Fixed unwanted manager replacement in Django 1.11 projects.

Django 1.11 uses the old manager inheritance system, unless it's
overwritten with manager_inheritance_from_future. With a class layout
like:

  PolymorphicModel  (abstract)
    PolymorphicMPTTModel  (abstract)
      GenericCustomer  (concrete, has objects = ...)
        CustomerGroupBase (abstract, has objects = ...)
          Partner (concrete, no manager)
            BranchPartner  (concrete, no manager)

The last level gets a normal Django Manager instead of the polymorphic
manager. Because the PolymorphicModel had a base_objects manager, this
was typically used as _default_manager. Now that the default manager is
no longer affected, it's also easier to detect why the "objects" doesn't
get the proper manager type. Using "manager_inheritance_from_future" is
recommended instead to have both the right behavior and forward
Django 2.x compatibility.

polymorphic/base.py

@@ -7,7 +7,10 @@ from __future__ import absolute_import
 import inspect
 import os
 import sys
+import warnings
 
+import django
+from django.core.exceptions import ImproperlyConfigured
 from django.db import models
 from django.db.models.base import ModelBase
 from django.db.models.manager import ManagerDescriptor
@@ -134,15 +137,40 @@ class PolymorphicModelBase(ModelBase):
         and its querysets from PolymorphicQuerySet - throw AssertionError if not"""
 
         if not issubclass(type(manager), PolymorphicManager):
-            e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" manager is of type "' + type(manager).__name__
+            if django.VERSION < (2, 0):
-            e += '", but must be a subclass of PolymorphicManager'
+                extra = "\nConsider using Meta.manager_inheritance_from_future = True for Django 1.x projects"
-            raise AssertionError(e)
+            else:
+                extra = ''
+            e = ('PolymorphicModel: "{0}.{1}" manager is of type "{2}", but must be a subclass of'
+                 ' PolymorphicManager.{extra}'.format(
+                model_name, manager_name, type(manager).__name__, extra=extra))
+            raise ImproperlyConfigured(e)
         if not getattr(manager, 'queryset_class', None) or not issubclass(manager.queryset_class, PolymorphicQuerySet):
-            e = 'PolymorphicModel: "' + model_name + '.' + manager_name + '" (PolymorphicManager) has been instantiated with a queryset class which is'
+            e = ('PolymorphicModel: "{0}.{1}" (PolymorphicManager) has been instantiated with a queryset class '
-            e += ' not a subclass of PolymorphicQuerySet (which is required)'
+                 'which is not a subclass of PolymorphicQuerySet (which is required)'.format(model_name, manager_name))
-            raise AssertionError(e)
+            raise ImproperlyConfigured(e)
         return manager
 
+    @property
+    def base_objects(self):
+        warnings.warn(
+            "Using PolymorphicModel.base_objects is deprecated.\n"
+            "Use {0}.objects.non_polymorphic() instead.".format(self.__class__.__name__),
+            DeprecationWarning)
+
+        # Create a manager so the API works as expected. Just don't register it
+        # anymore in the Model Meta, so it doesn't substitute our polymorphic
+        # manager as default manager for the third level of inheritance when
+        # that third level doesn't define a manager at all.
+        manager = models.Manager()
+        manager.name = 'base_objects'
+        manager.model = self
+        return manager
+
+    @property
+    def _default_manager(self):
+        if len(sys.argv) > 1 and sys.argv[1] == 'dumpdata':
+            # TODO: investigate Django how this can be avoided
             # hack: a small patch to Django would be a better solution.
             # Django's management command 'dumpdata' relies on non-polymorphic
             # behaviour of the _default_manager. Therefore, we catch any access to _default_manager
@@ -151,16 +179,14 @@ class PolymorphicModelBase(ModelBase):
             # (non-polymorphic default manager is 'base_objects' for polymorphic models).
             # This way we don't need to patch django.core.management.commands.dumpdata
             # for all supported Django versions.
-    if len(sys.argv) > 1 and sys.argv[1] == 'dumpdata':
-        # manage.py dumpdata is running
-
-        def __getattribute__(self, name):
-            if name == '_default_manager':
             frm = inspect.stack()[1]  # frm[1] is caller file name, frm[3] is caller function name
             if DUMPDATA_COMMAND in frm[1]:
                 return self.base_objects
-                # caller_mod_name = inspect.getmodule(frm[0]).__name__  # does not work with python 2.4
-                # if caller_mod_name == 'django.core.management.commands.dumpdata':
 
-            return super(PolymorphicModelBase, self).__getattribute__(name)
+        manager = super(PolymorphicModelBase, self)._default_manager
-    # TODO: investigate Django how this can be avoided
+        if not isinstance(manager, PolymorphicManager):
+            warnings.warn("{0}._default_manager is not a PolymorphicManager".format(
+                self.__class__.__name__
+            ), RuntimeWarning)
+
+        return manager

polymorphic/models.py

@@ -54,7 +54,6 @@ class PolymorphicModel(six.with_metaclass(PolymorphicModelBase, models.Model)):
     # Note that Django 1.5 removes these managers because the model is abstract.
     # They are pretended to be there by the metaclass in PolymorphicModelBase.get_inherited_managers()
     objects = PolymorphicManager()
-    base_objects = models.Manager()
 
     class Meta:
         abstract = True

polymorphic/query.py

@@ -379,7 +379,7 @@ class PolymorphicQuerySet(QuerySet):
         # Then we copy the extra() select fields from the base objects to the real objects.
         # TODO: defer(), only(): support for these would be around here
         for real_concrete_class, idlist in idlist_per_model.items():
-            real_objects = real_concrete_class.base_objects.db_manager(self.db).filter(**{
+            real_objects = real_concrete_class.objects.non_polymorphic().using(self.db).filter(**{
                 ('%s__in' % pk_name): idlist,
             })
             real_objects.query.select_related = self.query.select_related  # copy select related configuration to new qs

polymorphic/tests/models.py

@@ -191,7 +191,9 @@ class MROBase1(ShowFieldType, PolymorphicModel):
 
 
 class MROBase2(MROBase1):
-    pass  # Django vanilla inheritance does not inherit MyManager as _default_manager here
+    class Meta:
+        # Django 1.x inheritance does not inherit MyManager as _default_manager here
+        manager_inheritance_from_future = True
 
 
 class MROBase3(models.Model):
@@ -200,7 +202,8 @@ class MROBase3(models.Model):
 
 
 class MRODerived(MROBase2, MROBase3):
-    pass
+    class Meta:
+        manager_inheritance_from_future = True
 
 
 class ParentModelWithManager(PolymorphicModel):