I would like to filter against query params in my REST API - [see django docs on this](http://www.django-rest-framework.org/api-guide/filtering#filtering-against-query-parameters).
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](http://django-filter.readthedocs.org/en/latest/usage.html)

```
    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.