Hi,

   we can add the manager in the employee master.Add this condition to check whether he is manager or not employee_id.parent_id.user_id.id = self._uid if this condition satisfy he can approve the request other wise raise a warning.                  

Hi Dhouha,

I am seeing the same question from you for the third time i guess. So I will repeat my answer one more time. You can either raise a warning when a manager tries to approve leaves of users who are not in his department. To do this you may use super on approve method in hr_holidays. 

Second and better way to do what you wish is to add record rules so that managers can see leaves of his employee only. Since you need to changes rules of Leaves/Manager, delete the exiting rules for that group in hr_holidays object. Then add a new record rule "[('department_id.member_ids.user_id', '=', user.id)]" and give this as domain. 

Mihran