[1.6.x] Fixed #23370 -- defer() + select_related() crashed with inherited models.

Backport of 6613ea6e3f from master

1 files changed, 37 insertions, 0 deletions

diff --git a/tests/model_inheritance/tests.py b/tests/model_inheritance/tests.py
index dc40d2d2e0..f96fe5e4dd 100644
--- a/tests/model_inheritance/tests.py
+++ b/tests/model_inheritance/tests.py
@@ -275,6 +275,43 @@ class ModelInheritanceTests(TestCase):
             lambda: ItalianRestaurant.objects.select_related("chef")[0].chef
         )
 
+    def test_select_related_defer(self):
+        """
+        #23370 - Should be able to defer child fields when using
+        select_related() from parent to child.
+        """
+        Restaurant.objects.create(
+            name="Demon Dogs",
+            address="944 W. Fullerton",
+            serves_hot_dogs=True,
+            serves_pizza=False,
+            rating=2,
+        )
+        ItalianRestaurant.objects.create(
+            name="Ristorante Miron",
+            address="1234 W. Ash",
+            serves_hot_dogs=False,
+            serves_pizza=False,
+            serves_gnocchi=True,
+            rating=4,
+        )
+
+        qs = (Restaurant.objects
+            .select_related("italianrestaurant")
+            .defer("italianrestaurant__serves_gnocchi")
+            .order_by("rating"))
+
+        # Test that the field was actually defered
+        with self.assertNumQueries(2):
+            objs = list(qs.all())
+            self.assertTrue(objs[1].italianrestaurant.serves_gnocchi)
+
+        # Test that model fields where assigned correct values
+        self.assertEqual(qs[0].name, 'Demon Dogs')
+        self.assertEqual(qs[0].rating, 2)
+        self.assertEqual(qs[1].italianrestaurant.name, 'Ristorante Miron')
+        self.assertEqual(qs[1].italianrestaurant.rating, 4)
+
     def test_mixin_init(self):
         m = MixinModel()
         self.assertEqual(m.other_attr, 1)