[FIX] mail: improve performance of channel member_count

Forcing a fetch of all channel partners for all channels is not efficient
because there are too many of them.

Replace by a count done in SQL through `read_group`.

Time goes from 100ms to 3ms for 1000s of members in 100s of channels.

Part of task-2702450

closes odoo/odoo#81175

X-original-commit: 7c77775a84474ccdfe32bdd783291728fbfbdc42
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/models/mail_channel.py

@@ -73,7 +73,7 @@ class Channel(models.Model):
         groups='base.group_user')
     rtc_session_ids = fields.One2many('mail.channel.rtc.session', 'channel_id', groups="base.group_system")
     is_member = fields.Boolean('Is Member', compute='_compute_is_member', compute_sudo=True)
-    member_count = fields.Integer(string="Member Count", compute='_compute_member_count', help="Excluding guests from count.")
+    member_count = fields.Integer(string="Member Count", compute='_compute_member_count', compute_sudo=True, help="Excluding guests from count.")
     group_ids = fields.Many2many(
         'res.groups', string='Auto Subscription',
         help="Members of those groups will automatically added as followers. "
@@ -154,8 +154,10 @@ class Channel(models.Model):
 
     @api.depends('channel_partner_ids')
     def _compute_member_count(self):
+        read_group_res = self.env['mail.channel.partner'].read_group(domain=[('channel_id', 'in', self.ids)], fields=['channel_id'], groupby=['channel_id'])
+        member_count_by_channel_id = {item['channel_id'][0]: item['channel_id_count'] for item in read_group_res}
         for channel in self:
-            channel.member_count = len(channel.with_context(active_test=False).channel_partner_ids)
+            channel.member_count = member_count_by_channel_id.get(channel.id, 0)
 
     # ONCHANGE
 

addons/test_discuss_full/tests/test_performance.py

@@ -99,7 +99,7 @@ class TestDiscussFullPerformance(TransactionCase):
         self.maxDiff = None
         self.users[0].flush()
         self.users[0].invalidate_cache()
-        with self.assertQueryCount(emp=90):
+        with self.assertQueryCount(emp=91):
             init_messaging = self.users[0].with_user(self.users[0])._init_messaging()
 
         self.assertEqual(init_messaging, {