Commit f8b41da4 authored by Simon Charette's avatar Simon Charette Committed by Aymeric Augustin
Browse files

[1.5.x] Fixed #19688 -- Allow model subclassing with a custom metaclass using six.with_metaclass 

Backport of 6b03179e from master.

Although we're post RC 2, I'm backporting this because it's arguably a
major bug in a new feauture that will prevent several well-known
third-party apps from being ported to Python 3.
parent 1845c530

django/db/models/base.py

+11 −2
Original line number Diff line number Diff line
@@ -58,12 +58,21 @@ class ModelBase(type): 
    """

    def __new__(cls, name, bases, attrs):

        super_new = super(ModelBase, cls).__new__



        # six.with_metaclass() inserts an extra class called 'NewBase' in the

        # inheritance tree: Model -> NewBase -> object. Ignore this class.

        # inheritance tree: Model -> NewBase -> object. But the initialization

        # should be executed only once for a given model class.



        # attrs will never be empty for classes declared in the standard way

        # (ie. with the `class` keyword). This is quite robust.

        if name == 'NewBase' and attrs == {}:

            return super_new(cls, name, bases, attrs)



        # Also ensure initialization is only performed for subclasses of Model

        # (excluding Model class itself).

        parents = [b for b in bases if isinstance(b, ModelBase) and

                not (b.__name__ == 'NewBase' and b.__mro__ == (b, object))]

        if not parents:

            # If this isn't a subclass of Model, don't do anything special.

            return super_new(cls, name, bases, attrs)



        # Create the class.

tests/modeltests/base/__init__.py

0 → 100644
+0 −0

Empty file added.

tests/modeltests/base/models.py

0 → 100644
+5 −0
Original line number Diff line number Diff line 
from django.db.models.base import ModelBase





class CustomBaseModel(ModelBase):

    pass

tests/modeltests/base/tests.py

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+36 −0
Original line number Diff line number Diff line 
from __future__ import unicode_literals



from django.db import models

from django.test.testcases import SimpleTestCase

from django.utils import six

from django.utils.unittest import skipIf



from .models import CustomBaseModel





class CustomBaseTest(SimpleTestCase):



    @skipIf(six.PY3, 'test metaclass definition under Python 2')

    def test_py2_custom_base(self):

        """

        Make sure models.Model can be subclassed with a valid custom base

        using __metaclass__

        """

        try:

            class MyModel(models.Model):

                __metaclass__ = CustomBaseModel

        except Exception:

            self.fail("models.Model couldn't be subclassed with a valid "

                      "custom base using __metaclass__.")



    def test_six_custom_base(self):

        """

        Make sure models.Model can be subclassed with a valid custom base

        using `six.with_metaclass`.

        """

        try:

            class MyModel(six.with_metaclass(CustomBaseModel, models.Model)):

                pass

        except Exception:

            self.fail("models.Model couldn't be subclassed with a valid "

                      "custom base using `six.with_metaclass`.")