[16.0][IMP] account: migrate bank statement chatter attachments to attachment_ids

[CarlosRoca13]

In Odoo 16, account.bank.statement gains a new attachment_ids many2many field to ir.attachment. Add a post-migration query that links the existing chatter attachments (ir.attachment with res_model = 'account.bank.statement') into this field.

cc @Tecnativa TT63091

ping @pedrobaeza @sergio-teruel

[pedrobaeza]

But where these attachments come from? It's an OCA module?

[sergio-teruel]

Before version 16.0, the account.bank.statement model inherited from mail.thread, so users could attach files directly to the statement record through the chatter.

Starting from 16.0, this model no longer inherits from mail.thread, so the previous attachments are no longer visible through the chatter. However, Odoo added the attachment_ids field directly on the model here:

https://github.com/odoo/odoo/blob/f95bcc097fd7e70af8d28a66c010ae9b9490f439/addons/account/models/account_bank_statement.py#L100

In addition, account_statement_base already exposes this field in the form view using the many2many_binary widget:

https://github.com/OCA/account-reconcile/blob/18.0/account_statement_base/views/account_bank_statement.xml#L83

So I think there are two possible approaches:

1. Restore the chatter by inheriting from mail.thread again and adding the chatter back to the view.
2. Do not restore the chatter, but migrate/recreate the relation between the bank statements and their existing attachments so they are available through the current attachment_ids field.

Personally, I would prefer option 2, because it keeps the current Odoo design and avoids reintroducing the chatter only for attachment visibility.

[pedrobaeza]

Understood. Thanks for the clarifications. They may be in the commit message, but let's not block it.