[1.9.x] Fixed #26286 -- Prevented content type managers from sharing their cache.

This should prevent managers methods from returning content type instances
registered to foreign apps now that these managers are also attached to models
created during migration phases.

Thanks Tim for the review.

Refs #23822.

Backport of 3938b3ccaa85f1c366909a4839696007726a09da from master

1 files changed, 13 insertions, 1 deletions

diff --git a/tests/contenttypes_tests/test_models.py b/tests/contenttypes_tests/test_models.py
index eb436b6a64..75cea0a4d8 100644
--- a/tests/contenttypes_tests/test_models.py
+++ b/tests/contenttypes_tests/test_models.py
@@ -2,7 +2,7 @@ from __future__ import unicode_literals
 
 import warnings
 
-from django.contrib.contenttypes.models import ContentType
+from django.contrib.contenttypes.models import ContentType, ContentTypeManager
 from django.contrib.contenttypes.views import shortcut
 from django.contrib.sites.shortcuts import get_current_site
 from django.db.utils import IntegrityError, OperationalError, ProgrammingError
@@ -170,6 +170,18 @@ class ContentTypesTests(TestCase):
             DeferredProxyModel: proxy_model_ct,
         })
 
+    def test_cache_not_shared_between_managers(self):
+        with self.assertNumQueries(1):
+            ContentType.objects.get_for_model(ContentType)
+        with self.assertNumQueries(0):
+            ContentType.objects.get_for_model(ContentType)
+        other_manager = ContentTypeManager()
+        other_manager.model = ContentType
+        with self.assertNumQueries(1):
+            other_manager.get_for_model(ContentType)
+        with self.assertNumQueries(0):
+            other_manager.get_for_model(ContentType)
+
     @override_settings(ALLOWED_HOSTS=['example.com'])
     def test_shortcut_view(self):
         """