Add GeoJSON support for geometry fields in django-tastypie

tastyhacks.py

# Shamelessly stolen from https://github.com/newsapps/django-boundaryservice/blob/master/boundaryservice/tastyhacks.py

from django.contrib.gis.db.models import GeometryField
from django.utils import simplejson

from tastypie.bundle import Bundle
from tastypie.fields import ApiField, CharField
from tastypie.resources import ModelResource


class GeometryApiField(ApiField):
    """
    Custom ApiField for dealing with data from GeometryFields (by serializing them as GeoJSON).
    """
    dehydrated_type = 'geometry'
    help_text = 'Geometry data.'

    def hydrate(self, bundle):
        value = super(GeometryApiField, self).hydrate(bundle)
        if value is None:
            return value
        return simplejson.dumps(value)
    
    def dehydrate(self, obj):
        return self.convert(super(GeometryApiField, self).dehydrate(obj))
    
    def convert(self, value):
        if value is None:
            return None

        if isinstance(value, dict):
            return value

        # Get ready-made geojson serialization and then convert it _back_ to a Python object
        # so that Tastypie can serialize it as part of the bundle
        return simplejson.loads(value.geojson)


class GeoResource(ModelResource):
    """
    ModelResource subclass that handles geometry fields as GeoJSON.
    """

    @classmethod
    def api_field_from_django_field(cls, f, default=CharField):
        """
        Overrides default field handling to support custom GeometryApiField.
        """
        if isinstance(f, GeometryField):
            return GeometryApiField
    
        return super(GeoResource, cls).api_field_from_django_field(f, default)

I am trying to use this code, it works fine, however do you have an idea why the coordinates are getting stripped down to 10 characters?

Also, how do I POST/PUT/PATCH to the GeometryApiField? I tried the same data that was returned by GET, but I am getting ``cannot set Order GeometryProxy with value of type: dict` exception

so, whoever needs to POST/PUT/PATCH on GeometryApiField, add the following method into the GeometryApiField:

    def hydrate(self, bundle):
        value = super(GeometryApiField, self).hydrate(bundle)
        return simplejson.dumps(value)

excellent, thanks! will try it in an upcoming project.

here's a little bugfix for a case when value is None:

    def hydrate(self, bundle):
        value = super(GeometryApiField, self).hydrate(bundle)
        if value is None:
            return value
        return simplejson.dumps(value)

This seems to work great! I've started a tastypie branch to work on geo-related stuff. The idea is you'd be able to do something like:

from tastypie.contrib.gis.resources import ModelResource

class MyResource(ModelResource):
 ...

which would be more in line with how Django handles gis stuff in general. I think this should be included in tastypie, but if not we can break off into a separate tastypie-contrib repository.

this seems like a good approach. did you discuss this with tastypie maintainers or post a pull request?

I will issue a pull request once I'm satisfied that my branch is working right. And once I have tests + docs :)