I am trying  to set state of another table while certain field is greater than a constant. But when I call method to change state another table, It does not work.

    @api.multi
    @api.depends('act_wt', 'a_wt')
    def calc_diff(self):
        self.wt_diff=0.0
        if self.state == 'aload':
            self.wt_diff = float(self.a_wt) - float(self.act_wt)
            if self.wt_diff > 5:
                self.reject_pack()
                self.state = 'reject'
    @api.multi
    def reject_pack(self):
        self.ensure_one()
        rec = self.env['pack.packing'].search([('so_no', '=', self.so_no)])
        if rec:
            rec.state = 'rejected'
With this code method works with (self.state = 'reject') but doesnot work with self.reject_pack()