Ticket #7778: model_subclass_deletion.diff

django/db/models/query.py

@@ -834 +834 @@
         update_query = sql.UpdateQuery(cls, connection)
         for field in cls._meta.fields:
             if field.rel and field.null and field.rel.to in seen_objs:
-                update_query.clear_related(field, pk_list)
+                # Only clear a related field if the field's column really exists in the related class.
+                if filter(lambda r_field:r_field.column == field.column, field.rel.to._meta.fields):
+                    update_query.clear_related(field, pk_list)
 
     # Now delete the actual data.
     for cls in ordered_classes: