Filtering on a related model that contains a generic foreign key leads to an uncaught error.

[simone6021]

Hello,
first let me thank you for sharing this useful code!

What i found is that if you try to filter by a field that point to a related model which has defined a generic foreign key followinf error is returned:
AttributeError at /api/v1/projects/a/ 'GenericForeignKey' object has no attribute 'formfield'

I tried with ForeignKey and ManyToMany on django 1.9.7 and url_filter from github master branch.

You can test it with the following two models:

from django.db import models
from django.contrib.contenttypes.fields import ContentType
from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation


class A(models.Model):
    name = models.CharField(max_length=256, blank=False, null=False)


class B(models.Model):
    name = models.CharField(max_length=256, blank=False, null=False)
    a = models.ForeignKey('A',
                          models.DO_NOTHING,
                          blank=True,
                          null=True,
                          related_name='b_rel')
    content_type = models.ForeignKey(ContentType, models.DO_NOTHING)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

If you try to filter the model 'A' list by the 'b_rel' field the error appears.

Since i actually tried filtering trough djangorestframework 3.3.3 (even if i think that thi issue is generic), i will leave here the relevant code to publish model 'A' to a rest API so you can test it easily.
Just create an 'A' record and paste the following url after you authenticated (trough the django rest framework browsable api or standard django admin):
http://localhost:8000/api/your-app-name/a/?b_rel=1

views.py

from .serializers import *
from projects.models import A, B
from rest_framework.viewsets import ModelViewSet


class ASerializer(serializers.ModelSerializer):
    class Meta:
        model = A
        fields = [
            'name',
            'b_rel',
        ]


class AViewSet(ModelViewSet):
    serializer_class = ASerializer
    queryset = A.objects.all()
    filter_backends = [DjangoFilterBackend]
    filter_fields = [
        'name',
        'b_rel',
    ]

urls.py

from django.conf.urls import include, url
from rest_framework import routers
from projects.views import AViewSet

router = routers.DefaultRouter()

router.register(r'a', AViewSet, 'projects-a')

urlpatterns = [
    url(r'^api/your-app-name/', include(router.urls)),
]

Since the error occurs when filters for the related model ('B') are built automatically, imho the solution is to check wheter a field actually has a formfield or at least exclude the 'GenericForeignKey' field from filters because they do not have a form field by default, see relevant django documentation..

If you prefer a pull request, just tell me.

[miki725]

@simone6021 sorry for late response.

should be fixed in #25 and will be released in 0.3.

thanks for the report

[simone6021]

Thanks a lot and keep on this good work!