Fixed #22994 -- regression with generic FK + admin list_view

The reason for the regression was that the GenericForeignKey field isn't
something meta.get_field_by_name() should return. The reason is that a
couple of places in Django expects get_field_by_name() to work this way.
It could make sense to return GFKs from get_field_by_name(), but that
should likely be done as part of meta refactoring or virtual fields
refactoring patches.

Thanks to glicerinu@gmail.com for the report and to Tim for working on
the issue.

django/db/models/options.py

@@ -441,7 +441,9 @@ class Options(object):
         for f, model in self.get_fields_with_model():
             cache[f.name] = cache[f.attname] = (f, model, True, False)
         for f in self.virtual_fields:
-            cache[f.name] = (f, None if f.model == self.model else f.model, True, False)
+            if hasattr(f, 'related'):
+                cache[f.name] = cache[f.attname] = (
+                    f, None if f.model == self.model else f.model, True, False)
         if apps.ready:
             self._name_map = cache
         return cache

tests/admin_views/admin.py

@@ -35,7 +35,7 @@ from .models import (Article, Chapter, Child, Parent, Picture, Widget,
     UnchangeableObject, UserMessenger, Simple, Choice, ShortMessage, Telegram,
     FilteredManager, EmptyModelHidden, EmptyModelVisible, EmptyModelMixin,
     State, City, Restaurant, Worker, ParentWithDependentChildren,
-    DependentChild, StumpJoke, FieldOverridePost)
+    DependentChild, StumpJoke, FieldOverridePost, FunkyTag)
 
 
 def callable_year(dt_value):
@@ -827,6 +827,10 @@ class RestaurantAdmin(admin.ModelAdmin):
         return {'name': 'overridden_value'}
 
 
+class FunkyTagAdmin(admin.ModelAdmin):
+    list_display = ('name', 'content_object')
+
+
 site = admin.AdminSite(name="admin")
 site.register(Article, ArticleAdmin)
 site.register(CustomArticle, CustomArticleAdmin)
@@ -882,6 +886,7 @@ site.register(State, StateAdmin)
 site.register(City, CityAdmin)
 site.register(Restaurant, RestaurantAdmin)
 site.register(Worker, WorkerAdmin)
+site.register(FunkyTag, FunkyTagAdmin)
 
 # We intentionally register Promo and ChapterXtra1 but not Chapter nor ChapterXtra2.
 # That way we cover all four cases:

tests/admin_views/tests.py

@@ -1718,11 +1718,26 @@ class AdminViewDeletedObjectsTest(TestCase):
         """
         plot = Plot.objects.get(pk=3)
         FunkyTag.objects.create(content_object=plot, name='hott')
-        should_contain = """<li>Funky tag: hott"""
+        should_contain = """<li>Funky tag: <a href="/test_admin/admin/admin_views/funkytag/1/">hott"""
         response = self.client.get('/test_admin/admin/admin_views/plot/%s/delete/' % quote(3))
         self.assertContains(response, should_contain)
 
 
+@override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',),
+    ROOT_URLCONF="admin_views.urls")
+class TestGenericRelations(TestCase):
+    fixtures = ['admin-views-users.xml', 'deleted-objects.xml']
+
+    def setUp(self):
+        self.client.login(username='super', password='secret')
+
+    def test_generic_content_object_in_list_display(self):
+        plot = Plot.objects.get(pk=3)
+        FunkyTag.objects.create(content_object=plot, name='hott')
+        response = self.client.get('/test_admin/admin/admin_views/funkytag/')
+        self.assertContains(response, "%s</td>" % plot)
+
+
 @override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',),
     ROOT_URLCONF="admin_views.urls")
 class AdminViewStringPrimaryKeyTest(TestCase):

tests/model_meta/test.py

@@ -1,7 +1,7 @@
 from django import test
 
-from django.db.models.fields import related, CharField, Field
-from django.contrib.contenttypes.fields import GenericForeignKey
+from django.db.models.fields import related, CharField, Field, FieldDoesNotExist
+from django.contrib.contenttypes.fields import GenericRelation
 
 from .models import (
     AbstractPerson, BasePerson, Person, Relating, Relation
@@ -650,7 +650,12 @@ class GetFieldByNameTests(OptionsBaseTests):
         self.assertEqual(field_info[1:], (None, False, True))
         self.assertIsInstance(field_info[0], related.RelatedObject)
 
-    def test_get_virtual_field(self):
-        field_info = Person._meta.get_field_by_name('content_object_base')
+    def test_get_generic_foreign_key(self):
+        # For historic reasons generic foreign keys aren't available.
+        with self.assertRaises(FieldDoesNotExist):
+            Person._meta.get_field_by_name('content_object_base')
+
+    def test_get_generic_relation(self):
+        field_info = Person._meta.get_field_by_name('generic_relation_base')
         self.assertEqual(field_info[1:], (None, True, False))
-        self.assertIsInstance(field_info[0], GenericForeignKey)
+        self.assertIsInstance(field_info[0], GenericRelation)