Fixed #12885 -- Fixed queries with GenericRelations to multi-table inheritance child models.

django/contrib/contenttypes/fields.py

@@ -359,8 +359,44 @@ class GenericRelation(ForeignObject):
         self.to_fields = [self.model._meta.pk.name]
         return [(self.remote_field.model._meta.get_field(self.object_id_field_name), self.model._meta.pk)]
 
+    def _get_path_info_with_parent(self):
+        """
+        Return the path that joins the current model through any parent models.
+        The idea is that if you have a GFK defined on a parent model then we
+        need to join the parent model first, then the child model.
+        """
+        # With an inheritance chain ChildTag -> Tag and Tag defines the
+        # GenericForeignKey, and a TaggedItem model has a GenericRelation to
+        # ChildTag, then we need to generate a join from TaggedItem to Tag
+        # (as Tag.object_id == TaggedItem.pk), and another join from Tag to
+        # ChildTag (as that is where the relation is to). Do this by first
+        # generating a join to the parent model, then generating joins to the
+        # child models.
+        path = []
+        opts = self.remote_field.model._meta
+        parent_opts = opts.get_field(self.object_id_field_name).model._meta
+        target = parent_opts.pk
+        path.append(PathInfo(self.model._meta, parent_opts, (target,), self.remote_field, True, False))
+        # Collect joins needed for the parent -> child chain. This is easiest
+        # to do if we collect joins for the child -> parent chain and then
+        # reverse the direction (call to reverse() and use of
+        # field.remote_field.get_path_info()).
+        parent_field_chain = []
+        while parent_opts != opts:
+            field = opts.get_ancestor_link(parent_opts.model)
+            parent_field_chain.append(field)
+            opts = field.remote_field.model._meta
+        parent_field_chain.reverse()
+        for field in parent_field_chain:
+            path.extend(field.remote_field.get_path_info())
+        return path
+
     def get_path_info(self):
         opts = self.remote_field.model._meta
+        object_id_field = opts.get_field(self.object_id_field_name)
+        if object_id_field.model != opts.model:
+            return self._get_path_info_with_parent()
+        else:
             target = opts.pk
             return [PathInfo(self.model._meta, opts, (target,), self.remote_field, True, False)]
 

tests/generic_relations/tests.py

@@ -405,6 +405,13 @@ class GenericRelationsTests(TestCase):
         # GenericRelations to models that use multi-table inheritance work.
         granite = ValuableRock.objects.create(name='granite', hardness=5)
         ValuableTaggedItem.objects.create(content_object=granite, tag="countertop", value=1)
+        self.assertEqual(ValuableRock.objects.filter(tags__value=1).count(), 1)
+        # We're generating a slightly inefficient query for tags__tag - we
+        # first join ValuableRock -> TaggedItem -> ValuableTaggedItem, and then
+        # we fetch tag by joining TaggedItem from ValuableTaggedItem. The last
+        # join isn't necessary, as TaggedItem <-> ValuableTaggedItem is a
+        # one-to-one join.
+        self.assertEqual(ValuableRock.objects.filter(tags__tag="countertop").count(), 1)
         granite.delete()  # deleting the rock should delete the related tag.
         self.assertEqual(ValuableTaggedItem.objects.count(), 0)