Registration plugin flow could be more developer friendly

[sergei-maertens]

Thema / Theme

Plugins

Omschrijving / Description

The registration flow was broken up recently into more steps:

1. pre-registration
2. generate PDF
3. main registration

but the base plugin classes have not been updated appropriately.

I've developed a plugin for a registration service that generates its own references. This requires me to use the hook pre_register_submission and store the reference + relevant data directly on the submission model:

        submission.registration_result = {
            "id": data["id"],
            "reference": data["reference"],
            "qrcode_data": data["qrcode_data"],
        }
        submission.public_registration_reference = data["reference"]
        submission.save()

The previous API (register_submission and get_reference_from_result) did not rely on internals - instead I could reason 100% in terms of what my registration backend returns.

To make matters worse, get_reference_from_result and register_submission no longer have any purpose - all my registration is already done in the pre-registration hook, but the base plugin class enforces me to implement these two methods.

Looking at the test suite, there are many tests that call get_reference_from_result directly, but this method isn't really called anymore during the registration flow, the expectation is that a reference is set and saved during pre-registration (as the PDF generation tries to read it, which runs after pre-registration!)

Added value / Toegevoegde waarde

1. Better developer experience for registration plugin developers
2. Backwards compatibility (my existing plugin was now broken after updating to latest open forms)

Aanvullende opmerkingen / Additional context

I think it'd make sense to expect pre_register_submission return a RegistrationResult dataclass, which has result: dict and reference: str fields (optional). The tasks should then extract that information and save it on the submission.

It would probably also still be nice to call the get_reference_from_result hook after running pre-registration, instead of expecting the plugin to set the field value directly on the model.

Finally, register_submission should probably receive an explicit result field, as the pre-registration task may need to store temporary data and do the expensive processing after PDF generation.