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
There's an abstract model inheriting a concrete one in
tests/model_inheritance_regress/models.pyso this seems to be a supported use case. A regression test might go intests/migrations/test_state.py.