JSONField are not properly displayed in admin when they are readonly.

[Gagaro]

JSONField values are displayed as dict when readonly in the admin.

For example, {"foo": "bar"} would be displayed as {'foo': 'bar'}, which is not valid JSON.

I believe the fix would be to add a special case in django.contrib.admin.utils.display_for_field to call the prepare_value of the JSONField (not calling json.dumps directly to take care of the InvalidJSONInput case).

[dbxnr]

​PR

[Simon Charette]

The proposed patch is problematic as the first version coupled contrib.postgres with .admin and the current one is based off the type name which is brittle and doesn't account for inheritance.

It might be worth waiting for #12990 to land before proceeding here as the patch will be able to simply rely of django.db.models.JSONField instance checks from that point.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 675ce4d:

Refs #31157 -- Added tests for display_for_field() with empty JSONField.

[Mariusz Felisiak <felisiak.mariusz@…>]

In fc0f7f6c:

Fixed #31157 -- Fixed displaying read-only JSONField values in admin.