Deleting regions not possible if media library has nested structure

[timobrembeck]

Describe the Bug

Normally, media files and directories are cascade deleted when regions are deleted.
However, this fails if the protection rules between media files and directories prevent the cascade deletion.

Steps to Reproduce

1. Create nested directory structure with media elements in subfolders
2. Try to delete region
3. See error

Expected Behavior

The region should be deleted and all media elements and directories with it.
This can either be achieved by deleting them in the correct order (by deleting the sub-folders and elements first) or removing the protected relationship by setting parent = None on all directories and parent_directory = None on all media files before deleting.

Actual Behavior

A ProtectedError occurs

Additional Information

Traceback

Oct 12 08:25:05 ERROR   django.request - 500 Internal Server Error: /regions/saarbrückenalt/delete/
Traceback (most recent call last):
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/core/handlers/exception.py", line 47, in inner
  response = get_response(request)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/core/handlers/base.py", line 181, in _get_response
  response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/views/decorators/http.py", line 40, in inner
  return func(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
  return view_func(request, *args, **kwargs)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/integreat_cms/cms/views/regions/region_actions.py", line 46, in delete_region
  deleted_objects = region.delete()
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/db/models/base.py", line 966, in delete
  collector.collect([self], keep_parents=keep_parents)
File "/opt/integreat-cms/.venv/lib/python3.9/site-packages/django/db/models/deletion.py", line 302, in collect
  raise ProtectedError(
django.db.models.deletion.ProtectedError: ("Cannot delete some instances of model 'Region' because they are referenced through protected foreign keys: 'Director
y.region'.", {<MediaFile (id: 66048, name: arriving.png, path: /var/www/integreat-cms/media/regions/252/2022/06/arriving.png, Landeshauptstadt Saarbrücken (alt)
(&#9888; Versteckt))>})