[FIX] im_livechat: performance issue: slow to open dashboard of livechat channels

closes odoo/odoo#39154

X-original-commit: 6a08db92769da82023d25d04072027f8a54659b8
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/im_livechat/models/im_livechat_channel.py

@@ -70,8 +70,10 @@ class ImLivechatChannel(models.Model):
 
     @api.depends('channel_ids')
     def _compute_nbr_channel(self):
+        data = self.env['mail.channel'].read_group([('livechat_channel_id', 'in', self._ids)], ['__count'], ['livechat_channel_id'], lazy=False)
+        channel_count = {x['livechat_channel_id'][0]: x['__count'] for x in data}
         for record in self:
-            record.nbr_channel = len(record.channel_ids)
+            record.nbr_channel = channel_count.get(record.id, 0)
 
     # --------------------------
     # Action Methods