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

1 files changed, 38 insertions, 2 deletions

diff --git a/django/contrib/contenttypes/fields.py b/django/contrib/contenttypes/fields.py
index f40c2c713c..0242c148fa 100644
--- a/django/contrib/contenttypes/fields.py
+++ b/django/contrib/contenttypes/fields.py
@@ -359,10 +359,46 @@ 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
-        target = opts.pk
-        return [PathInfo(self.model._meta, opts, (target,), self.remote_field, True, False)]
+        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)]
 
     def get_reverse_path_info(self):
         opts = self.model._meta