blender-studio/docs/resetting_migrations.md

Resetting migrations and introducing new User model

This how-to is based on a comment to ticket #25313. The reason migrations had been reset in this project are the following:

• Replacing auth.User model; which is not possible mid-project without migrations being reset;
• Simplifying test runs;
• Having a possibility of running tests with in-memory SQLite instead of PostgreSQL.

Step zero: backup your production database

Make sure you make backups of your production database.

Step one: an identical User model and initial migrations

users app

Because you probably have a multitude of FKs to the auth.User model, it's easier to create a completely separate app that will contain it. This ensures

Re-creating migrations

find . -path "*/migrations/*.py" -not -name "__init__.py" -delete
find . -path "*/migrations/*.pyc" -delete
./manage.py makemigrations

Some data migrations have to be added manually

• can_view_content to the demo and subscriber groups:

def add_can_view_content_permission_to_groups(apps, schema_editor):
    Group = apps.get_model('auth', 'Group')
    Permission = apps.get_model('auth', 'Permission')
    ContentType = apps.get_model('contenttypes', 'ContentType')
    Profile = apps.get_model('profiles', 'Profile')
    content_type = ContentType.objects.get_for_model(Profile)
    # permissions are created in a `post_migrate` signal and won't be available until the **next** ./manage.py migrate,
    # causing __fake__.DoesNotExist: Permission matching query does not exist
    permission, _ = Permission.objects.get_or_create(
        codename='can_view_content',
        content_type=content_type,
        name='Can view subscription-only content',
    )
    # Add this permission to the groups that are currently interpreted as having active subscription status
    for group_name in ('demo', 'subscriber'):
        # Create these groups, so that tests and newly setup dev environments worked as expected
        group, _ = Group.objects.get_or_create(name=group_name)
        group.permissions.add(permission)

    ...
    migrations.RunPython(add_can_view_content_permission_to_groups),
    ...

At this point testsuite should complete without issues and a commit can be made.

Deployment steps

echo 'TRUNCATE TABLE django_migrations;' | psql --dbname=postgresql://studio:PASSWORD@localhost:5432/studio
git pull
./manage.py migrate --fake

rewrite content types

Now rewrite LogEntry to keep the admin history intact:

./manage.py shell
>>>
>>> from django.contrib.admin.models import LogEntry
>>> from django.contrib.contenttypes.models import ContentType
>>>
>>> auth_user = ContentType.objects.get(app_label='auth', model='user')
>>> new_user = ContentType.objects.get(app_label='users', model='user')
>>>
>>> for le in LogEntry.objects.filter(content_type=auth_user):
...     le.content_type = new_user
...     le.save()
...
>>> from actstream.models import Action  # same for Action

>>> for le in Action.objects.filter(actor_content_type=auth_user):
>>>     le.actor_content_type = new_user
>>>     le.save()

Run this and make sure to answer NO to find more models that might need refer to ContentType that need updating:

./manage.py remove_stale_contenttypes