django django-rest-framework geojson geodjango django-rest-framework-gis

Error when serializing foreign key object with django-rest-framework-gis to geojson

I am trying to serialize into geojson a model with a foreign key that has a geometry field. I am using the django-rest-framework-gis. I am using django 2.2

I'm stuck on this and none of the other related answers on Stack Overflow work for me. e.g. I have tried versions of this:

The problem is I get this error: Expected a Response, HttpResponse or HttpStreamingResponse to be returned from the view, but received a <class 'statements.models.Response'>

Models:

from django.contrib.gis.db import models
from django.contrib.gis.geos import Point

class Hexgrid_10km2(models.Model):
    lng = models.FloatField()
    lat = models.FloatField()
    polygon = models.MultiPolygonField(srid=4326)
    centroid = models.PointField(default=Point(0,0), srid=4326)

    def __str__(self):
        return f'lng: { self.lng } lat: {self.lat }'


class Response(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    statement = models.ForeignKey(Statement, on_delete=models.CASCADE)
    hexgrid_10km2 = models.ForeignKey(Hexgrid_10km2, on_delete=models.CASCADE, null=True, blank=True)

    @property
        def polygon(self):
            return self.hexgrid_10km2.polygon

Views

class ResponseHeatmapAPIView(APIView): #ReadOnly

    def get(self, request, pk):
        final = Response.objects.all()
        serializer = ResponseHeatmapSerializer(final, many=True)
        return Response(serializer.data)

Serializers

class ResponseHeatmapSerializer(GeoFeatureModelSerializer):
    """ A class to serialize hex polygons as GeoJSON compatible data """

    hexgrid_10km2 = GeometrySerializerMethodField()

    def get_hexgrid_10km2(self, obj):
        return obj.hexgrid_10km2.polygon

    class Meta:
        model = Response
        geo_field = 'hexgrid_10km2'
        id_field = False
        fields = ('id',)

Traceback

OrderedDict([('type', 'FeatureCollection'), ('features', [OrderedDict([('id', 2), ('type', 'Feature'), ('geometry', GeoJsonDict([('type', 'MultiPolygon'), ('coordinates', [[[[0.52353663711945, 50.8631481850499], [0.538799411254891, 50.86870974483], [0.554062185390241, 50.8631481850499], [0.554062185390241, 50.852023074998], [0.548895002474644, 50.85013962], [0.540831980000019, 50.85013962], [0.53199000192362, 50.8489417564374], [0.52353663711945, 50.852023074998], [0.52353663711945, 50.8631481850499]]]])])), ('properties', OrderedDict([('response_date', '2020-04-15T21:04:04.599597Z'), ('agree', 1), ('hasLocation', False), ('location', GeoJsonDict([('type', 'Point'), ('coordinates', [0.550660257722784, 50.851541821108924])])), ('latitude', 50.851541821108924), ('longitude', 0.5506602577227836), ('locationAccuracy', 0.0), ('user', 1), ('statement', 1)]))])])])
Internal Server Error: /statements/api/heatmap/1
Traceback (most recent call last):
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\views\generic\base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\views.py", line 507, in dispatch
    self.response = self.finalize_response(request, response, *args, **kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\views.py", line 419, in finalize_response
    assert isinstance(response, HttpResponseBase), (
AssertionError: Expected a `Response`, `HttpResponse` or `HttpStreamingResponse` to be returned from the view, but received a `<class 'statements.models.Response'>`
[15/Apr/2020 21:55:04] "GET /statements/api/heatmap/1 HTTP/1.1" 500 89414

Solution

Serializer is waiting for data from you. I got the same error when I tried your view with a simple modeling. I think there is something wrong with the definition. can you try the presentation:

def get(self, request):
    final = Response.objects.all()
    serializer = ResponseHeatmapSerializer(data=final, many=True)
    serializer.is_valid(raise_exception=True)
    serializer.save()
    return Response(serializer.data, status=status.HTTP_201_CREATED)

EDITED:

Please excuse me because of my sleeplessness.

The BIG problem here is the name of the table: Response. You have to change the name; somehow it conflicts with the 'Response' that the RestAPI uses.

Change Response(model.Model)'s name to different name.
python manage.py makemigrations
python manage.py migrate

and the view is ready to run (I changed the model name to 'Strawberry':

class ResponseHeatmapList(APIView):
    def get(self, request):
        final = Strawberry.objects.all()
        serializer = ResponseHeatmapSerializer(final, many=True)
        return Response(serializer.data)


class ResponseHeatmapDetail(APIView):
    def get_object(self, pk):
        try:
            return Strawberry.objects.get(pk=pk)
        except Strawberry.DoesNotExist:
            raise Http404

    def get(self, request, pk, format=None):
        final = self.get_object(pk)
        serializer = ResponseHeatmapSerializer(final)
        return Response(serializer.data)