Admin renders complex PKs incorrectly

[David Sanders]

Admin creates links to edit/history/etc pages by rendering the PK directly as a string - either explicitly in Python or implicitly in one of the templates.

However when the instance is retrieved in get_object() it uses field.to_python(value) like so: ​https://github.com/django/django/blob/a3882876927a819ca982ea61353945e9d86f3659/django/contrib/admin/options.py#L886

This creates an asymmetrical serialisation-deserialisation process which, while is fine for integers, will fail for things more complex.

The correct serialisation of pk would be the inverse of to_python(): field.value_to_string(obj).

Note this is related to #35953: The fix for this would also be useful to get composite PKs working - at least for rendering the PK.

I noticed this while trying out DateTimeRangeField() as part of the PK for temporal models as the valid_time – this field type uses specific json serialisation which is quite verbose in the URL but works (have tested it will post proposed patch in a draft PR)

[David Sanders]

Draft PR: ​https://github.com/django/django/pull/19600

[David Sanders]

I think I've got something worth reviewing now 👍