Model breaks NetBox upgrade script (remove_stale_contenttypes step) if field references another custom object

[averyhabbott]

Plugin Version

0.1.0

NetBox Version

4.3.4

Python Version

3.12.7

Steps to Reproduce

Run "sudo ./opt/netbox/upgrade.sh"
Doesn't matter whether or not you have a new version of NetBox staged

Expected Behavior

Upgrade script runs successfully

Observed Behavior

Script fails during "remove_stale_contenttypes" step

Removing stale content types (python3 netbox/manage.py remove_stale_contenttypes --no-input)...
Traceback (most recent call last):
  File "/opt/netbox-4.3.5/netbox/manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 436, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/core/management/base.py", line 416, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/core/management/base.py", line 460, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/contrib/contenttypes/management/commands/remove_stale_contenttypes.py", line 102, in handle
    ct.delete()
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/db/models/base.py", line 1280, in delete
    collector.collect([self], keep_parents=keep_parents)
  File "/opt/netbox-4.3.5/venv/lib/python3.12/site-packages/django/db/models/deletion.py", line 350, in collect
    raise ProtectedError(
django.db.models.deletion.ProtectedError: ("Cannot delete some instances of model 'ContentType' because they are referenced through protected foreign keys: 'CustomObjectTypeField.related_object_type'.", {<CustomObjectTypeField: DHCP Environment>})

[averyhabbott]

After some more testing, this only happens if I have a field with type object that points to another custom object type. In hindsight, this was in the last line of the error above. I've updated the issue title to reflect this information.

Use case:
I have multiple DHCP environments (prod, non-prod, etc) and tons of DHCP scopes. I created a custom object type for the DHCP Environment with fields like name, primary server URL, backup server URL, etc., and another custom object type for the DHCP Scope with fields like prefix (object), start IP, and end IP. One of the fields in the DHCP Scope is the DHCP Environment so I know where the scope should be provisioned. My plan was to also leverage the custom object types for DHCP Option definitions and have that as a multi-object select on the DHCP Scope.

[mrmrcoleman]

Tested at:

NetBox version: commit b4c88541da32d38c1634211cdb614ef0a7e58819 (HEAD, origin/feature, feature)
Custom Objects version: commit 7231f9fa505801c6c689c03b4946d84a0052cc81 (HEAD -> feature, origin/feature)

What I think is happening

The NetBox upgrade script fails during the remove_stale_contenttypes step when a CustomObjectTypeField has a related_object_type that references a ContentType Django considers "stale" and wants to remove.

The CustomObjectTypeField.related_object_type field has a protected foreign key relationship to Django's ContentType model. When Django's remove_stale_contenttypes management command tries to delete ContentTypes that are no longer present in the codebase, it fails because these ContentTypes are still referenced by custom object fields.

Error Message

django.db.models.deletion.ProtectedError: ("Cannot delete some instances of model 'ContentType' because they are referenced through protected foreign keys: 'CustomObjectTypeField.related_object_type'.", {<CustomObjectTypeField: DHCP Environment>})

Steps to Reproduce

1. Create a custom object with a field referencing another object type:

   # Create custom object type
   curl -X POST "http://localhost:8000/api/plugins/custom-objects/custom-object-types/" \
     -H "Authorization: Token YOUR_TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"name": "Test Object", "description": "Test object for bug reproduction"}'
   
   # Create field that references another object type (e.g., circuits.provider)
   curl -X POST "http://localhost:8000/api/plugins/custom-objects/custom-object-type-fields/" \
     -H "Authorization: Token YOUR_TOKEN" \
     -H "Content-Type: application/json" \
     -d '{
       "name": "testobject",
       "custom_object_type": 1,
       "type": "object",
       "related_object_type": 38
     }'

2. Verify the relationship exists:

   docker compose exec netbox python3 /opt/netbox/netbox/manage.py shell -c "
   from netbox_custom_objects.models import CustomObjectTypeField
   for field in CustomObjectTypeField.objects.filter(related_object_type__isnull=False):
       print(f'Field: {field.name} -> ContentType ID: {field.related_object_type_id}')
   "

3. Reproduce the error by simulating the upgrade scenario:

   docker compose exec netbox python3 /opt/netbox/netbox/manage.py shell -c "
   from netbox_custom_objects.models import CustomObjectTypeField
   from django.contrib.contenttypes.models import ContentType
   from django.db.models.deletion import ProtectedError
   
   # Find field with reference
   field = CustomObjectTypeField.objects.filter(related_object_type__isnull=False).first()
   ct = ContentType.objects.get(id=field.related_object_type_id)
   
   # Try to delete ContentType (simulates remove_stale_contenttypes)
   try:
       ct.delete()
   except ProtectedError as e:
       print('ProtectedError:', e)
   "

4. Run the actual problematic command:

   docker compose exec netbox python3 /opt/netbox/netbox/manage.py remove_stale_contenttypes --no-input

Output

Test Output:

Found field: testobject referencing ContentType ID: 38
Referenced ContentType: circuits.provider
ProtectedError occurred: ("Cannot delete some instances of model 'ContentType' because they are referenced through protected foreign keys: 'ObjectType.contenttype_ptr'.", {<CustomObjectTypeField: Testobject>})

[arthanson]

@mrmrcoleman can you please try this against main. I do the following:

1. create custom object type cot1
2. create field f1 type text on cot1
3. add a CO of cot1 "aaa"
4. create custom object type cot2
5. create field on cot2 of type Object pointing to cot1
6. run manage.py remove_stale_contenttypes --no-input

Works fine. tried it with creating an object of type cot2 and deleting the COTs but the command still ran fine.

[mrmrcoleman]

Tested at:

NetBox version: commit 6d4cc16ca41e472615b6a061afc3f864a60248dc (HEAD, tag: v4.4.0-beta1)
Custom Objects version: commit 7a42cf8174669522baf02a298950078efa31a612 (HEAD -> main, origin/main, origin/HEAD)

---

Fixed in upcoming release