Fixed #17485 -- Made defer work with select_related

This commit tackles a couple of issues. First, in certain cases there
were some mixups if field.attname or field.name should be deferred.
Field.attname is now always used.

Another issue tackled is a case where field is both deferred by
.only(), and selected by select_related. This case is now an error.

A lot of thanks to koniiiik (Michal Petrucha) for the patch, and
to Andrei Antoukh for review.

3 files changed, 29 insertions, 3 deletions

diff --git a/tests/regressiontests/defer_regress/models.py b/tests/regressiontests/defer_regress/models.py
index 812d2da206..bd4f845f27 100644
--- a/tests/regressiontests/defer_regress/models.py
+++ b/tests/regressiontests/defer_regress/models.py
@@ -47,3 +47,7 @@ class SimpleItem(models.Model):
 
 class Feature(models.Model):
     item = models.ForeignKey(SimpleItem)
+
+class ItemAndSimpleItem(models.Model):
+    item = models.ForeignKey(Item)
+    simple = models.ForeignKey(SimpleItem)
diff --git a/tests/regressiontests/defer_regress/tests.py b/tests/regressiontests/defer_regress/tests.py
index 1f07d4c9a8..53bb59f5b3 100644
--- a/tests/regressiontests/defer_regress/tests.py
+++ b/tests/regressiontests/defer_regress/tests.py
@@ -9,7 +9,7 @@ from django.db.models.loading import cache
 from django.test import TestCase
 
 from .models import (ResolveThis, Item, RelatedItem, Child, Leaf, Proxy,
-    SimpleItem, Feature)
+    SimpleItem, Feature, ItemAndSimpleItem)
 
 
 class DeferRegressionTest(TestCase):
@@ -109,6 +109,7 @@ class DeferRegressionTest(TestCase):
                 Child,
                 Feature,
                 Item,
+                ItemAndSimpleItem,
                 Leaf,
                 Proxy,
                 RelatedItem,
@@ -125,12 +126,16 @@ class DeferRegressionTest(TestCase):
                 ),
             )
         )
+        # FIXME: This is dependent on the order in which tests are run --
+        # this test case has to be the first, otherwise a LOT more classes
+        # appear.
         self.assertEqual(
             klasses, [
                 "Child",
                 "Child_Deferred_value",
                 "Feature",
                 "Item",
+                "ItemAndSimpleItem",
                 "Item_Deferred_name",
                 "Item_Deferred_name_other_value_text",
                 "Item_Deferred_name_other_value_value",
@@ -139,7 +144,7 @@ class DeferRegressionTest(TestCase):
                 "Leaf",
                 "Leaf_Deferred_child_id_second_child_id_value",
                 "Leaf_Deferred_name_value",
-                "Leaf_Deferred_second_child_value",
+                "Leaf_Deferred_second_child_id_value",
                 "Leaf_Deferred_value",
                 "Proxy",
                 "RelatedItem",
@@ -175,6 +180,23 @@ class DeferRegressionTest(TestCase):
         self.assertEqual(1, qs.count())
         self.assertEqual('Foobar', qs[0].name)
 
+    def test_defer_with_select_related(self):
+        item1 = Item.objects.create(name="first", value=47)
+        item2 = Item.objects.create(name="second", value=42)
+        simple = SimpleItem.objects.create(name="simple", value="23")
+        related = ItemAndSimpleItem.objects.create(item=item1, simple=simple)
+
+        obj = ItemAndSimpleItem.objects.defer('item').select_related('simple').get()
+        self.assertEqual(obj.item, item1)
+        self.assertEqual(obj.item_id, item1.id)
+
+        obj.item = item2
+        obj.save()
+
+        obj = ItemAndSimpleItem.objects.defer('item').select_related('simple').get()
+        self.assertEqual(obj.item, item2)
+        self.assertEqual(obj.item_id, item2.id)
+
     def test_deferred_class_factory(self):
         from django.db.models.query_utils import deferred_class_factory
         new_class = deferred_class_factory(Item,
diff --git a/tests/regressiontests/select_related_regress/tests.py b/tests/regressiontests/select_related_regress/tests.py
index e35157dbaf..73b0a8a875 100644
--- a/tests/regressiontests/select_related_regress/tests.py
+++ b/tests/regressiontests/select_related_regress/tests.py
@@ -133,7 +133,7 @@ class SelectRelatedRegressTests(TestCase):
         self.assertEqual(troy.state.name, 'Western Australia')
 
         # Also works if you use only, rather than defer
-        troy = SpecialClient.objects.select_related('state').only('name').get(name='Troy Buswell')
+        troy = SpecialClient.objects.select_related('state').only('name', 'state').get(name='Troy Buswell')
 
         self.assertEqual(troy.name, 'Troy Buswell')
         self.assertEqual(troy.value, 42)