Removing the magic

The "magic-removal" branch aims to make several sweeping changes to the Django codebase, removing warts that Django has accumulated over the years. Most changes involve the database API and removing some of its unneeded magic, and other changes involve improving the framework's simplicity and usability.

These changes will be integrated into the next Django release, 0.92.

This document explains the changes in the branch.

How to get the branch

Play with it! The branch is available via Subversion at ​http://code.djangoproject.com/svn/django/branches/magic-removal .

Models support properties

Status: Done

Unlike before, properties are supported on models.

from django.db import models

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)

    def _get_full_name(self):
        return "%s %s" % (self.first_name, self.last_name)
    full_name = property(_get_full_name)

Model class and Field classes renamed/relocated

Status: Done

Difference: Import is from django.db.models instead of django.core.meta. This is easier to remember.

from django.db import models

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)

Database connection relocated/renamed

Status: Done

The connection is now available at django.db.connection. This is easier to remember, clearer and more consistent.

Old:

from django.core.db import db
cursor = db.cursor()

New:

from django.db import connection
cursor = connection.cursor()

Backend-specific functions, if you should need them, are available at django.db.backend.

Old:

from django.core import db
db.quote_name('foo')

New:

from django.db import backend
backend.quote_name('foo')

Also, the various backend functionality has been split into three separate modules for each backend -- base.py, creation.py and introspection.py. This is purely for performance and memory savings, so that basic, everyday Django usage doesn't have to load the introspective functionality into memory.

Interact directly with model classes, not with magic modules

Status: Done

Import the model class directly from the module in which it was defined. No more django.models.* magic.

from myproject.people.models import Person
p = Person(first_name='John', last_name='Smith')
p.save()

This also removes the need for the module_name parameter.

Access table-level DB API functions via model classes, not with magic modules

Status: Done

All "table-level" functions -- ways of retrieving records tablewide rather than performing instance-specific tasks -- are now accessed via a model class's objects attribute. They aren't direct methods of a model instance object because we want to keep the "table-wide" and "row-specific" namespaces separate.

from myproject.people.models import Person
p_list = Person.objects.get_list()
p = Person.objects.get_object()

This doesn't work from an instance.

p = Person.objects.get_object(pk=1)
p.objects.get_list() # Raises AttributeError

Override default manager name ("objects")

Status: Done

If a model already has an objects attribute, you'll need to specify an alternate name for the magic objects.

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)
    objects = models.TextField()
    people = models.Manager()

p = Person(first_name='Mary', last_name='Jones', objects='Hello there.')
p.save()
p.objects == 'Hello there.'
Person.people.get_list()

Custom managers, and multiple managers

Status: Done

You can create as many managers as you want. When necessary (such as on the admin), Django will use the first one defined, in order.

If you define at least one custom manager, it will not get the default "objects" manager.

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)
    people = models.Manager()
    fun_people = SomeOtherManager()

Added a more powerful way of overriding model methods, removed hard-coded _pre_save(), _post_save(), etc.

Status: Done

Proper subclassing of methods now works, so you can subclass the automatic save() and delete() methods. This removes the need for the _pre_save(), _post_save(), _pre_delete() and _post_delete() hooks -- all of which have been removed. Example:

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)

    def save(self):
        self.do_something()
        super(Person, self).save() # Call the "real" save() method.
        self.do_something_else()

You can even skip saving (as requested in #1014).

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)

    def save(self):
        if datetime.date.today() > datetime.date(2005, 1, 1):
            super(Person, self).save() # Call the "real" save() method.
        else:
            # Don't save.
            pass

New API functionality: Overriding table-level functions

Status: Done

You can override any table-level functions, such as get_list() or get_object(). Do this by creating a custom models.Manager subclass and passing it to your model.

from django.db import models
class PersonManager(models.Manager):
    def get_list(self, **kwargs):
        # Changes get_list() to hard-code a limit=10.
        kwargs['limit'] = 10
        return models.Manager.get_list(self, **kwargs) # Call the "real" get_list() method.

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)
    objects = PersonManager()

If a manager needs to access its associated class, it should use self.klass. Example:

class PersonManager(models.Manager):
    def get_fun_person(self):
        try:
            return self.get_object(fun__exact=True)
        except self.klass.DoesNotExist:
            print "Doesn't exist."

An alternative syntax for this is proposed in #1224.

Renamed DoesNotExist exception

Status: Done

Instead of people.PersonDoesNotExist, it's Person.DoesNotExist.

Old:

from django.models.myapp import people
try:
    people.get_object(pk=1)
except people.PersonDoesNotExist:
    print "Not there"

New:

from path.to.myapp.models import Person
try:
    Person.objects.get_object(pk=1)
except Person.DoesNotExist:
    print "Not there"

Removed SilentVariableFailure exception

Status: Done

Old behavior: Any exception that subclasses django.core.template.SilentVariableFailure fails silently in the template system.

New behavior: Any exception that has a silent_variable_failure attribute fails silently in the template system. django.core.template.SilentVariableFailure no longer exists.

Automatic manipulators

Status: Mostly done, with some quirks left

Old:

from django.models.myapp import people
m1 = people.AddManipulator()
m2 = people.ChangeManipulator(3)

New:

from path.to.myapp.models import Person
m1 = Person.AddManipulator()
m2 = Person.ChangeManipulator(3)

Renamed 'class META' to 'class Meta'

Status: Done

The class META within models should now be class Meta. The latter is nicer on the eyes.

Moved admin options to 'class Admin'

Status: Done

Instead of admin=meta.Admin in the class META, all admin options are in an inner class Admin.

Old:

class Person(meta.Model):
    first_name = meta.CharField(maxlength=30)
    last_name = meta.CharField(maxlength=30)
    class META:
        admin = meta.Admin(
            list_display = ('first_name', 'last_name')
        )

New:

class Person(models.Model):
    first_name = models.CharField(maxlength=30)
    last_name = models.CharField(maxlength=30)
    class Admin:
        list_display = ('first_name', 'last_name')

get_object_or_404 and get_list_or_404 now take model classes, not modules

Status: Done

Old:

get_object_or_404(polls, pk=1)

New:

get_object_or_404(Poll, pk=1)

Model methods no longer automatically have access to datetime and db modules

Status: Done

Formerly, each model method magically had access to the datetime module and to the variable db, which represents the current database connection. Now, those have to be imported explicitly.

Old:

    def some_method(self):
        print datetime.datetime.now()
        cursor = db.cursor()
        cursor.execute("UPDATE something;")

New:

import datetime
from django.db import connection

# ...

    def some_method(self):
        print datetime.datetime.now()
        cursor = connection.cursor()
        cursor.execute("UPDATE something;")

Moved "auth" and "core" models to django.contrib

Status: Done

See ​http://groups.google.com/group/django-developers/browse_thread/thread/276d071a74543448/7d4b1c40c2d53393

• Old: django.models.auth
• New: django.contrib.auth.models

• Old: django.models.core.sites
• New: django.contrib.sites.models

• Old: django.models.core.contenttypes
• New: django.contrib.contenttypes.models

• Old: django.models.core.packages
• New: django.contrib.contenttypes.models ("Packages" will most likely be removed in the future.)

Moved Session model and middleware from core to django.contrib

Status: Done

The location of the session middleware has changed.

• Old: django.middleware.sessions.SessionMiddleware
• New: django.contrib.sessions.middleware.SessionMiddleware

Make sure to update your MIDDLEWARE_CLASSES setting, if you're using sessions.

Also, the Session model has moved from django/models/core.py to django/contrib/sessions/models.py. If you're accessing the Session model for some reason, note that location change.

Changed the parameters you pass to generic views

Status: Done

Because there's no longer a concept of module_name, the "info_dicts" passed to ​generic views no longer accept "app_label" and "module_name". Instead, pass the parameter "model", which should be your model class.

These examples assume models live in myproject/blog/models.py.

Old:

info_dict = {
    'app_label': 'blog',
    'module_name': 'entries'
}

New:

from myproject.blog.models import Entry
info_dict = {
    'model': Entry
}

Changed template names in generic views

Status: Done

Because there's no longer a concept of module_name, ​generic views no longer create templates based on the module_name. Wherever they used module_name, they now use model_name, a lowercase version of the model name.

Note that app_label remains the same.

These examples assume models live in myproject/blog/models.py.

• Old: blog/entries_archive.html
• New: blog/entry_archive.html

Moved admin URLconf to shorten its path

Status: Done

• Old: django.contrib.admin.urls.admin
• New: django.contrib.admin.urls

Moved settings into an instance

Status: Done

To make it easier to switch settings in situations where you would need multiple different settings - for example when trying to use multiple django projects within one server context or when using Django apps within a bigger WSGI scenario - the settings were moved out of a dedicated module django.conf.settings into an instance in the django.conf module. So now you need to import the settings object and reference settings as attributes of that instance.

Wrappers around the Django machinery can make use of this by exchanging the settings instance with a proxy instance that delegates attribute access to a per-thread or per-location global.

• Old: from django.conf.settings import LANGUAGE_CODE
• New: from django.conf import settings

Database table-name changes

Renamed core_sessions table to django_sessions. To change, execute this SQL in your database:

ALTER TABLE core_sessions RENAME TO django_sessions;

Change subclassing syntax

Status: Not done yet

Database lookup API changes

Status: Not done yet

See DescriptorFields, rjwittams' proposal on the API changes.

Namespace Simplification

Status: Done

See NamespaceSimplification for details.