I have two selectbox field in the form employee and department. I want to pick department automatically when I pick employee according to employee's department_id.

Here is my .py code (Odoo 11)

class HrExpenseExpense(models.Model):
_inherit = "hr.expense"

department_expense_group = fields.Selection(
    string='Department Expense Group',
    related='department_id.expense_group',
    readonly=True,
)
department_id = fields.Many2one('hr.department', string='Department',
                                states={'post': [('readonly', True)], 'done': [('readonly', True)]})

@api.onchange('employee_id')
def onchange_employee_id(self):
    department_id = [x.id for x in self.employee_id.department_id]
    return {'domain': {'department_id': [('id', 'in', department_id)]}}

And xml view file:

 <xpath expr="//field[@name='employee_id']" position="after">
   <field name="department_expense_group" invisible="1" />
   <field name="department_id" invisible="0"/>
 </xpath>

It's working but problem is this; when I pick an employee, department selectbox updating automatically, it's triggering but not selecting automatically. Selectbox's list filling after I click to it. It must be selected automatically according to employee choice.

Thank you for help!