Merge pull request #5117 from rpkilby/fix-filter-backend

Fix DjangoFilterBackend mro

requirements/requirements-optionals.txt

 # Optional packages which may be used with REST framework.
 markdown==2.6.4
 django-guardian==1.4.8
-django-filter==1.0.0
+django-filter==1.0.2
 coreapi==2.2.4
 coreschema==0.0.4

rest_framework/filters.py

@@ -50,12 +50,17 @@ if django_filters:
                 DeprecationWarning
             )
             return super(FilterSet, self).__init__(*args, **kwargs)
+
+    DFBase = django_filters.rest_framework.DjangoFilterBackend
+
 else:
     def FilterSet():
         assert False, 'django-filter must be installed to use the `FilterSet` class'
 
+    DFBase = BaseFilterBackend
 
-class DjangoFilterBackend(BaseFilterBackend):
+
+class DjangoFilterBackend(DFBase):
     """
     A filter backend that uses django-filter.
     """
@@ -69,9 +74,7 @@ class DjangoFilterBackend(BaseFilterBackend):
             DeprecationWarning
         )
 
-        from django_filters.rest_framework import DjangoFilterBackend
-
-        return DjangoFilterBackend(*args, **kwargs)
+        return super(DjangoFilterBackend, cls).__new__(cls, *args, **kwargs)
 
 
 class SearchFilter(BaseFilterBackend):

tests/test_filters.py

@@ -202,6 +202,21 @@ class IntegrationTestFiltering(CommonFilteringTestCase):
         assert len(w) == 0
 
     @unittest.skipUnless(django_filters, 'django-filter not installed')
+    def test_backend_mro(self):
+        class CustomBackend(filters.DjangoFilterBackend):
+            def filter_queryset(self, request, queryset, view):
+                assert False, "custom filter_queryset should run"
+
+        class DFFilterFieldsRootView(FilterFieldsRootView):
+            filter_backends = (CustomBackend,)
+
+        view = DFFilterFieldsRootView.as_view()
+        request = factory.get('/')
+
+        with pytest.raises(AssertionError, message="custom filter_queryset should run"):
+            view(request).render()
+
+    @unittest.skipUnless(django_filters, 'django-filter not installed')
     def test_get_filtered_fields_root_view(self):
         """
         GET requests to paginated ListCreateAPIView should return paginated results.