From 01a381cc17e6747e1d9e7b95a39e885029fd2a81 Mon Sep 17 00:00:00 2001
From: Hasan Ramezani <hasan.r67@gmail.com>
Date: Wed, 13 May 2020 14:44:10 +0200
Subject: [PATCH] Fixed #31580 -- Added error messages on distinct() following
 union(), intersection(), and difference().

---
 django/db/models/query.py            | 1 +
 tests/queries/test_qs_combinators.py | 1 +
 2 files changed, 2 insertions(+)

diff --git a/django/db/models/query.py b/django/db/models/query.py
index e0eeccefa6..5c70229263 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -1138,6 +1138,7 @@ class QuerySet:
         """
         Return a new QuerySet instance that will select only distinct results.
         """
+        self._not_support_combined_queries('distinct')
         assert not self.query.is_sliced, \
             "Cannot create distinct fields once a slice has been taken."
         obj = self._chain()
diff --git a/tests/queries/test_qs_combinators.py b/tests/queries/test_qs_combinators.py
index 1d159e1fed..d2e7d2b80d 100644
--- a/tests/queries/test_qs_combinators.py
+++ b/tests/queries/test_qs_combinators.py
@@ -272,6 +272,7 @@ class QuerySetSetOperationTests(TestCase):
                 'annotate',
                 'defer',
                 'delete',
+                'distinct',
                 'exclude',
                 'extra',
                 'filter',