Getting model ContentType in migration - Django 1.7

Question

I have a data migration that updates some permissions. I know there are some known issues with permissions in migrations and i was able to avoid some trouble by creating the permissions in the migration it self (rather then using the tuple shortcut in the model).

The migration :

from __future__ import unicode_literals
from django.db import migrations, models
from django.conf import settings

def create_feature_groups(apps, schema_editor):
    app = models.get_app('myauth')

    Group = apps.get_model("auth", "Group")
    pro = Group.objects.create(name='pro')

    Permission = apps.get_model("auth", "Permission")
    ContentType = apps.get_model("contenttypes", "ContentType")
    invitation_contenttype = ContentType.objects.get(name='Invitation')

    send_invitation = Permission.objects.create(
         codename='send_invitation',
         name='Can send Invitation',
         content_type=invitation_contenttype)

    pro.permissions.add(receive_invitation)    

class Migration(migrations.Migration):

    dependencies = [
        ('myauth', '0002_initial_data'),
    ]

    operations = [
            migrations.RunPython(create_feature_groups),
    ]

After some trial and error i was able to make this work using manage.py migrate but i'm getting errors in the test manage.py test.

__fake__.DoesNotExist: ContentType matching query does not exist.

Debugging a bit discovered that there are no ContentType at this point in the migration when run in test (not sure why). Following the advice in this post i tried updating the content types manually in the migration it self. Added :

from django.contrib.contenttypes.management import update_contenttypes
update_contenttypes(app, models.get_models())

before fetching the content type for the Invitation model. Got the following error

  File "C:\Python27\lib\site-packages\django-1.7-py2.7.egg\django\contrib\contenttypes\management.py", line 14, in update_contenttypes
    if not app_config.models_module:
AttributeError: 'module' object has no attribute 'models_module'

There must be some way to create/update permissions in data migrations in a testable way.

Thanks.

EDIT

Finally made it work by adding

from django.contrib.contenttypes.management import update_all_contenttypes
update_all_contenttypes() 

oddly enough this one was not sufficient

update_contenttypes(apps.app_configs['contenttypes'])

I would love to know why all of this is necessary

Answer 1

For Django 2.1 I had to import apps from global registry because passed apps into migration were instances of django.db.migrations.state.AppConfigStub without populated models_module attribute. And create_contenttypes is checking this attribute.

from django.apps.registry import Apps, apps as global_apps
from django.contrib.contenttypes.management import create_contenttypes
from django.db import migrations


def add_permision(apps: Apps, schema_editor):
    my_app_config = global_apps.get_app_config('my_app')
    create_contenttypes(my_app_config)

    ...

Answer 2

The answer is:

apps.get_model('contenttypes', 'ContentType') 

:) Needed it myself today.

Answer 3

Having a similar issue when writing a data migration that spans several apps. Turns out Django only loads those models into the app registry that are affected by what the "dependencies" member of the migration states: https://code.djangoproject.com/ticket/24303

Had to basically add an entry to the migration dependencies that I use that is not directly related by e.g. a ForeignKey to the app that is currently being migrated.