Changes between Initial Version and Version 1 of GeoDjangoModelAPI

Timestamp:

Jun 2, 2007, 10:33:12 PM (18 years ago)

Author:

jbronn

Comment:

added GeoDjango model api

GeoDjangoModelAPI

@@ +1 @@
+[[TOC]]
+= Model API =
+This section explores the details of the GeoDjango Model API.  Throughout this section, we'll be using the following geographic model of a Zip code as our example:
+{{{
+#!python
+from django.contrib.gis.db import models
+
+class Zip(models.Model, models.GeoMixin):
+  code = models.CharField(maxlength=5)
+  poly = models.PolygonField()
+
+  object = models.GeoManager()
+}}}
+
+== Field Types ==
+
+The following geometry-enabled fields are available:
+ * {{{PointField}}}
+ * {{{LineStringField}}}
+ * {{{PolygonField}}}
+ * {{{MultiPointField}}}
+ * {{{MultiLineStringField}}}
+ * {{{MultiPolygonField}}}
+ * {{{GeometryCollectionField}}}
+
+Each of these fields correspond with OpenGIS [http://en.wikipedia.org/wiki/Simple_Features Simple Features].  
+
+== Field Options ==
+
+In addition to the regular [http://www.djangoproject.com/documentation/model-api/#field-options field options] available for Django models, Geographic-enabled models have  the following additional options:
+ * {{{srid}}}
+   * Sets the SRID (Spatial Reference System Identity) of geometry to the given value.  Defaults to 4326 (WGS84).  ''See'' Open GIS Consortium, Inc., ''[http://www.opengis.org/docs/99-049.pdf OpenGIS Simple Feature Specification For SQL]'', Document 99-049 (May 5, 1999), at  Ch. 2.3.8 (Geometry Values and Spatial Reference Systems, pg. 39).
+ * {{{index}}}
+   * Defaults to True.  Creates a GiST index for the given geometry.  Update the index with the PostgreSQL command {{{VACUUM ANALYZE}}} (may take a while to execute depending on how large your geographic-enabled tables are).  Please note that this is different from the {{{db_index}}} field option since geographic indexes are created in a different manner than regular indexes.
+
+== GeoMixin ==
+
+The [http://code.djangoproject.com/browser/django/branches/gis/django/contrib/gis/db/models/GeoMixin.py GeoMixin] is necessary for all geographic-enabled models.  The mixin provides extra instance methods (discussed in the database api docs) for geographic models without subclassing (aka ModelInheritance) -- which is not yet functional in Django.
+
+== GeoManager ==
+
+In order to conduct geographic queries, each geographic model requires {{{GeoManager}}}.  This [http://www.djangoproject.com/documentation/model-api/#managers manager] allows for the proper SQL construction for geographic queries; thus, without it, all geographic filters will fail.  It should also be noted that a {{{GeoManager}}} will be required even if the model does not have a geographic field itself, ''i.e.'',in the case of a {{{ForeignKey}}} to a geographic model.  For example, if we had an {{{Address}}} model with a {{{ForeignKey}}} to our {{{Zip}}} geographic model:
+{{{
+#!python
+from django.contrib.gis.db import models
+
+class Address(models.Model):
+    num = models.IntegerField()
+    street = models.CharField(maxlength=100)
+    city = models.CharField(maxlength=100)
+    state = models.USStateField()
+    zip = models.ForeignKey(Zip)
+
+    objects = models.GeoManager()
+}}}
+
+The geographic manager is needed to do spatial queries on [http://www.djangoproject.com/documentation/db-api/#related-objects related Zip objects], for example:
+{{{
+>>> qs = Address.objects.filter(zip__poly__contains='POINT(-104.590948 38.319914)')
+}}}