'ListSerializer' when serializing a queryset using Django Rest Framework

Question

I have a slightly complicated APIView which makes that I can't use a generic ListAPIView to return a queryset. But I can't seem to simply serialize a simple Django queryset using a ModelSerializer, even when I set many=True.

Somehow this doesn't work:

serializers.py:

class SomeModelSerializer(serializers.ModelSerializer):

    class Meta:
        model = SomeModel
        fields = ['some_field']

views.py:

from rest_framework.response import Response

class SomeAPIView(APIView):
    serializer_class = SomeInputSerializer

    def post(self, request, format=None):
        serializer = self.serializer_class(data=request.data)
        if serializer.is_valid():
            # first some business logic, then return results
            results = SomeModel.objects.all()
            output_serializer = SomeModelSerializer(results, many=True)
            return Response(output_serializer.data)

All I keep getting is: 'ListSerializer' object is not iterable.

What am I doing wrong?

Error:

/projectfolder/venv/lib/python2.7/site-packages/django/template/defaulttags.py in render
            try:
                values = self.sequence.resolve(context, True)
            except VariableDoesNotExist:
                values = []
            if values is None:
                values = []
            if not hasattr(values, '__len__'):
                values = list(values) ...
            len_values = len(values)
            if len_values < 1:
                return self.nodelist_empty.render(context)
            nodelist = []
            if self.is_reversed:
                values = reversed(values)

values = list(values) seems to be responsible for the error

This code looks fine. Could you provide more of your actual code? Which line throws the error? — ilse2005
– ilse2005, Commented Apr 13, 2016 at 7:13
@ilse2005 The last one. I can actually print output_serializer.data to the console with no problems, but get the error when returning the Response object. I've included an error log. — Vincent van Leeuwen
– Vincent van Leeuwen, Commented Apr 13, 2016 at 9:38

D. Peter · Accepted Answer · 2016-09-14 08:49:46Z

7

Was running into the same problem as you did. I found a quick and simple fix for the error: Copy the serializer data to a new array and return that.

results = SomeModel.objects.all()

output_serializer = SomeModelSerializer(results, many=True)    
data = output_serializer.data[:]

return Response(data)

This works for me, hopefully for you as well.

answered Sep 14, 2016 at 8:49

D. Peter

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Comments

ncole458 · Accepted Answer · 2016-12-15 23:07:37Z

Below works for me using an as_view() url:

 class ListCreateMemberViewSet(generics.ListCreateAPIView):
        """
        API endpoint that allows multiple members to be created.
        """
        queryset = Member.objects.none()
        serializer_class = MemberSerializer

    def get_queryset(self):
         queryset = Member.objects.all()
         return queryset

    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data, many=isinstance(request.data, list))
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        results = Member.objects.all()
        output_serializer = MemberSerializer(results, many=True)
        data = output_serializer.data[:]
        return Response(data)

VARAK · Accepted Answer · 2019-09-25 15:36:35Z

The error is a result of trying to run a list on a serializer directly.

For example, this would raise the above exception:

results = Member.objects.all()
output_serializer = MemberSerializer(results, many=True)
all_results = list(output_serializer) # this line here
all_results += output_serializer  # or this line here

And this would not (difference is that we are listing output_serializer.data instead of output_serializer):

results = Member.objects.all()
output_serializer = MemberSerializer(results, many=True)
all_results = list(output_serializer.data)
all_results += output_serializer.data

I have the feeling that in the original question, the example code was not 100% matching the actual code.

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