Migration fails on NetBox Branching due to duplicate Custom Field (`serializer`)

[aoforb]

Validity Version

3.3.2

NetBox Version

4.4.6

Python Version

3.10

Steps to Reproduce

Validity’s squashed initial migration (0010_squashed_initial) tries to create a Custom Field named serializer even though it already exists in the shared database.

Branching replays migrations per branch, but the database is global, so uniqueness constraints apply across all branches.

Expected Behaviour

Migration should be idempotent and skip creating Custom Fields that already exist.

1. Have an existing branch
2. Install Validity
3. Go to UI Branching, select branch click Migrate button

Traceback

Error Message
IntegrityError('duplicate key value violates unique constraint "extras_customfield_name_key"\nDETAIL: Key (name)=(serializer) already exists.')

Log Message
{
    "log": [
        "Migrating branch core-switch-refresh (branch_7a6mf5u3)",
        "Setting branch status to migrating",
        "Applying migration validity.0010_squashed_initial",
        "duplicate key value violates unique constraint \"extras_customfield_name_key\"\nDETAIL:  Key (name)=(serializer) already exists."
    ]
}

[aoforb]

Although I was not using docker before, I get the same problem on a fresh install with the docker container.

[amyasnikov]

Hi,

Django migrations are not supposed to be idempotent, so it's not the point.

I don't know how branching plugin works, perhaps I should look at the code. It might be their issue as well as it might be mine.

Could you check the same behaviour with another plugin which imposes custom fields inside its migrations as well?

[cruse1977]

This is due to, (as you've identified) custom fields not operating in branches - and the validity custom fields being created in a migration (which makes it easier for the user); until this feature may/may not be available, it may be worth a warning on the install docs to ensure branches are deleted/archived/merged prior to installation to prevent the issue.