Fixed #28917 -- Prevented Paginator's unordered warning on EmptyQuerySet.

Thanks carltongibson for the idea and weijunji for the initial patch.

django/db/models/query.py

@@ -1100,8 +1100,10 @@ class QuerySet:
     def ordered(self):
         """
         Return True if the QuerySet is ordered -- i.e. has an order_by()
-        clause or a default ordering on the model.
+        clause or a default ordering on the model (or is empty).
         """
+        if isinstance(self, EmptyQuerySet):
+            return True
         if self.query.extra_order_by or self.query.order_by:
             return True
         elif self.query.default_ordering and self.query.get_meta().ordering:

tests/pagination/tests.py

 import unittest
+import warnings
 from datetime import datetime
 
 from django.core.paginator import (
@@ -368,6 +369,11 @@ class ModelPaginationTests(TestCase):
         # is appropriate).
         self.assertEqual(cm.filename, __file__)
 
+    def test_paginating_empty_queryset_does_not_warn(self):
+        with warnings.catch_warnings(record=True) as recorded:
+            Paginator(Article.objects.none(), 5)
+        self.assertEqual(len(recorded), 0)
+
     def test_paginating_unordered_object_list_raises_warning(self):
         """
         Unordered object list warning with an object that has an orderd

tests/queries/tests.py

@@ -2024,6 +2024,9 @@ class QuerysetOrderedTests(unittest.TestCase):
     def test_explicit_ordering(self):
         self.assertIs(Annotation.objects.all().order_by('id').ordered, True)
 
+    def test_empty_queryset(self):
+        self.assertIs(Annotation.objects.none().ordered, True)
+
     def test_order_by_extra(self):
         self.assertIs(Annotation.objects.all().extra(order_by=['id']).ordered, True)