Changes between Version 6 and Version 7 of GeoDjangoModelAPI


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Timestamp:
Sep 3, 2008, 9:00:51 PM (17 years ago)
Author:
jbronn
Comment:

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  • GeoDjangoModelAPI

    v6 v7  
    1 [[TOC]]
    2 = Model API =
    3 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:
    4 {{{
    5 #!python
    6 from django.contrib.gis.db import models
     1The !GeoDjango Model API documentation is now located at [http://geodjango.org/docs/model-api.html geodjango.org]
    72
    8 class Zip(models.Model):
    9   code = models.CharField(maxlength=5)
    10   poly = models.PolygonField()
    11 
    12   objects = models.GeoManager()
    13 }}}
    14 
    15 == Field Types ==
    16 
    17 The following geometry-enabled fields are available:
    18  * {{{PointField}}}
    19  * {{{LineStringField}}}
    20  * {{{PolygonField}}}
    21  * {{{MultiPointField}}}
    22  * {{{MultiLineStringField}}}
    23  * {{{MultiPolygonField}}}
    24  * {{{GeometryCollectionField}}}
    25 
    26 Each of these fields correspond with OpenGIS [http://en.wikipedia.org/wiki/Simple_Features Simple Features]. 
    27 
    28 == Field Options ==
    29 
    30 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:
    31  * `srid`
    32    * 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).
    33  * `spatial_index`
    34    * 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.  The original keyword, `index`, has been deprecated and will disappear in future revisions.
    35 
    36 == !GeoManager ==
    37 
    38 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:
    39 {{{
    40 #!python
    41 from django.contrib.gis.db import models
    42 
    43 class Address(models.Model):
    44     num = models.IntegerField()
    45     street = models.CharField(maxlength=100)
    46     city = models.CharField(maxlength=100)
    47     state = models.USStateField()
    48     zip = models.ForeignKey(Zip)
    49 
    50     objects = models.GeoManager()
    51 }}}
    52 
    53 The geographic manager is needed to do spatial queries on [http://www.djangoproject.com/documentation/db-api/#related-objects related Zip objects], for example:
    54 {{{
    55 >>> qs = Address.objects.filter(zip__poly__contains='POINT(-104.590948 38.319914)')
    56 }}}
    57 
    58 
    59 == !GeoMixin ==
    60 
    61 '''Update:''' The [http://code.djangoproject.com/browser/django/branches/gis/django/contrib/gis/db/models/GeoMixin.py GeoMixin] is no longer necessary for geographic models as of r6467.  The mixin used to provide extra instance methods ([wiki:GeoDjangoDatabaseAPI#ExtraInstanceMethods discussed in the database api docs]) for geographic models without subclassing (aka ModelInheritance) -- which is not yet functional in Django.
     3Feel free to leave comments and/or suggestions about the !GeoDjango Model API documentation here.
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