Support multiple databases in inheritance accessors

Co-authored-by: ekaplan1 <eytan.kaplan@nasa.gov>
Co-authored-by: bckohan <bckohan@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 v4.3.0 (202X-XX-XX)
 -------------------
 
+* Fixed `"multi-database support in inheritance accessors. <https://github.com/jazzband/django-polymorphic/pull/550>`_
 * Fixed `Caching in inheritance accessor functions <https://github.com/jazzband/django-polymorphic/pull/510>`_
 * Fixed `Foreign key resolves to parent class when using abstract models <https://github.com/jazzband/django-polymorphic/issues/437>`_
 * Fixed `Support Q expressions that contain subquery expressions <https://github.com/jazzband/django-polymorphic/pull/572>`_

src/polymorphic/models.py

@@ -207,7 +207,7 @@ class PolymorphicModel(models.Model, metaclass=PolymorphicModelBase):
                     rel_obj = field.get_cached_value(self)
                 except KeyError:
                     objects = getattr(model, "_base_objects", model.objects)
-                    rel_obj = objects.get(pk=self.pk)
+                    rel_obj = objects.using(self._state.db or DEFAULT_DB_ALIAS).get(pk=self.pk)
                     field.set_cached_value(self, rel_obj)
                 return rel_obj
 

src/polymorphic/tests/test_multidb.py

@@ -14,6 +14,9 @@ from polymorphic.tests.models import (
     ModelY,
     One2OneRelatingModel,
     RelatingModel,
+    RelationA,
+    RelationB,
+    RelationBase,
 )
 
 
@@ -118,3 +121,19 @@ class MultipleDatabasesTests(TestCase):
 
         # Ensure no queries are made using the default database.
         self.assertNumQueries(0, func)
+
+    def test_deletion_cascade_on_non_default_db(self):
+        def run():
+            base_db1 = RelationA.objects.db_manager("secondary").create(field_a="Base DB1")
+            base_db2 = RelationB.objects.db_manager("secondary").create(
+                field_b="Base DB2", fk=base_db1
+            )
+
+            ContentType.objects.clear_cache()
+
+            RelationBase.objects.db_manager("secondary").filter(pk=base_db2.pk).delete()
+
+            self.assertEqual(RelationB.objects.db_manager("secondary").count(), 0)
+
+        # Ensure no queries are made using the default database.
+        self.assertNumQueries(0, run)