Unexpected on_delete behavior in apps that have been removed from INSTALLED_APPS

[Tobias Bengfort]

If I remove an app from INSTALLED_APPS that contains models with ForeignKeys to other apps, the python-level on_delete is removed but the database level foreign key constraint still exists. The residual ForeignKeys can then block the deletion of other content.

I guess the proper way to deal with this is to drop all tables belonging to the removed app. There should be a warning about this in the documentation.

An alternative approach could be to allow database-level on_delete (see 21961)

[Mariusz Felisiak]

Thanks for the ticket, however I don't see anything unexpected in the current behavior. You removed an app from INSTALLED_APPS without reverting all applied migrations for that app, so tables, relations, etc. still exist in the database. There is nothing Django can do automatically in this case.

There should be a warning about this in the documentation.

As it stands it is a usage issue. I don't see it as really common enough to justify a warning in docs.