Fixed #25685 -- Fixed a duplicate query regression on deletion of proxied models.

Thanks to Trac alias ppetrid for the report and Tim for the review.

Conflicts:
	django/db/models/deletion.py
	tests/delete/tests.py

Forward port of 7c3ef19978 from stable/1.8.x

docs/releases/1.8.7.txt

@@ -39,3 +39,6 @@ Bugfixes
 
 * Fixed ``Model.refresh_from_db()`` updating of ``ForeignKey`` fields with
   ``on_delete=models.SET_NULL`` (:ticket:`25715`).
+
+* Fixed a duplicate query regression in 1.8 on proxied model deletion
+  (:ticket:`25685`).

tests/delete/models.py

@@ -99,6 +99,12 @@ class Avatar(models.Model):
     desc = models.TextField(null=True)
 
 
+# This model is used to test a duplicate query regression (#25685)
+class AvatarProxy(Avatar):
+    class Meta:
+        proxy = True
+
+
 class User(models.Model):
     avatar = models.ForeignKey(Avatar, models.CASCADE, null=True)
 

tests/delete/tests.py

@@ -414,6 +414,17 @@ class DeletionTests(TestCase):
         for k, v in existed_objs.items():
             self.assertEqual(deleted_objs[k], v)
 
+    def test_proxied_model_duplicate_queries(self):
+        """
+        #25685 - Deleting instances of a model with existing proxy
+        classes should not issue multiple queries during cascade
+        deletion of referring models.
+        """
+        avatar = Avatar.objects.create()
+        # One query for the Avatar table and a second for the User one.
+        with self.assertNumQueries(2):
+            avatar.delete()
+
 
 class FastDeleteTests(TestCase):