[FIX] mail, mass_mailing: fix attachment ownership

Attachments that are uploaded on a record that isn't saved yet are
created with res_id set to 0. In the case of attachments linked through
a m2m rather than the usual (res_model, res_id), it means they may not
be readable afer the creation of the record, except by their creator.

Re-attaching them to the mailing / template at the end of the create()
call fixes the ownership.

Fixes #81935

closes odoo/odoo#82120

X-original-commit: 05fb705f2729ffdf07ab36accda20415a44e1aa6
Signed-off-by: Olivier Dony <odo@odoo.com>

addons/mail/models/mail_template.py

@@ -79,6 +79,15 @@ class MailTemplate(models.Model):
     # CRUD
     # ------------------------------------------------------------
 
+    @api.model_create_multi
+    def create(self, vals_list):
+        templates = super().create(vals_list)
+        # fix attachment ownership
+        for template in templates:
+            if template.attachment_ids:
+                template.attachment_ids.write({'res_model': self._name, 'res_id': template.id})
+        return templates
+
     def unlink(self):
         self.unlink_action()
         return super(MailTemplate, self).unlink()

addons/mass_mailing/models/mailing.py

@@ -417,6 +417,12 @@ class MassMailing(models.Model):
             if mailing.ab_testing_enabled and not mailing.campaign_id
         ]
         self.env['utm.campaign'].create(campaign_vals)
+
+        # fix attachment ownership
+        for mailing in mailings:
+            if mailing.attachment_ids:
+                mailing.attachment_ids.write({'res_model': self._name, 'res_id': mailing.id})
+
         return mailings
 
     def write(self, values):