prefetch_related does not work for SerializerMethodField in django REST framework serializer

Question

I have a serializer that has a nested serializer field. I had set up eager loading and everything was working great.

However, I had do add some custom filtering to the nested field, which required a SerializerMethodField.

After that change, the prefetch_related eager loading is no longer working. How can I optimize a serializer with SerializerMethodField?

Here was my initial, working setup:

# views.py
class MyView(generics.ListAPIView):
    serializer_class = WorkingSerializer

    def get_queryset(self):
        queryset = MyModel.objects.all()
        queryset = self.get_serializer_class().setup_eager_loading(queryset)
        return queryset

# serializers.py
class WorkingSerializer(serializers.ModelSerializer):
    related_field_name = CustomSerializer(many=True)

    @staticmethod
    def setup_eager_loading(queryset):
        queryset = queryset.prefetch_related('related_field_name')
        return queryset

And here is my changed serializer that doesn't work:

# serializers.py
class NotWorkingSerializer(serializers.ModelSerializer):
    related_field_name = serializers.SerializerMethodField('get_related_field')

    def get_related_field(self, instance):
        queryset = instance.related_field_name.all()
        # some filtering done here
        return queryset

    @staticmethod
    def setup_eager_loading(queryset):
        queryset = queryset.prefetch_related('related_field_name')
        return queryset

Answer 1

Instead of doing the prefetch request in the serializer, you can do that in your actual queryset coming from the View. You can override get_queryset method with the custom query. Not sure what is your actual query but for an example you can do something like:

def get_queryset(self):
    queryset = Model.objects.preftech_related("related_field")
    return queryset

and this queryset will already have your related field in it. You won't have to write custom logic in the serializer.