Create (or change) a model to use UUID/non-integer for its primary key

[lb-]

Problem

We often get bugs raised for models that use a non-integer primary key.

This creates a few issues with our code assumptions

• Converting to a string for element ID usage or similar can have problems
• Using some_instance.id will not work and needs to.be replaced with some_instance.pk
• Assumptions about general ordering of thing in code can be false

Proposal

Assuming we can use a migration to modify existing models, that would be best as it avoids trying to think of new example data.

1. breads.Country - Change to a non-integer primary key of a two letter string. E.g. 'AU', that's set on creation of any new entries, but will not be editable (read only but visible in the UI on edit).
2. breads.BreadIngredient - Change to a non-integer primary key that's an auto-generated UUID (or BreadType). Not visible in the UI.

This way we are only changing models in one app and have a cross-section of UI interaction (choosers, snippet listing, history etc).

Related issues & PRs

Many are closed, but retesting this is often tricky and it would be great if we had a model ready to go. Plus, if problems like these are more visible we may find them earlier.

• SnippetChooserPanel is broken with UUID primary keys wagtail#10856
• Revisions for a copied page do not update PKs recursively for related models wagtail#8242 (potentially)
• Bulk actions makes false assumption that ids will always be a number wagtail#8563
• User primary key UUID and wagtail 2.13 comments wagtail#7235
• CommentPanel does not allow user.pk to be of type UUID wagtail#7206
• Primary keys are cast instead of relying on serialization wagtail#6512
• Wagtail must use "pk" instead "id" for users models wagtail#2347
• Reorganise snippet admin URLs to avoid ambiguous paths wagtail#7208
• Update snippets so that they can handle custom primary keys (rebase of #4003) wagtail#4166
• Allow ModelViewSet to be used for models with non-integer primary keys wagtail#10900

[laymonage]

Change to a non-integer primary key of a two letter string. E.g. 'AU' that's user editable.

Just to note – primary keys are read-only:

https://docs.djangoproject.com/en/4.2/ref/models/fields/#primary-key

The primary key field is read-only. If you change the value of the primary key on an existing object and then save it, a new object will be created alongside the old one.

[lb-]

Ahh. Good point @laymonage - I'll fix that.