Using custom methods in filter with django-rest-framework

Question

I would like to filter against query params in my REST API - see django docs on this. However, one parameter I wish to filter by is only available via a model @property

example models.py:

class Listing(models.Model):
    product = models.OneToOneField(Product, related_name='listing')
    ...
    @property
    def category(self):
        return self.product.assets[0].category.name

Here is the setup for my Listing API in accordance with django-filter docs

    class ListingFilter(django_filters.FilterSet):
        product = django_filters.CharFilter(name='product__name')
        category = django_filters.CharFilter(name='category') #DOES NOT WORK!!

        class Meta:
            model = Listing
            fields = ['product','category']

    class ListingList(generics.ListCreateAPIView):
        queryset = Listing.objects.all()
        serializer_class = ListingSerializer
        filter_class = ListingFilter

How can I appropriately filter by listing.category? It is not available on the listing model directly.

Answer 1

Use the 'action' parameter to specify a custom method - see django-filter docs

First define a method that filters a queryset using the value of the category parameter:

    def filter_category(queryset, value):
        if not value:
            return queryset

        queryset = ...custom filtering on queryset using 'value'...
        return queryset

Listing filter should look like this:

    class ListingFilter(django_filters.FilterSet):
        ...
        category = django_filters.CharFilter(action=filter_category)
        ...