Fixed #30493 -- Fixed GenericRelation's prefetch queryset

django/contrib/contenttypes/fields.py

@@ -1,4 +1,6 @@
+import operator
 from collections import defaultdict
+from functools import reduce
 
 from django.contrib.contenttypes.models import ContentType
 from django.core import checks
@@ -523,6 +525,7 @@ def __init__(self, instance=None):
             self.object_id_field_name = rel.field.object_id_field_name
             self.prefetch_cache_name = rel.field.attname
             self.pk_val = instance.pk
+            self.for_concrete_model = rel.field.for_concrete_model
 
             self.core_filters = {
                 '%s__pk' % self.content_type_field_name: content_type.id,
@@ -558,25 +561,34 @@ def get_queryset(self):
                 queryset = super().get_queryset()
                 return self._apply_rel_filters(queryset)
 
+        def get_content_type(self, obj):
+            return ContentType.objects.db_manager(obj._state.db).get_for_model(
+                obj, for_concrete_model=self.for_concrete_model)
+
         def get_prefetch_queryset(self, instances, queryset=None):
             if queryset is None:
                 queryset = super().get_queryset()
 
             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}
-            }
+            or_queries = [models.Q(**{
+                '%s__pk' % self.content_type_field_name: self.get_content_type(instance).pk,
+                '%s' % self.object_id_field_name: instance.pk
+            }) for instance in instances]
+            queryset = queryset.filter(reduce(operator.or_, or_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,
+                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,

tests/generic_relations/tests.py

@@ -546,6 +546,17 @@ def test_add_then_remove_after_prefetch(self):
         platypus.tags.remove(weird_tag)
         self.assertSequenceEqual(platypus.tags.all(), [furry_tag])
 
+    def test_prefetch_related_generic_relation(self):
+        bacon = Vegetable.objects.create(name="Bacon", is_yucky=False)
+        bear = Animal.objects.create(common_name="bear")
+        tag1 = TaggedItem.objects.create(content_object=bacon, tag="bacon")
+        tag2 = TaggedItem.objects.create(content_object=bear, tag="bear")
+        prefetched_queryset = TaggedItem.objects.prefetch_related("content_object", "content_object__tags")
+        with self.assertNumQueries(4):
+            prefetched_items = list(prefetched_queryset)
+        self.assertEqual(list(prefetched_items[0].content_object.tags.all()), [tag1])
+        self.assertEqual(list(prefetched_items[1].content_object.tags.all()), [tag2])
+
 
 class ProxyRelatedModelTest(TestCase):
     def test_default_behavior(self):