[IMP] add record_id on mail.message to be able to access to the record

mail_usability/__init__.py

@@ -3,3 +3,4 @@
 from . import mail
 from . import tools
 from . import mail_template
+from . import mail_message

mail_usability/mail_message.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 Akretion (http://www.akretion.com).
+# @author Sébastien BEAU <sebastien.beau@akretion.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from openerp import api, fields, models
+
+
+class MailMessage(models.Model):
+    _inherit = 'mail.message'
+
+    @property
+    def record_id(self):
+        # we do not use a reference field here as mail message
+        # are used everywhere and many model are not yet loaded
+        # so odoo raise exception
+        self.ensure_one()
+        return self.env[self.model].browse(self.res_id)