Fixed #16281 -- Fixed ContentType.get_object_for_this_type() in a multiple database setup.

django/contrib/contenttypes/fields.py

@@ -280,7 +280,9 @@ class GenericForeignKey(FieldCacheMixin):
         if ct_id is not None:
             ct = self.get_content_type(id=ct_id, using=instance._state.db)
             try:
-                rel_obj = ct.get_object_for_this_type(pk=pk_val)
+                rel_obj = ct.get_object_for_this_type(
+                    using=instance._state.db, pk=pk_val
+                )
             except ObjectDoesNotExist:
                 pass
         self.set_cached_value(instance, rel_obj)

django/contrib/contenttypes/models.py

@@ -174,20 +174,20 @@ class ContentType(models.Model):
         except LookupError:
             return None
 
-    def get_object_for_this_type(self, **kwargs):
+    def get_object_for_this_type(self, using=None, **kwargs):
         """
         Return an object of this type for the keyword arguments given.
         Basically, this is a proxy around this object_type's get_object() model
         method. The ObjectNotExist exception, if thrown, will not be caught,
         so code that calls this method should catch it.
         """
-        return self.model_class()._base_manager.using(self._state.db).get(**kwargs)
+        return self.model_class()._base_manager.using(using).get(**kwargs)
 
     def get_all_objects_for_this_type(self, **kwargs):
         """
         Return all objects of this type for the keyword arguments given.
         """
-        return self.model_class()._base_manager.using(self._state.db).filter(**kwargs)
+        return self.model_class()._base_manager.filter(**kwargs)
 
     def natural_key(self):
         return (self.app_label, self.model)

docs/ref/contrib/contenttypes.txt

@@ -106,13 +106,18 @@ methods that allow you to get from a
 :class:`~django.contrib.contenttypes.models.ContentType` instance to the
 model it represents, or to retrieve objects from that model:
 
-.. method:: ContentType.get_object_for_this_type(**kwargs)
+.. method:: ContentType.get_object_for_this_type(using=None, **kwargs)
 
     Takes a set of valid :ref:`lookup arguments <field-lookups-intro>` for the
     model the :class:`~django.contrib.contenttypes.models.ContentType`
     represents, and does
     :meth:`a get() lookup <django.db.models.query.QuerySet.get>`
-    on that model, returning the corresponding object.
+    on that model, returning the corresponding object. The ``using`` argument
+    can be used to specify a different database than the default one.
+
+    .. versionchanged:: 5.1
+
+        The ``using`` argument was added.
 
 .. method:: ContentType.model_class()
 

tests/admin_views/models.py

@@ -83,6 +83,9 @@ class Book(models.Model):
     def __str__(self):
         return self.name
 
+    def get_absolute_url(self):
+        return f"/books/{self.id}/"
+
 
 class Promo(models.Model):
     name = models.CharField(max_length=100, verbose_name="¿Name?")

tests/admin_views/test_multidb.py

@@ -2,6 +2,8 @@ from unittest import mock
 
 from django.contrib import admin
 from django.contrib.auth.models import User
+from django.contrib.contenttypes.models import ContentType
+from django.http import HttpResponse
 from django.test import TestCase, override_settings
 from django.urls import path, reverse
 
@@ -23,8 +25,15 @@ class Router:
 site = admin.AdminSite(name="test_adminsite")
 site.register(Book)
 
+
+def book(request, book_id):
+    b = Book.objects.get(id=book_id)
+    return HttpResponse(b.title)
+
+
 urlpatterns = [
     path("admin/", site.urls),
+    path("books/<book_id>/", book),
 ]
 
 
@@ -88,3 +97,47 @@ class MultiDatabaseTests(TestCase):
                     {"post": "yes"},
                 )
                 mock.atomic.assert_called_with(using=db)
+
+
+class ViewOnSiteRouter:
+    def db_for_read(self, model, instance=None, **hints):
+        if model._meta.app_label in {"auth", "sessions", "contenttypes"}:
+            return "default"
+        return "other"
+
+    def db_for_write(self, model, **hints):
+        if model._meta.app_label in {"auth", "sessions", "contenttypes"}:
+            return "default"
+        return "other"
+
+    def allow_relation(self, obj1, obj2, **hints):
+        return obj1._state.db in {"default", "other"} and obj2._state.db in {
+            "default",
+            "other",
+        }
+
+    def allow_migrate(self, db, app_label, **hints):
+        return True
+
+
+@override_settings(ROOT_URLCONF=__name__, DATABASE_ROUTERS=[ViewOnSiteRouter()])
+class ViewOnSiteTests(TestCase):
+    databases = {"default", "other"}
+
+    def test_contenttype_in_separate_db(self):
+        ContentType.objects.using("other").all().delete()
+        book = Book.objects.using("other").create(name="other book")
+        user = User.objects.create_superuser(
+            username="super", password="secret", email="super@example.com"
+        )
+
+        book_type = ContentType.objects.get(app_label="admin_views", model="book")
+
+        self.client.force_login(user)
+
+        shortcut_url = reverse("admin:view_on_site", args=(book_type.pk, book.id))
+        response = self.client.get(shortcut_url, follow=False)
+        self.assertEqual(response.status_code, 302)
+        self.assertRegex(
+            response.url, f"http://(testserver|example.com)/books/{book.id}/"
+        )

tests/multiple_database/tests.py

@@ -1302,6 +1302,34 @@ class QueryTestCase(TestCase):
             title="Dive into Water", published=datetime.date(2009, 5, 4), extra_arg=True
         )
 
+    @override_settings(DATABASE_ROUTERS=["multiple_database.tests.TestRouter"])
+    def test_contenttype_in_separate_db(self):
+        ContentType.objects.using("other").all().delete()
+        book_other = Book.objects.using("other").create(
+            title="Test title other", published=datetime.date(2009, 5, 4)
+        )
+        book_default = Book.objects.using("default").create(
+            title="Test title default", published=datetime.date(2009, 5, 4)
+        )
+        book_type = ContentType.objects.using("default").get(
+            app_label="multiple_database", model="book"
+        )
+
+        book = book_type.get_object_for_this_type(title=book_other.title)
+        self.assertEqual(book, book_other)
+        book = book_type.get_object_for_this_type(using="other", title=book_other.title)
+        self.assertEqual(book, book_other)
+
+        with self.assertRaises(Book.DoesNotExist):
+            book_type.get_object_for_this_type(title=book_default.title)
+        book = book_type.get_object_for_this_type(
+            using="default", title=book_default.title
+        )
+        self.assertEqual(book, book_default)
+
+        all_books = book_type.get_all_objects_for_this_type()
+        self.assertCountEqual(all_books, [book_other])
+
 
 class ConnectionRouterTestCase(SimpleTestCase):
     @override_settings(