Fixed #17918 - Handle proxy models correctly when sorting deletions for databases without deferred constraints. Thanks Nate Bragg for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17756 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/delete_regress/tests.py

@@ -8,7 +8,7 @@ from django.test import TestCase, TransactionTestCase, skipUnlessDBFeature
 
 from .models import (Book, Award, AwardNote, Person, Child, Toy, PlayedWith,
     PlayedWithNote, Email, Researcher, Food, Eaten, Policy, Version, Location,
-    Item, Image, File, Photo, FooFile, FooImage, FooPhoto)
+    Item, Image, File, Photo, FooFile, FooImage, FooPhoto, FooFileProxy)
 
 
 # Can't run this test under SQLite, because you can't
@@ -237,3 +237,24 @@ class ProxyDeleteTest(TestCase):
         # to it.
         self.assertEqual(len(FooFile.objects.all()), 0)
         self.assertEqual(len(FooImage.objects.all()), 0)
+
+
+    def test_delete_proxy_pair(self):
+        """
+        If a pair of proxy models are linked by an FK from one concrete parent
+        to the other, deleting one proxy model cascade-deletes the other, and
+        the deletion happens in the right order (not triggering an
+        IntegrityError on databases unable to defer integrity checks).
+
+        Refs #17918.
+
+        """
+        # Create an Image (proxy of File) and FooFileProxy (proxy of FooFile,
+        # which has an FK to File)
+        image = Image.objects.create()
+        as_file = File.objects.get(pk=image.pk)
+        FooFileProxy.objects.create(my_file=as_file)
+
+        Image.objects.all().delete()
+
+        self.assertEqual(len(FooFileProxy.objects.all()), 0)