From 12e6f573adbf825c74042f15b70600341220674b Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Mon, 2 Dec 2019 01:16:32 +0100
Subject: [PATCH] Refs #26552 -- Added test for reloading the database with
 self-referential objects.

---
 tests/backends/base/test_creation.py | 24 +++++++++++++++++++++++-
 tests/backends/models.py             |  5 +++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/tests/backends/base/test_creation.py b/tests/backends/base/test_creation.py
index 1d345c611b6..19a39150219 100644
--- a/tests/backends/base/test_creation.py
+++ b/tests/backends/base/test_creation.py
@@ -7,7 +7,7 @@ from django.db.backends.base.creation import (
 )
 from django.test import SimpleTestCase, TransactionTestCase
 
-from ..models import Object, ObjectReference
+from ..models import Object, ObjectReference, ObjectSelfReference
 
 
 def get_connection_copy():
@@ -101,3 +101,25 @@ class TestDeserializeDbFromString(TransactionTestCase):
         obj_ref = ObjectReference.objects.get()
         self.assertEqual(obj.obj_ref, obj_ref)
         self.assertEqual(obj_ref.obj, obj)
+
+    def test_self_reference(self):
+        # serialize_db_to_string() and deserialize_db_from_string() handles
+        # self references.
+        obj_1 = ObjectSelfReference.objects.create(key='X')
+        obj_2 = ObjectSelfReference.objects.create(key='Y', obj=obj_1)
+        obj_1.obj = obj_2
+        obj_1.save()
+        # Serialize objects.
+        with mock.patch('django.db.migrations.loader.MigrationLoader') as loader:
+            # serialize_db_to_string() serializes only migrated apps, so mark
+            # the backends app as migrated.
+            loader_instance = loader.return_value
+            loader_instance.migrated_apps = {'backends'}
+            data = connection.creation.serialize_db_to_string()
+        ObjectSelfReference.objects.all().delete()
+        # Deserialize objects.
+        connection.creation.deserialize_db_from_string(data)
+        obj_1 = ObjectSelfReference.objects.get(key='X')
+        obj_2 = ObjectSelfReference.objects.get(key='Y')
+        self.assertEqual(obj_1.obj, obj_2)
+        self.assertEqual(obj_2.obj, obj_1)
diff --git a/tests/backends/models.py b/tests/backends/models.py
index 277a3a12038..87809b84a8d 100644
--- a/tests/backends/models.py
+++ b/tests/backends/models.py
@@ -102,6 +102,11 @@ class ObjectReference(models.Model):
         return str(self.obj_id)
 
 
+class ObjectSelfReference(models.Model):
+    key = models.CharField(max_length=3, unique=True)
+    obj = models.ForeignKey('ObjectSelfReference', models.SET_NULL, null=True)
+
+
 class RawData(models.Model):
     raw_data = models.BinaryField()