From f8b8b00f0197e52f7a0986fae51462be174dbaea Mon Sep 17 00:00:00 2001
From: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Date: Thu, 23 May 2019 20:33:37 +0200
Subject: Fixed #30501 -- Preventing QuerySet.reverse() from mutating
 expressions in QuerySet.order_by and Meta.ordering.

---
 tests/ordering/tests.py | 38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

(limited to 'tests/ordering')

diff --git a/tests/ordering/tests.py b/tests/ordering/tests.py
index f0c4bba999..1466d350a1 100644
--- a/tests/ordering/tests.py
+++ b/tests/ordering/tests.py
@@ -210,6 +210,15 @@ class OrderingTests(TestCase):
     def test_reverse_ordering_pure(self):
         qs1 = Article.objects.order_by(F('headline').asc())
         qs2 = qs1.reverse()
+        self.assertQuerysetEqual(
+            qs2, [
+                'Article 4',
+                'Article 3',
+                'Article 2',
+                'Article 1',
+            ],
+            attrgetter('headline'),
+        )
         self.assertQuerysetEqual(
             qs1, [
                 "Article 1",
@@ -219,14 +228,29 @@ class OrderingTests(TestCase):
             ],
             attrgetter("headline")
         )
+
+    def test_reverse_meta_ordering_pure(self):
+        Article.objects.create(
+            headline='Article 5',
+            pub_date=datetime(2005, 7, 30),
+            author=self.author_1,
+            second_author=self.author_2,
+        )
+        Article.objects.create(
+            headline='Article 5',
+            pub_date=datetime(2005, 7, 30),
+            author=self.author_2,
+            second_author=self.author_1,
+        )
         self.assertQuerysetEqual(
-            qs2, [
-                "Article 4",
-                "Article 3",
-                "Article 2",
-                "Article 1",
-            ],
-            attrgetter("headline")
+            Article.objects.filter(headline='Article 5').reverse(),
+            ['Name 2', 'Name 1'],
+            attrgetter('author.name'),
+        )
+        self.assertQuerysetEqual(
+            Article.objects.filter(headline='Article 5'),
+            ['Name 1', 'Name 2'],
+            attrgetter('author.name'),
         )
 
     def test_no_reordering_after_slicing(self):
-- 
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