Generalizing Polygons to MultiPolygons in GeoDjango?
The SQL to drop the constraint:
ALTER TABLE myapp_mymodel DROP CONSTRAINT enforce_geotype_mygeom;
Or to alter it to allow both Polygons & MultiPolygons:
ALTER TABLE myapp_mymodel DROP CONSTRAINT enforce_geotype_mygeom;
ALTER TABLE myapp_mymodel ADD CONSTRAINT enforce_geotype_mygeom CHECK (geometrytype(mygeom) = 'POLYGON'::text OR geometrytype(mygeom) = 'MULTIPOLYGON'::text OR mygeom IS NULL);
These SQL statements could be run from a South migration or an initial-data SQL script.
Another option is to make it a GeometryField
in your Django model definition - this will allow it to store any geometry type.
Or, override the save()
method on your model to force everything to be a MultiPolygon:
from django.contrib.gis.db import models
from django.contrib.gis import geos
class MyModel(models.Model):
mygeom = models.MultiPolygonField()
... other fields....
def save(self, *args, **kwargs):
# if mygeom ends up as a Polgon, make it into a MultiPolygon
if self.mygeom and isinstance(self.mygeom, geos.Polygon):
self.mygeom = geos.MultiPolygon(self.mygeom)
super(MyModel).save(*args, **kwargs)
I know this is old, but I just ran into this issue myself and had problems using the above suggested solutions:
Using
GeometryField
makes it difficult to use the built-inOSMGeoAdmin
class. The code intemplates/gis/admin/openlayers.js
(andcontrib/gis/admin/widgets.py
and probably other places I missed) frequently assumes that the geometry is a point, line, polygon, or collection, and never accounts for generic geometries. This isn't necessarily important or insurmountable, but if you were planning on using the built-in admin you might be disappointed.Overriding
save()
doesn't work because the type-checking happens sooner, in the model's__set__()
.
My current solution is explicitly coercing all of my Polygon
s into MultiPolygon
s when importing and saving my data. I might override __set__()
if this becomes cumbersome.
longish workaround
one could use fromstr()
from django.contrib.gis.geos import fromstr
p = Polygon()
# this seems to work correctly
mp = MultiPolygon(fromstr(str(p)),)
model1.geom_field = mp
model1.save()