Ticket #19652: 0001-Fixed-19652-Fixed-a-regression-introduced-by-9d6d0de.patch

django/db/models/fields/related.py

@@ -498 +498 @@
                     db = self._db or router.db_for_read(self.model, instance=self.instance)
                     qs = super(RelatedManager, self).get_query_set().using(db).filter(**self.core_filters)
                     if getattr(self.instance, attname) is None:
-                        return qs.none()
+                        # We can return qs.none() here, see #19652
+                        return qs.filter(pk__in=[])
                     qs._known_related_objects = {rel_field: {self.instance.pk: self.instance}}
                     return qs
 

tests/modeltests/custom_managers/models.py

@@ -63 +63 @@
 
     def __str__(self):
         return self.name
+
+
+# Bug #19652
+class ObjectQuerySet(models.query.QuerySet):
+    pass
+
+class ObjectManager(models.Manager):
+    use_for_related_fields = True
+
+    def get_query_set(self):
+        return ObjectQuerySet(self.model, using=self._db)
+
+
+class RelatedObject(models.Model):
+    pass
+
+
+class Object(models.Model):
+    related = models.ForeignKey(RelatedObject, related_name='objs')
+
+    objects = ObjectManager()

tests/modeltests/custom_managers/tests.py

@@ -3 +3 @@
 from django.test import TestCase
 from django.utils import six
 
-from .models import Person, Book, Car, PersonManager, PublishedBookManager
+from .models import ObjectQuerySet, RelatedObject, Person, Book, Car, PersonManager, PublishedBookManager
 
 
 class CustomManagerTests(TestCase):
@@ -72 +72 @@
             ],
             lambda c: c.name
         )
+
+    def test_related_manager(self):
+        """
+        Make sure un-saved objects related managers always return an instance
+        of the same class the manager's `get_query_set` returns. Refs #19652.
+        """
+        self.assertIsInstance(RelatedObject().objs.all(), ObjectQuerySet)