How do you filter a nested serializer in Django Rest Framework?

Question

In Django Rest Framework, how do you filter a serializer when it's nested in another serializer?

My filters are imposed in the DRF viewsets, but when you call a serializer from inside another serializer, the viewset of the nested serializer never gets called, so the nested results appear unfiltered.

I have tried adding a filter on originating viewset, but it doesn't seem to filter the nested results because the nested results get called as a separate pre-fretched query. (The nested serializer is a reverse lookup, you see.)

Is it possible to add a get_queryset() override in the nested serializer itself (moving it out of the viewset), to add the filter there? I've tried that, too, with no luck.

This is what I tried, but it doesn't even seem to get called:

class QuestionnaireSerializer(serializers.ModelSerializer):
    edition = EditionSerializer(read_only=True)
    company = serializers.StringRelatedField(read_only=True)

    class Meta:
        model = Questionnaire

    def get_queryset(self):
        query = super(QuestionnaireSerializer, self).get_queryset(instance)
        if not self.request.user.is_staff:
            query = query.filter(user=self.request.user, edition__hide=False)
        return query

Answer 1

You can subclass the ListSerializer and overwrite the to_representation method.

By default the to_representation method calls data.all() on the nested queryset. So you effectively need to make data = data.filter(**your_filters) before the method is called. Then you need to add your subclassed ListSerializer as the list_serializer_class on the meta of the nested serializer.

1. subclass ListSerializer, overwriting to_representation and then calling super
2. add subclassed ListSerializer as the meta list_serializer_class on the nested Serializer

Here is the relevant code for your sample.

class FilteredListSerializer(serializers.ListSerializer):

    def to_representation(self, data):
        data = data.filter(user=self.context['request'].user, edition__hide=False)
        return super(FilteredListSerializer, self).to_representation(data)


class EditionSerializer(serializers.ModelSerializer):

    class Meta:
        list_serializer_class = FilteredListSerializer
        model = Edition


class QuestionnaireSerializer(serializers.ModelSerializer):
    edition = EditionSerializer(read_only=True)
    company = serializers.StringRelatedField(read_only=True)

    class Meta:
        model = Questionnaire