From 75dfa92a05c7161edd0ba7bc9ceab9b54d3383db Mon Sep 17 00:00:00 2001
From: Simon Charette <charette.s@gmail.com>
Date: Thu, 1 Nov 2018 01:10:29 -0400
Subject: Fixed #29908 -- Fixed setting of foreign key after related set access
 if ForeignKey uses to_field.

Adjusted known related objects handling of target fields which relies on
from and to_fields and has the side effect of fixing a bug bug causing
N+1 queries when using reverse foreign objects.

Thanks Carsten Fuchs for the report.
---
 tests/foreign_object/tests.py | 17 +++++++++--------
 tests/many_to_one/models.py   |  2 +-
 tests/many_to_one/tests.py    |  7 +++++++
 3 files changed, 17 insertions(+), 9 deletions(-)

(limited to 'tests')

diff --git a/tests/foreign_object/tests.py b/tests/foreign_object/tests.py
index 59d4357802..6af6def6d7 100644
--- a/tests/foreign_object/tests.py
+++ b/tests/foreign_object/tests.py
@@ -69,12 +69,10 @@ class MultiColumnFKTests(TestCase):
             membership_country_id=self.soviet_union.id, person_id=self.bob.id,
             group_id=self.republican.id)
 
-        self.assertQuerysetEqual(
-            self.bob.membership_set.all(), [
-                self.cia.id
-            ],
-            attrgetter("group_id")
-        )
+        with self.assertNumQueries(1):
+            membership = self.bob.membership_set.get()
+            self.assertEqual(membership.group_id, self.cia.id)
+            self.assertIs(membership.person, self.bob)
 
     def test_query_filters_correctly(self):
 
@@ -198,8 +196,11 @@ class MultiColumnFKTests(TestCase):
                 list(p.membership_set.all())
                 for p in Person.objects.prefetch_related('membership_set').order_by('pk')]
 
-        normal_membership_sets = [list(p.membership_set.all())
-                                  for p in Person.objects.order_by('pk')]
+        with self.assertNumQueries(7):
+            normal_membership_sets = [
+                list(p.membership_set.all())
+                for p in Person.objects.order_by('pk')
+            ]
         self.assertEqual(membership_sets, normal_membership_sets)
 
     def test_m2m_through_forward_returns_valid_members(self):
diff --git a/tests/many_to_one/models.py b/tests/many_to_one/models.py
index 2f98bebdc0..ef784cfbe2 100644
--- a/tests/many_to_one/models.py
+++ b/tests/many_to_one/models.py
@@ -71,7 +71,7 @@ class Child(models.Model):
 
 
 class ToFieldChild(models.Model):
-    parent = models.ForeignKey(Parent, models.CASCADE, to_field='name')
+    parent = models.ForeignKey(Parent, models.CASCADE, to_field='name', related_name='to_field_children')
 
 
 # Multiple paths to the same model (#7110, #7125)
diff --git a/tests/many_to_one/tests.py b/tests/many_to_one/tests.py
index b04e6ad77a..28430256dc 100644
--- a/tests/many_to_one/tests.py
+++ b/tests/many_to_one/tests.py
@@ -672,3 +672,10 @@ class ManyToOneTests(TestCase):
         child = ToFieldChild.objects.create(parent=parent)
         with self.assertNumQueries(0):
             self.assertIs(child.parent, parent)
+
+    def test_reverse_foreign_key_instance_to_field_caching(self):
+        parent = Parent.objects.create(name='a')
+        ToFieldChild.objects.create(parent=parent)
+        child = parent.to_field_children.get()
+        with self.assertNumQueries(0):
+            self.assertIs(child.parent, parent)
-- 
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