[FIX] mass_mailing_partner: optimize duplicates check and error message

[yajo]

Code is simpler, it benefits from ORM cache (which is helpful because checks are done before flushing), and the error message now tells problematic partners.

@moduon MT-13677

[Shide]

Code review

[pedrobaeza]

Please check OCA/social#1830 that is pending to be fw-ported.

[yajo]

I find it strange that you just removed such feature... Could you elaborate a bit on why?

[pedrobaeza]

Because it's a legacy check before Odoo changed the way mass mailing contacts are handled. If you check on runbot, Odoo allows to have several mailing contacts in the same list with the same email. When sending the mailing, it will be sent only once (there's an email deduplication). Artificially prevent these duplicates only complicates the user management and provokes to the user a lot of friction. Examples:

• An email in a contact linked to a mass mailing contact is changed, and that one is the same as another.
• You do a mass contact import into a mailing list. You will get error if several contacts of that selection have the same email.
• etc

Thus, it's better to remove that artificial restriction. The only trade-off is that the sent mass mailings will be linked to the first contact found, but that's something reasonable.

[yajo]

Thanks for the explanation! Then, indeed that's the proper solution.

I can't believe this passed under our radar since v15: odoo/odoo#61467