backport fix for #845

Author: bckohan

docs/changelog.rst

@@ -1,6 +1,11 @@
 Changelog
 =========
 
+v4.9.1 (2026-01-15)
+-------------------
+
+* Fixed `Meta.base_manager_name is not respected <https://github.com/jazzband/django-polymorphic/issues/845>`_
+
 v4.9.0 (2026-01-09)
 -------------------
 

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "django-polymorphic"
-version = "4.9.0"
+version = "4.9.1"
 description = "Seamless polymorphic inheritance for Django models."
 readme = "README.md"
 license = "BSD-3-Clause"

src/polymorphic/__init__.py

@@ -19,7 +19,7 @@
 Seamless Polymorphic Inheritance for Django Models
 """
 
-VERSION = "4.9.0"
+VERSION = "4.9.1"
 
 __title__ = "Django Polymorphic"
 __version__ = VERSION  # version synonym for backwards compatibility

src/polymorphic/base.py

@@ -71,28 +71,28 @@ class PolymorphicModelBase(ModelBase):
     """
 
     def __new__(cls, model_name, bases, attrs, **kwargs):
-        # create new model
-        new_class = super().__new__(cls, model_name, bases, attrs, **kwargs)
+        # skip special setup for PolymorphicModel itself
+        if attrs.pop("_meta_skip", False):
+            return super().__new__(cls, model_name, bases, attrs, **kwargs)
 
-        if new_class._meta.base_manager_name is None:
-            # by default, use polymorphic manager as the base manager
-            new_class._meta.base_manager_name = new_class._meta.default_manager_name or "objects"
+        from .models import PolymorphicModel
 
-        # ensure base_manager is a plain PolymorphicManager by resetting it if it
-        # was not explicitly set and it defaults to a changed default_manager
-        # the base class manager determination logic is complex enough that we prefer
-        # to observe its application and correct rather than preempting it
-        if (
-            type(new_class._meta.default_manager) is not PolymorphicManager
-            and new_class._meta.base_manager is new_class._meta.default_manager
+        new_class = super().__new__(cls, model_name, bases, attrs, **kwargs)
+
+        if not any(
+            parent._meta.base_manager_name
+            for parent in new_class.mro()
+            if issubclass(parent, PolymorphicModel)
         ):
-            manager = PolymorphicManager()
-            manager.name = "_base_manager"
-            manager.model = new_class
-            manager.auto_created = True
-            new_class._meta.base_manager_name = None
-            # write new manager to property cache
-            new_class._meta.__dict__["base_manager"] = manager
+            if new_class._meta.default_manager.__class__ is PolymorphicManager:
+                new_class._meta.__dict__["base_manager"] = new_class._meta.default_manager
+            else:
+                manager = PolymorphicManager()
+                manager.name = "_base_manager"
+                manager.model = new_class
+                manager.auto_created = True
+                # write new manager to property cache
+                new_class._meta.__dict__["base_manager"] = manager
 
         # validate resulting default manager
         if not new_class._meta.abstract and not new_class._meta.swapped:

src/polymorphic/models.py

@@ -35,6 +35,8 @@ class PolymorphicModel(models.Model, metaclass=PolymorphicModelBase):
     and provides a polymorphic manager as the default manager (and as 'objects').
     """
 
+    _meta_skip = True
+
     # for PolymorphicModelBase, so it can tell which models are polymorphic and which are not (duck typing)
     polymorphic_model_marker = True
 

src/polymorphic/tests/deletion/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-09 13:25
+# Generated by Django 4.2 on 2026-01-15 16:35
 
 from decimal import Decimal
 from django.conf import settings
@@ -12,8 +12,8 @@ class Migration(migrations.Migration):
     initial = True
 
     dependencies = [
-        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
         ('contenttypes', '0002_remove_content_type_name'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
     ]
 
     operations = [

src/polymorphic/tests/examples/views/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-09 13:25
+# Generated by Django 4.2 on 2026-01-15 16:35
 
 from django.db import migrations, models
 import django.db.models.deletion

src/polymorphic/tests/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-09 13:25
+# Generated by Django 4.2 on 2026-01-15 16:35
 
 from django.conf import settings
 from django.db import migrations, models
@@ -14,8 +14,8 @@ class Migration(migrations.Migration):
     initial = True
 
     dependencies = [
-        ('auth', '0012_alter_user_first_name_max_length'),
         ('contenttypes', '0002_remove_content_type_name'),
+        ('auth', '0012_alter_user_first_name_max_length'),
     ]
 
     operations = [
@@ -233,6 +233,26 @@ class Migration(migrations.Migration):
                 'abstract': False,
             },
         ),
+        migrations.CreateModel(
+            name='ManagerTest',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=30)),
+                ('polymorphic_ctype', models.ForeignKey(editable=False, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='polymorphic_%(app_label)s.%(class)s_set+', to='contenttypes.contenttype')),
+            ],
+            options={
+                'base_manager_name': 'objects',
+            },
+        ),
+        migrations.CreateModel(
+            name='ManagerTestPlain',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+            ],
+            options={
+                'base_manager_name': 'objects',
+            },
+        ),
         migrations.CreateModel(
             name='Model2A',
             fields=[
@@ -670,6 +690,23 @@ class Migration(migrations.Migration):
             },
             bases=('tests.m2mthroughbase',),
         ),
+        migrations.CreateModel(
+            name='ManagerTestChild',
+            fields=[
+                ('managertest_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.managertest')),
+            ],
+            options={
+                'abstract': False,
+            },
+            bases=('tests.managertest',),
+        ),
+        migrations.CreateModel(
+            name='ManagerTestChildPlain',
+            fields=[
+                ('managertestplain_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.managertestplain')),
+            ],
+            bases=('tests.managertestplain',),
+        ),
         migrations.CreateModel(
             name='Middle',
             fields=[
@@ -770,7 +807,6 @@ class Migration(migrations.Migration):
             bases=(polymorphic.showfields.ShowFieldTypeAndContent, 'tests.model2a'),
             managers=[
                 ('my_objects', django.db.models.manager.Manager()),
-                ('objects', django.db.models.manager.Manager()),
             ],
         ),
         migrations.CreateModel(

src/polymorphic/tests/models.py

@@ -1065,3 +1065,30 @@ def natural_key(self):
         return self.foo.natural_key()
 
     natural_key.dependencies = ["tests.natkeyparent"]
+
+
+class ManagerTest(PolymorphicModel):
+    name = models.CharField(max_length=30)
+
+    objects = CustomBaseManager()
+
+    class Meta:
+        base_manager_name = "objects"
+
+
+class ManagerTestChild(ManagerTest):
+    pass
+
+
+class PlainManager(models.Manager): ...
+
+
+class ManagerTestPlain(models.Model):
+    objects = PlainManager()
+
+    class Meta:
+        base_manager_name = "objects"
+
+
+class ManagerTestChildPlain(ManagerTestPlain):
+    pass

src/polymorphic/tests/test_orm.py

@@ -473,7 +473,7 @@ def test_create_instanceof_q(self):
         assert dict(q.children) == dict(polymorphic_ctype__in=expected)
 
     def test_base_manager(self):
-        from .models import CustomBaseManager
+        from .models import ManagerTest, CustomBaseManager, ManagerTestChild
 
         def base_manager(model):
             return (type(model._base_manager), model._base_manager.model)
@@ -503,6 +503,13 @@ def base_manager(model):
         assert type(Model2CNamedManagers._base_manager) is CustomBaseManager
         assert type(Model2CNamedDefault._base_manager) is PolymorphicManager
 
+        assert type(ManagerTest._base_manager) is CustomBaseManager
+        assert type(ManagerTest._default_manager) is CustomBaseManager
+        assert ManagerTest._base_manager is ManagerTest._default_manager
+        assert type(ManagerTestChild._base_manager) is CustomBaseManager
+        assert type(ManagerTestChild._default_manager) is CustomBaseManager
+        assert ManagerTestChild._base_manager is ManagerTestChild._default_manager
+
     def test_default_manager(self):
         from .models import FilteredManager, FilteredManager2