Before https://github.com/OCA/data-protection/pull/29 there was a race condition where an email could be sent while the same transaction that created the `privacy.consent` record still wasn't committed, producing a 404 error if the user clicked on "Accept" or "Reject" before all mails were sent.
To avoid that, a raw `cr.commit()` was issued, but this produced another situation where the user had to wait until the full email queue is cleared to get his page loaded. It wasn't an error, but a long queue meant several minutes waiting, and it's ulikely that an average human is so patient.
So, here's the final fix (I hope!). The main problem was that I was looking in the wrong place to send the email. It turns out that the `self.post_message_with_template()` method is absolutely helpless in the case at hand, where these criteria must be met:
* E-mail must be enqueued, no matter if there are less or more than 50 consents to send.
* The template must be processed per record.
* In an ideal world, a `cr.commit()` must be issued after each sent mail.
The metod that was being used:
* Didn't allow to use `auto_commit` mode.
* Only allowed to render the template per record if called with `composition_mode="mass_mail"`.
* Only allowed to enqueue emails if called with `composition_mode="mass_post"`.
Obviously, I cannot set 2 different values for `composition_mode`, so a different strategy had to be used.
I discovered that the `mail.template` model has a helpful method called `send_mail()` that, by default:
* Renders the template per record
* Enqueues the email
* The email queue is cleared in `auto_commit=True` mode.
So, from now on, problems are gone:
* The user click, or the cron run, will just generate the missing `privacy.consent` records and enqueue mails for them.
* The mail queue manager will send them later, in `auto_commit` mode.
* After sending the e-mail, this module will set the `privacy.consent` record as `sent`.
* Thanks to *not* sending the email, the process the user faces when he hits the "generate" button is faster.
* Instructions in the README and text in the "generate" button are updated to reflect this new behavior.
* Thanks to the `auto_commit` feature, if Odoo is rebooted in the middle of a mail queue clearance, the records that were sent remain properly marked as sent, and the missing mails will be sent after the next boot.
* No hardcoded commits.
* No locked transactions.
* BTW I discovered that 2 different emails were created when creating a new consent. I started using `mail_create_nolog=True` to avoid that problem and only log a single creation message.
Note to self: never use again `post_message_with_template()`.
Jairo Llopis
OCA Git Bot
Nicolas JEUDY