+        class Meta:
+            order_with_respect_to = 'question'
+``ordering``
+------------
+The default ordering for the object, for use when obtaining lists of objects::
+    ordering = ['-order_date']
+This is a tuple or list of strings. Each string is a field name with an
+optional "-" prefix, which indicates descending order. Fields without a
+leading "-" will be ordered ascending. Use the string "?" to order randomly.
+For example, to order by a ``pub_date`` field ascending, use this::
+    ordering = ['pub_date']
+To order by ``pub_date`` descending, use this::
+    ordering = ['-pub_date']
+To order by ``pub_date`` descending, then by ``author`` ascending, use this::
+    ordering = ['-pub_date', 'author']
+See `Specifying ordering`_ for more examples.
+Note that, regardless of how many fields are in ``ordering``, the admin
+site uses only the first field.
+.. _Specifying ordering: ../models/ordering/
+``permissions``
+---------------
+Extra permissions to enter into the permissions table when creating this
+object. Add, delete and change permissions are automatically created for
+each object that has ``admin`` set. This example specifies an extra
+permission, ``can_deliver_pizzas``::
+    permissions = (("can_deliver_pizzas", "Can deliver pizzas"),)
+This is a list or tuple of 2-tuples in the format
+``(permission_code, human_readable_permission_name)``.
+``unique_together``
+-------------------
+Sets of field names that, taken together, must be unique::
+    unique_together = (("driver", "restaurant"),)
+This is a list of lists of fields that must be unique when considered
+together. It's used in the Django admin and is enforced at the database
+level (i.e., the appropriate ``UNIQUE`` statements are included in the
+``CREATE TABLE`` statement).
+``verbose_name``
+----------------
+A human-readable name for the object, singular::
+    verbose_name = "pizza"
+If this isn't given, Django will use a munged version of the class name:
+``CamelCase`` becomes ``camel case``.
+``verbose_name_plural``
+-----------------------
+The plural name for the object::
+    verbose_name_plural = "stories"
+If this isn't given, Django will use ``verbose_name + "s"``.
+Table names
+===========
+To save you time, Django automatically derives the name of the database table
+from the name of your model class and the app that contains it. A model's
+database table name is constructed by joining the model's "app label" -- the
+name you used in ``manage.py startapp`` -- to the model's class name, with an
+underscore between them.
+For example, if you have an app ``bookstore`` (as created by
+``manage.py startapp bookstore``), a model defined as ``class Book`` will have
+a database table named ``bookstore_book``.
+To override the database table name, use the ``db_table`` parameter in
+``class Meta``.
+Automatic primary key fields
+============================
+By default, Django gives each model the following field::
+    id = models.AutoField(primary_key=True)
+This is an auto-incrementing primary key.
+If you'd like to specify a custom primary key, just specify ``primary_key=True``
+on one of your fields. If Django sees you've explicitly set ``primary_key``, it
+won't add the automatic ``id`` column.
+Each model requires exactly one field to have ``primary_key=True``.
+Admin options
+=============
+If you want your model to be visible to Django's admin site, give your model an
+inner ``"class Admin"``, like so::
+    class Person(models.Model):
+        first_name = models.CharField(max_length=30)
+        last_name = models.CharField(max_length=30)
+        class Admin:
+            # Admin options go here
+            pass
+The ``Admin`` class tells Django how to display the model in the admin site.
+Here's a list of all possible ``Admin`` options. None of these options are
+required. To use an admin interface without specifying any options, use
+``pass``, like so::
+    class Admin:
+        pass
+Adding ``class Admin`` to a model is completely optional.
+``date_hierarchy``
+------------------
+Set ``date_hierarchy`` to the name of a ``DateField`` or ``DateTimeField`` in
+your model, and the change list page will include a date-based drilldown
+navigation by that field.
+Example::
+    date_hierarchy = 'pub_date'
+``fields``
+----------
+Set ``fields`` to control the layout of admin "add" and "change" pages.
+``fields`` is a list of two-tuples, in which each two-tuple represents a
+``<fieldset>`` on the admin form page. (A ``<fieldset>`` is a "section" of the
+form.)
+The two-tuples are in the format ``(name, field_options)``, where ``name`` is a
+string representing the title of the fieldset and ``field_options`` is a
+dictionary of information about the fieldset, including a list of fields to be
+displayed in it.
+A full example, taken from the ``django.contrib.flatpages.FlatPage`` model::
+    class Admin:
+        fields = (
+            (None, {
+                'fields': ('url', 'title', 'content', 'sites')
+            }),
+            ('Advanced options', {
+                'classes': 'collapse',
+                'fields' : ('enable_comments', 'registration_required', 'template_name')
+            }),
+        )
+This results in an admin page that looks like:
+    .. image:: http://media.djangoproject.com/img/doc/flatfiles_admin.png
+If ``fields`` isn't given, Django will default to displaying each field that
+isn't an ``AutoField`` and has ``editable=True``, in a single fieldset, in
+the same order as the fields are defined in the model.
+The ``field_options`` dictionary can have the following keys:
+``fields``
+~~~~~~~~~~
+A tuple of field names to display in this fieldset. This key is required.
+Example::
+    {
+    'fields': ('first_name', 'last_name', 'address', 'city', 'state'),
+    }
+To display multiple fields on the same line, wrap those fields in their own
+tuple. In this example, the ``first_name`` and ``last_name`` fields will
+display on the same line::
+    {
+    'fields': (('first_name', 'last_name'), 'address', 'city', 'state'),
+    }
+``classes``
+~~~~~~~~~~~
+A string containing extra CSS classes to apply to the fieldset.
+Example::
+    {
+    'classes': 'wide',
+    }
+Apply multiple classes by separating them with spaces. Example::
+    {
+    'classes': 'wide extrapretty',
+    }
+Two useful classes defined by the default admin-site stylesheet are
+``collapse`` and ``wide``. Fieldsets with the ``collapse`` style will be
+initially collapsed in the admin and replaced with a small "click to expand"
+link. Fieldsets with the ``wide`` style will be given extra horizontal space.
+``description``
+~~~~~~~~~~~~~~~
+A string of optional extra text to be displayed at the top of each fieldset,
+under the heading of the fieldset. It's used verbatim, so you can use any HTML
+and you must escape any special HTML characters (such as ampersands) yourself.
+``js``
+------
+A list of strings representing URLs of JavaScript files to link into the admin
+screen via ``<script src="">`` tags. This can be used to tweak a given type of
+admin page in JavaScript or to provide "quick links" to fill in default values
+for certain fields.
+If you use relative URLs -- URLs that don't start with ``http://`` or ``/`` --
+then the admin site will automatically prefix these links with
+``settings.ADMIN_MEDIA_PREFIX``.
+``list_display``
+----------------
+Set ``list_display`` to control which fields are displayed on the change list
+page of the admin.
+Example::
+    list_display = ('first_name', 'last_name')
+If you don't set ``list_display``, the admin site will display a single column
+that displays the ``__str__()`` representation of each object.
+A few special cases to note about ``list_display``:
+    * If the field is a ``ForeignKey``, Django will display the
+      ``__unicode__()`` of the related object.
+    * ``ManyToManyField`` fields aren't supported, because that would entail
+      executing a separate SQL statement for each row in the table. If you
+      want to do this nonetheless, give your model a custom method, and add
+      that method's name to ``list_display``. (See below for more on custom
+      methods in ``list_display``.)
+    * If the field is a ``BooleanField`` or ``NullBooleanField``, Django will
+      display a pretty "on" or "off" icon instead of ``True`` or ``False``.
+    * If the string given is a method of the model, Django will call it and
+      display the output. This method should have a ``short_description``
+      function attribute, for use as the header for the field.
+      Here's a full example model::
+          class Person(models.Model):
+              name = models.CharField(max_length=50)
+              birthday = models.DateField()
+              class Admin:
+                  list_display = ('name', 'decade_born_in')
+              def decade_born_in(self):
+                  return self.birthday.strftime('%Y')[:3] + "0's"
+              decade_born_in.short_description = 'Birth decade'
+    * If the string given is a method of the model, Django will HTML-escape the
+      output by default. If you'd rather not escape the output of the method,
+      give the method an ``allow_tags`` attribute whose value is ``True``.
+      Here's a full example model::
+          class Person(models.Model):
+              first_name = models.CharField(max_length=50)
+              last_name = models.CharField(max_length=50)
+              color_code = models.CharField(max_length=6)
+              class Admin:
+                  list_display = ('first_name', 'last_name', 'colored_name')
+              def colored_name(self):
+                  return '<span style="color: #%s;">%s %s</span>' % (self.color_code, self.first_name, self.last_name)
+              colored_name.allow_tags = True
+    * If the string given is a method of the model that returns True or False
+      Django will display a pretty "on" or "off" icon if you give the method a
+      ``boolean`` attribute whose value is ``True``.
+      Here's a full example model::
+          class Person(models.Model):
+              first_name = models.CharField(max_length=50)
+              birthday = models.DateField()
+              class Admin:
+                  list_display = ('name', 'born_in_fifties')
+              def born_in_fifties(self):
+                  return self.birthday.strftime('%Y')[:3] == 5
+              born_in_fifties.boolean = True
+    * The ``__str__()`` and ``__unicode__()`` methods are just as valid in
+      ``list_display`` as any other model method, so it's perfectly OK to do
+      this::
+          list_display = ('__unicode__', 'some_other_field')
+    * Usually, elements of ``list_display`` that aren't actual database fields
+      can't be used in sorting (because Django does all the sorting at the
+      database level).
+      However, if an element of ``list_display`` represents a certain database
+      field, you can indicate this fact by setting the ``admin_order_field``
+      attribute of the item.
+      For example::
+        class Person(models.Model):
+            first_name = models.CharField(max_length=50)
+            color_code = models.CharField(max_length=6)
+            class Admin:
+                list_display = ('first_name', 'colored_first_name')
+            def colored_first_name(self):
+                return '<span style="color: #%s;">%s</span>' % (self.color_code, self.first_name)
+            colored_first_name.allow_tags = True
+            colored_first_name.admin_order_field = 'first_name'
+      The above will tell Django to order by the ``first_name`` field when
+      trying to sort by ``colored_first_name`` in the admin.
+``list_display_links``
+----------------------
+Set ``list_display_links`` to control which fields in ``list_display`` should
+be linked to the "change" page for an object.
+By default, the change list page will link the first column -- the first field
+specified in ``list_display`` -- to the change page for each item. But
+``list_display_links`` lets you change which columns are linked. Set
+``list_display_links`` to a list or tuple of field names (in the same format as
+``list_display``) to link.
+``list_display_links`` can specify one or many field names. As long as the
+field names appear in ``list_display``, Django doesn't care how many (or how
+few) fields are linked. The only requirement is: If you want to use
+``list_display_links``, you must define ``list_display``.
+In this example, the ``first_name`` and ``last_name`` fields will be linked on
+the change list page::
+    class Admin:
+        list_display = ('first_name', 'last_name', 'birthday')
+        list_display_links = ('first_name', 'last_name')
+Finally, note that in order to use ``list_display_links``, you must define
+``list_display``, too.
+``list_filter``
+---------------
+Set ``list_filter`` to activate filters in the right sidebar of the change list
+page of the admin. This should be a list of field names, and each specified
+field should be either a ``BooleanField``, ``DateField``, ``DateTimeField``
+or ``ForeignKey``.
+This example, taken from the ``django.contrib.auth.models.User`` model, shows
+how both ``list_display`` and ``list_filter`` work::
+    class Admin:
+        list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff')
+        list_filter = ('is_staff', 'is_superuser')
+The above code results in an admin change list page that looks like this:
+    .. image:: http://media.djangoproject.com/img/doc/users_changelist.png
+(This example also has ``search_fields`` defined. See below.)
+``list_per_page``
+-----------------
+Set ``list_per_page`` to control how many items appear on each paginated admin
+change list page. By default, this is set to ``100``.
+``list_select_related``
+-----------------------
+Set ``list_select_related`` to tell Django to use ``select_related()`` in
+retrieving the list of objects on the admin change list page. This can save you
+a bunch of database queries.
+The value should be either ``True`` or ``False``. Default is ``False``.
+Note that Django will use ``select_related()``, regardless of this setting,
+if one of the ``list_display`` fields is a ``ForeignKey``.
+For more on ``select_related()``, see `the select_related() docs`_.
+.. _the select_related() docs: ../db-api/#select-related
+``ordering``
+------------
+Set ``ordering`` to specify how objects on the admin change list page should be
+ordered. This should be a list or tuple in the same format as a model's
+``ordering`` parameter.
+If this isn't provided, the Django admin will use the model's default ordering.
+``save_as``
+-----------
+Set ``save_as`` to enable a "save as" feature on admin change forms.
+Normally, objects have three save options: "Save", "Save and continue editing"
+and "Save and add another". If ``save_as`` is ``True``, "Save and add another"
+will be replaced by a "Save as" button.
+"Save as" means the object will be saved as a new object (with a new ID),
+rather than the old object.
+By default, ``save_as`` is set to ``False``.
+``save_on_top``
+---------------
+Set ``save_on_top`` to add save buttons across the top of your admin change
+forms.
+Normally, the save buttons appear only at the bottom of the forms. If you set
+``save_on_top``, the buttons will appear both on the top and the bottom.
+By default, ``save_on_top`` is set to ``False``.
+``search_fields``
+-----------------
+Set ``search_fields`` to enable a search box on the admin change list page.
+This should be set to a list of field names that will be searched whenever
+somebody submits a search query in that text box.
+These fields should be some kind of text field, such as ``CharField`` or
+``TextField``. You can also perform a related lookup on a ``ForeignKey`` with
+the lookup API "follow" notation::
+    search_fields = ['foreign_key__related_fieldname']
+When somebody does a search in the admin search box, Django splits the search
+query into words and returns all objects that contain each of the words, case
+insensitive, where each word must be in at least one of ``search_fields``. For
+example, if ``search_fields`` is set to ``['first_name', 'last_name']`` and a
+user searches for ``john lennon``, Django will do the equivalent of this SQL
+``WHERE`` clause::
+    WHERE (first_name ILIKE '%john%' OR last_name ILIKE '%john%')
+    AND (first_name ILIKE '%lennon%' OR last_name ILIKE '%lennon%')
+For faster and/or more restrictive searches, prefix the field name
+with an operator:
+``^``
+    Matches the beginning of the field. For example, if ``search_fields`` is
+    set to ``['^first_name', '^last_name']`` and a user searches for
+    ``john lennon``, Django will do the equivalent of this SQL ``WHERE``
+    clause::
+        WHERE (first_name ILIKE 'john%' OR last_name ILIKE 'john%')
+        AND (first_name ILIKE 'lennon%' OR last_name ILIKE 'lennon%')
+    This query is more efficient than the normal ``'%john%'`` query, because
+    the database only needs to check the beginning of a column's data, rather
+    than seeking through the entire column's data. Plus, if the column has an
+    index on it, some databases may be able to use the index for this query,
+    even though it's a ``LIKE`` query.
+``=``
+    Matches exactly, case-insensitive. For example, if
+    ``search_fields`` is set to ``['=first_name', '=last_name']`` and
+    a user searches for ``john lennon``, Django will do the equivalent
+    of this SQL ``WHERE`` clause::
+        WHERE (first_name ILIKE 'john' OR last_name ILIKE 'john')
+        AND (first_name ILIKE 'lennon' OR last_name ILIKE 'lennon')
+    Note that the query input is split by spaces, so, following this example,
+    it's currently not possible to search for all records in which
+    ``first_name`` is exactly ``'john winston'`` (containing a space).
+``@``
+    Performs a full-text match. This is like the default search method but uses
+    an index. Currently this is only available for MySQL.
+Managers
+========
+A ``Manager`` is the interface through which database query operations are
+provided to Django models. At least one ``Manager`` exists for every model in
+a Django application.
+The way ``Manager`` classes work is documented in the `Retrieving objects`_
+section of the database API docs, but this section specifically touches on
+model options that customize ``Manager`` behavior.
+.. _Retrieving objects: ../db-api/#retrieving-objects
+Manager names
+-------------
+By default, Django adds a ``Manager`` with the name ``objects`` to every Django
+model class. However, if you want to use ``objects`` as a field name, or if you
+want to use a name other than ``objects`` for the ``Manager``, you can rename
+it on a per-model basis. To rename the ``Manager`` for a given class, define a
+class attribute of type ``models.Manager()`` on that model. For example::
+    from django.db import models
+    class Person(models.Model):
+        #...
+        people = models.Manager()
+Using this example model, ``Person.objects`` will generate an
+``AttributeError`` exception, but ``Person.people.all()`` will provide a list
+of all ``Person`` objects.
+Custom Managers
+---------------
+You can use a custom ``Manager`` in a particular model by extending the base
+``Manager`` class and instantiating your custom ``Manager`` in your model.
+There are two reasons you might want to customize a ``Manager``: to add extra
+``Manager`` methods, and/or to modify the initial ``QuerySet`` the ``Manager``
+returns.
+Adding extra Manager methods
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Adding extra ``Manager`` methods is the preferred way to add "table-level"
+functionality to your models. (For "row-level" functionality -- i.e., functions
+that act on a single instance of a model object -- use _`Model methods`, not
+custom ``Manager`` methods.)
+A custom ``Manager`` method can return anything you want. It doesn't have to
+return a ``QuerySet``.
+For example, this custom ``Manager`` offers a method ``with_counts()``, which
+returns a list of all ``OpinionPoll`` objects, each with an extra
+``num_responses`` attribute that is the result of an aggregate query::
+    class PollManager(models.Manager):
+        def with_counts(self):
+            from django.db import connection
+            cursor = connection.cursor()
+            cursor.execute("""
+                SELECT p.id, p.question, p.poll_date, COUNT(*)
+                FROM polls_opinionpoll p, polls_response r
+                WHERE p.id = r.poll_id
+                GROUP BY 1, 2, 3
+                ORDER BY 3 DESC""")
+            result_list = []
+            for row in cursor.fetchall():
+                p = self.model(id=row[0], question=row[1], poll_date=row[2])
+                p.num_responses = row[3]
+                result_list.append(p)
+            return result_list
+    class OpinionPoll(models.Model):
+        question = models.CharField(max_length=200)
+        poll_date = models.DateField()
+        objects = PollManager()
+    class Response(models.Model):
+        poll = models.ForeignKey(Poll)
+        person_name = models.CharField(max_length=50)
+        response = models.TextField()
+With this example, you'd use ``OpinionPoll.objects.with_counts()`` to return
+that list of ``OpinionPoll`` objects with ``num_responses`` attributes.
+Another thing to note about this example is that ``Manager`` methods can
+access ``self.model`` to get the model class to which they're attached.
+Modifying initial Manager QuerySets
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A ``Manager``'s base ``QuerySet`` returns all objects in the system. For
+example, using this model::
+    class Book(models.Model):
+        title = models.CharField(max_length=100)
+        author = models.CharField(max_length=50)
+...the statement ``Book.objects.all()`` will return all books in the database.
+You can override a ``Manager``\'s base ``QuerySet`` by overriding the
+``Manager.get_query_set()`` method. ``get_query_set()`` should return a
+``QuerySet`` with the properties you require.
+For example, the following model has *two* ``Manager``\s -- one that returns
+all objects, and one that returns only the books by Roald Dahl::
+    # First, define the Manager subclass.
+    class DahlBookManager(models.Manager):
+        def get_query_set(self):
+            return super(DahlBookManager, self).get_query_set().filter(author='Roald Dahl')
+    # Then hook it into the Book model explicitly.
+    class Book(models.Model):
+        title = models.CharField(max_length=100)
+        author = models.CharField(max_length=50)
+        objects = models.Manager() # The default manager.
+        dahl_objects = DahlBookManager() # The Dahl-specific manager.
+With this sample model, ``Book.objects.all()`` will return all books in the
+database, but ``Book.dahl_objects.all()`` will only return the ones written by
+Roald Dahl.
+Of course, because ``get_query_set()`` returns a ``QuerySet`` object, you can
+use ``filter()``, ``exclude()`` and all the other ``QuerySet`` methods on it.
+So these statements are all legal::
+    Book.dahl_objects.all()
+    Book.dahl_objects.filter(title='Matilda')
+    Book.dahl_objects.count()
+This example also pointed out another interesting technique: using multiple
+managers on the same model. You can attach as many ``Manager()`` instances to
+a model as you'd like. This is an easy way to define common "filters" for your
+models.
+For example::
+    class MaleManager(models.Manager):
+        def get_query_set(self):
+            return super(MaleManager, self).get_query_set().filter(sex='M')
+    class FemaleManager(models.Manager):
+        def get_query_set(self):
+            return super(FemaleManager, self).get_query_set().filter(sex='F')
+    class Person(models.Model):
+        first_name = models.CharField(max_length=50)
+        last_name = models.CharField(max_length=50)
+        sex = models.CharField(max_length=1, choices=(('M', 'Male'), ('F', 'Female')))
+        people = models.Manager()
+        men = MaleManager()
+        women = FemaleManager()
+This example allows you to request ``Person.men.all()``, ``Person.women.all()``,
+and ``Person.people.all()``, yielding predictable results.
+If you use custom ``Manager`` objects, take note that the first ``Manager``
+Django encounters (in order by which they're defined in the model) has a
+special status. Django interprets the first ``Manager`` defined in a class as
+the "default" ``Manager``. Certain operations -- such as Django's admin site --
+use the default ``Manager`` to obtain lists of objects, so it's generally a
+good idea for the first ``Manager`` to be relatively unfiltered. In the last
+example, the ``people`` ``Manager`` is defined first -- so it's the default
+``Manager``.
+Model methods
+=============
+Define custom methods on a model to add custom "row-level" functionality to
+your objects. Whereas ``Manager`` methods are intended to do "table-wide"
+things, model methods should act on a particular model instance.
+This is a valuable technique for keeping business logic in one place -- the
+model.
+For example, this model has a few custom methods::
+    class Person(models.Model):
+        first_name = models.CharField(max_length=50)
+        last_name = models.CharField(max_length=50)
+        birth_date = models.DateField()
+        address = models.CharField(max_length=100)
+        city = models.CharField(max_length=50)
+        state = models.USStateField() # Yes, this is America-centric...
+        def baby_boomer_status(self):
+            "Returns the person's baby-boomer status."
+            import datetime
+            if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
+                return "Baby boomer"
+            if self.birth_date < datetime.date(1945, 8, 1):
+                return "Pre-boomer"
+            return "Post-boomer"
+        def is_midwestern(self):
+            "Returns True if this person is from the Midwest."
+            return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')
+        def _get_full_name(self):
+            "Returns the person's full name."
+            return '%s %s' % (self.first_name, self.last_name)
+        full_name = property(_get_full_name)
+The last method in this example is a *property*. `Read more about properties`_.
+.. _Read more about properties: http://www.python.org/download/releases/2.2/descrintro/#property
+A few object methods have special meaning:
+``__str__``
+-----------
+``__str__()`` is a Python "magic method" that defines what should be returned
+if you call ``str()`` on the object. Django uses ``str(obj)`` (or the related
+function, ``unicode(obj)`` -- see below) in a number of places, most notably
+as the value displayed to render an object in the Django admin site and as the
+value inserted into a template when it displays an object. Thus, you should
+always return a nice, human-readable string for the object's ``__str__``.
+Although this isn't required, it's strongly encouraged (see the description of
+``__unicode__``, below, before putting ``__str__`` methods everywhere).
+For example::
+    class Person(models.Model):
+        first_name = models.CharField(max_length=50)
+        last_name = models.CharField(max_length=50)
+        def __str__(self):
+            # Note use of django.utils.encoding.smart_str() here because
+            # first_name and last_name will be unicode strings.
+            return smart_str('%s %s' % (self.first_name, self.last_name))
+``__unicode__``
+---------------
+The ``__unicode__()`` method is called whenever you call ``unicode()`` on an
+object. Since Django's database backends will return Unicode strings in your
+model's attributes, you would normally want to write a ``__unicode__()``
+method for your model. The example in the previous section could be written
+more simply as::
+    class Person(models.Model):
+        first_name = models.CharField(max_length=50)
+        last_name = models.CharField(max_length=50)
+        def __unicode__(self):
+            return u'%s %s' % (self.first_name, self.last_name)
+If you define a ``__unicode__()`` method on your model and not a ``__str__()``
+method, Django will automatically provide you with a ``__str__()`` that calls
+``__unicode()__`` and then converts the result correctly to a UTF-8 encoded
+string object. This is recommended development practice: define only
+``__unicode__()`` and let Django take care of the conversion to string objects
+when required.
+``get_absolute_url``
+--------------------
+Define a ``get_absolute_url()`` method to tell Django how to calculate the
+URL for an object. For example::
+    def get_absolute_url(self):
+        return "/people/%i/" % self.id
+Django uses this in its admin interface. If an object defines
+``get_absolute_url()``, the object-editing page will have a "View on site"
+link that will jump you directly to the object's public view, according to
+``get_absolute_url()``.
+Also, a couple of other bits of Django, such as the `syndication feed framework`_,
+use ``get_absolute_url()`` as a convenience to reward people who've defined the
+method.
+.. _syndication feed framework: ../syndication_feeds/
+It's good practice to use ``get_absolute_url()`` in templates, instead of
+hard-coding your objects' URLs. For example, this template code is bad::
+    <a href="/people/{{ object.id }}/">{{ object.name }}</a>
+But this template code is good::
+    <a href="{{ object.get_absolute_url }}">{{ object.name }}</a>
+.. note::
+    The string you return from ``get_absolute_url()`` must contain only ASCII
+    characters (required by the URI spec, `RFC 2396`_) that have been
+    URL-encoded, if necessary. Code and templates using ``get_absolute_url()``
+    should be able to use the result directly without needing to do any
+    further processing. You may wish to use the
+    ``django.utils.encoding.iri_to_uri()`` function to help with this if you
+    are using unicode strings a lot.
+.. _RFC 2396: http://www.ietf.org/rfc/rfc2396.txt
+The ``permalink`` decorator
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The problem with the way we wrote ``get_absolute_url()`` above is that it
+slightly violates the DRY principle: the URL for this object is defined both
+in the URLConf file and in the model.
+You can further decouple your models from the URLconf using the ``permalink``
+decorator. This decorator is passed the view function, a list of positional
+parameters and (optionally) a dictionary of named parameters. Django then
+works out the correct full URL path using the URLconf, substituting the
+parameters you have given into the URL. For example, if your URLconf
+contained a line such as::
+    (r'^people/(\d+)/$', 'people.views.details'),
+...your model could have a ``get_absolute_url`` method that looked like this::
+    from django.db.models import permalink
+    def get_absolute_url(self):
+        return ('people.views.details', [str(self.id)])
+    get_absolute_url = permalink(get_absolute_url)
+Similarly, if you had a URLconf entry that looked like::
+    (r'/archive/(?P<year>\d{4})/(?P<month>\d{1,2})/(?P<day>\d{1,2})/$', archive_view)
+...you could reference this using ``permalink()`` as follows::
+    def get_absolute_url(self):
+        return ('archive_view', (), {
+            'year': self.created.year,
+            'month': self.created.month,
+            'day': self.created.day})
+    get_absolute_url = permalink(get_absolute_url)
+Notice that we specify an empty sequence for the second parameter in this case,
+because we only want to pass keyword parameters, not positional ones.
+In this way, you're tying the model's absolute URL to the view that is used
+to display it, without repeating the URL information anywhere. You can still
+use the ``get_absolute_url`` method in templates, as before.
+Executing custom SQL
+--------------------
+Feel free to write custom SQL statements in custom model methods and
+module-level methods. The object ``django.db.connection`` represents the
+current database connection. To use it, call ``connection.cursor()`` to get a
+cursor object. Then, call ``cursor.execute(sql, [params])`` to execute the SQL
+and ``cursor.fetchone()`` or ``cursor.fetchall()`` to return the resulting
+rows. Example::
+    def my_custom_sql(self):
+        from django.db import connection
+        cursor = connection.cursor()
+        cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
+        row = cursor.fetchone()
+        return row
+``connection`` and ``cursor`` mostly implement the standard `Python DB-API`_
+(except when it comes to `transaction handling`_). If you're not familiar with
+the Python DB-API, note that the SQL statement in ``cursor.execute()`` uses
+placeholders, ``"%s"``, rather than adding parameters directly within the SQL.
+If you use this technique, the underlying database library will automatically
+add quotes and escaping to your parameter(s) as necessary. (Also note that
+Django expects the ``"%s"`` placeholder, *not* the ``"?"`` placeholder, which is
+used by the SQLite Python bindings. This is for the sake of consistency and
+sanity.)
+A final note: If all you want to do is a custom ``WHERE`` clause, you can just
+use the ``where``, ``tables`` and ``params`` arguments to the standard lookup
+API. See `Other lookup options`_.
+.. _Python DB-API: http://www.python.org/peps/pep-0249.html
+.. _Other lookup options: ../db-api/#extra-select-none-where-none-params-none-tables-none
+.. _transaction handling: ../transactions/
+Overriding default model methods
+--------------------------------
+As explained in the `database API docs`_, each model gets a few methods
+automatically -- most notably, ``save()`` and ``delete()``. You can override
+these methods to alter behavior.
+A classic use-case for overriding the built-in methods is if you want something
+to happen whenever you save an object. For example::
+    class Blog(models.Model):
+        name = models.CharField(max_length=100)
+        tagline = models.TextField()
+        def save(self):
+            do_something()
+            super(Blog, self).save() # Call the "real" save() method.
+            do_something_else()
+You can also prevent saving::
+    class Blog(models.Model):
+        name = models.CharField(max_length=100)
+        tagline = models.TextField()
+        def save(self):
+            if self.name == "Yoko Ono's blog":
+                return # Yoko shall never have her own blog!
+            else:
+                super(Blog, self).save() # Call the "real" save() method.
+.. _database API docs: ../db-api/
+Models across files
+===================
+It's perfectly OK to relate a model to one from another app. To do this, just
+import the related model at the top of the model that holds your model. Then,
+just refer to the other model class wherever needed. For example::
+    from mysite.geography.models import ZipCode
+    class Restaurant(models.Model):
+        # ...
+        zip_code = models.ForeignKey(ZipCode)
+Using models
+============
+Once you have created your models, the final step is to tell Django you're
+going to *use* those models.
+Do this by editing your settings file and changing the ``INSTALLED_APPS``
+setting to add the name of the module that contains your ``models.py``.
+For example, if the models for your application live in the module
+``mysite.myapp.models`` (the package structure that is created for an
+application by the ``manage.py startapp`` script), ``INSTALLED_APPS`` should
+read, in part::
+    INSTALLED_APPS = (
+        #...
+        'mysite.myapp',
+        #...
+    )
+Providing initial SQL data
+==========================
+Django provides a hook for passing the database arbitrary SQL that's executed
+just after the CREATE TABLE statements. Use this hook, for example, if you want
+to populate default records, or create SQL functions, automatically.
+The hook is simple: Django just looks for a file called
+``<appname>/sql/<modelname>.sql``, where ``<appname>`` is your app directory and
+``<modelname>`` is the model's name in lowercase.
+In the ``Person`` example model at the top of this document, assuming it lives
+in an app called ``myapp``, you could add arbitrary SQL to the file
+``myapp/sql/person.sql``. Here's an example of what the file might contain::
+    INSERT INTO myapp_person (first_name, last_name) VALUES ('John', 'Lennon');
+    INSERT INTO myapp_person (first_name, last_name) VALUES ('Paul', 'McCartney');
+Each SQL file, if given, is expected to contain valid SQL. The SQL files are
+piped directly into the database after all of the models' table-creation
+statements have been executed.
+The SQL files are read by the ``sqlcustom``, ``sqlreset``, ``sqlall`` and
+``reset`` commands in ``manage.py``. Refer to the `manage.py documentation`_
+for more information.
+Note that if you have multiple SQL data files, there's no guarantee of the
+order in which they're executed. The only thing you can assume is that, by the
+time your custom data files are executed, all the database tables already will
+have been created.
+.. _`manage.py documentation`: ../django-admin/#sqlcustom-appname-appname
+Database-backend-specific SQL data
+----------------------------------
+There's also a hook for backend-specific SQL data. For example, you can have
+separate initial-data files for PostgreSQL and MySQL. For each app, Django
+looks for a file called ``<appname>/sql/<modelname>.<backend>.sql``, where
+``<appname>`` is your app directory, ``<modelname>`` is the model's name in
+lowercase and ``<backend>`` is the value of ``DATABASE_ENGINE`` in your
+settings file (e.g., ``postgresql``, ``mysql``).
+Backend-specific SQL data is executed before non-backend-specific SQL data. For
+example, if your app contains the files ``sql/person.sql`` and
+``sql/person.postgresql.sql`` and you're installing the app on PostgreSQL,
+Django will execute the contents of ``sql/person.postgresql.sql`` first, then
+``sql/person.sql``.

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