[17.0, 16.0] formio.form model: Many2oneReference (res_model, res_id) to replace specialized model FK

[bobslee]

SYNOPSIS

To improve (and ease) the generic integration of forms, it's maybe possible to replace this by the generic Many2oneReference field.
(Possible v16.0 work).

Research and refactor formio.form model resource implementation to use the Many2oneReferene pseudo field.

This concerns the already present fields res_model, res_id etc (other res_ fields).

This results into 2 fields in the formio_form table, eg:

Column    | Type
-----------------------------
res_model | character varying
res_id    | integer

Docs (ORM API, reference)

See: https://www.odoo.com/documentation/16.0/developer/reference/backend/orm.html#odoo.fields.Many2oneReference
Examples of implementation: mail.activity, mail.followers, mail.message.

REQUIREMENTS

So this thoroughly requires:

• Design choices (eg. also options on delete of the resource/related model: block, set null, cascade).
• Testing (proof of concept with 1 module, eg formio_crm)
• Refactoring (and probably support the old-style field, due to past custom implementations eg by server actions etc)
• Probably a migration scrript

WARNINGS (to test):

• However, still in specialized modules (eg formio_crm) the FK in the formio.form model is the specialized one (eg. crm_lead_id). See also above regarding "refactoring old-style" and "migration script".
• Views (eg. crm_lead_views.xml): Action button formio.action_formio_form context (fields).