Fixed #30493 -- Fixed prefetch_related() for GenericRelation with different content types.

Co-Authored-By: Mariusz Felisiak <felisiak.mariusz@gmail.com>

Thanks Simon Charette for the review.

1 files changed, 20 insertions, 9 deletions

diff --git a/django/contrib/contenttypes/fields.py b/django/contrib/contenttypes/fields.py
index 62284e980e..4015f16c6b 100644
--- a/django/contrib/contenttypes/fields.py
+++ b/django/contrib/contenttypes/fields.py
@@ -1,4 +1,6 @@
 import functools
+import itertools
+import operator
 from collections import defaultdict
 
 from django.contrib.contenttypes.models import ContentType
@@ -566,19 +568,28 @@ def create_generic_related_manager(superclass, rel):
 
             queryset._add_hints(instance=instances[0])
             queryset = queryset.using(queryset._db or self._db)
-
-            query = {
-                '%s__pk' % self.content_type_field_name: self.content_type.id,
-                '%s__in' % self.object_id_field_name: {obj.pk for obj in instances}
-            }
-
+            # Group instances by content types.
+            content_type_queries = (
+                models.Q(**{
+                    '%s__pk' % self.content_type_field_name: content_type_id,
+                    '%s__in' % self.object_id_field_name: {obj.pk for obj in objs}
+                })
+                for content_type_id, objs in itertools.groupby(
+                    sorted(instances, key=lambda obj: self.get_content_type(obj).pk),
+                    lambda obj: self.get_content_type(obj).pk,
+                )
+            )
+            query = functools.reduce(operator.or_, content_type_queries)
             # We (possibly) need to convert object IDs to the type of the
             # instances' PK in order to match up instances:
             object_id_converter = instances[0]._meta.pk.to_python
             return (
-                queryset.filter(**query),
-                lambda relobj: object_id_converter(getattr(relobj, self.object_id_field_name)),
-                lambda obj: obj.pk,
+                queryset.filter(query),
+                lambda relobj: (
+                    object_id_converter(getattr(relobj, self.object_id_field_name)),
+                    relobj.content_type_id
+                ),
+                lambda obj: (obj.pk, self.get_content_type(obj).pk),
                 False,
                 self.prefetch_cache_name,
                 False,