id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
26605	Abstract model inheriting concrete model crashes migrations	Sébastien Diemer	Akshesh Doshi	"When using Model inheritance with an abstract model in between, it can happen that the _default_manager of the actual child class is None. In this case the //ModelState.from_model// function fails with the following error:
{{{
django/django/db/migrations/state.py"", line 439, in from_model
    default_manager_name = force_text(model._default_manager.name)
AttributeError: 'NoneType' object has no attribute 'name'
}}}

The following modified test reproduces the error:
{{{
    @override_settings(TEST_SWAPPABLE_MODEL='migrations.SomeFakeModel')
    def test_create_swappable(self):
        """"""
        Tests making a ProjectState from an Apps with a swappable model
        """"""
        new_apps = Apps(['migrations'])

        class Base(models.Model):
            pass

        class AbstractAuthor(Base):
            class Meta:
                abstract = True

        class Author(AbstractAuthor):
            name = models.CharField(max_length=255)
            bio = models.TextField()
            age = models.IntegerField(blank=True, null=True)

            class Meta(AbstractAuthor.Meta):
                app_label = 'migrations'
                apps = new_apps
                swappable = 'TEST_SWAPPABLE_MODEL'

        author_state = ModelState.from_model(Author)
        self.assertEqual(author_state.app_label, 'migrations')
        self.assertEqual(author_state.name, 'Author')
        self.assertEqual([x for x, y in author_state.fields], ['id', 'name', 'bio', 'age'])
        self.assertEqual(author_state.fields[1][1].max_length, 255)
        self.assertEqual(author_state.fields[2][1].null, False)
        self.assertEqual(author_state.fields[3][1].null, True)
        self.assertEqual(author_state.options, {'abstract': False, 'swappable': 'TEST_SWAPPABLE_MODEL'})
        self.assertEqual(author_state.bases, (models.Model, ))
        self.assertEqual(author_state.managers, [])
}}}

Changing the following line in //ModelState.from_model//
{{{
        if hasattr(model, ""_default_manager""):
}}}
to
{{{
       if getattr(model, ""_default_manager"", None):
}}}
is probably sufficient to fix the bug.

See also PR https://github.com/django/django/pull/6847"	Bug	assigned	Migrations	1.8	Normal			diemersebastien@…	Accepted	1	0	1	0	0	0