How to JSON-serialize a dictionary that contains a Django PointField? [duplicate] - json

Question

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Rendering spatial data of GeoQuerySet in a custom view on GeoDjango
(1 answer)
Closed 2 years ago.
I am in the process of building a website on geodjango. On the front end I have a map on openlayers and I want to be able to fire ajax queries at some django url and get back geojson.
The problem is that the standard django json serializer doesn't do geojson. So I have a model like:
class Asset (models.Model):
objects = models.GeoManager()
url_name = models.CharField(max_length=200)
name = models.CharField(max_length=200)
point = models.PointField(srid=4326)
def __unicode__(self):
return self.name
And I want to create a view:
def geojson_query(request):
#geographic query
...
assets = Asset.objects.all().filter(point__contained=bb_4326)
json = serializers.serialize("json", assets)
return HttpResponse(json)
But then I get back a response that looks more like this:
"url_name": "Upper_Svaneti",
"name": "Upper Svaneti",
"point": "POINT (43.0113899999999987 42.9163899999999998)"
Whereas I want something that looks like this:
"url_name": "Upper_Svaneti",
"name": "Upper Svaneti",
"geometry": {
"type": "Point",
"coordinates": [43.0113899999999987 42.9163899999999998]
}
So I guess my question is, what is the best way to implement a geojson serializer in django without totally rolling my own? And if it comes to rolling my own, where do I start?

Answer 1

You need to write your own serializer. Just inherit from the DjangoJSONEncoder, here's one I created that supports the Point type:
from django.core.serializers.json import DjangoJSONEncoder
from django.contrib.gis.geos import Point
class GeoJSONEncoder(DjangoJSONEncoder):
def default(self, obj):
if isinstance(obj, Point):
return obj.coords
return super(GeoJSONEncoder, self).default(obj)
You can then use it like so:
from my_app.serializers import GeoJSONEncoder
from django.utils import simplejson
json = simplejson.dumps(data, cls=GeoJSONEncoder)

Answer 2

So... I have done something slightly unpretty. I hardcoded the non-geojson parts of the serializer and used the json function from GEOS to get the geojson part.
So the method in the model looks like:
def get_footprint_json(self):
geojson=self.footprint.json
json='{"type": "Feature","geometry": %s,"properties": {"name":"%s","url_name":"%s"}}'%(geojson,self.name,self.url_name)
return json
And... I have a view that looks like this:
json='{ "srid":4326, "type": "FeatureCollection","features": ['+','.join([asset.get_footprint_json() for asset in assets])+'] }'
return HttpResponse(json)
I'd be curious to see if anyone else has a better way or if django has updated their serializer to include geojson.