her i compute field value:

@api.depends('item_type', 'link_with_stock_picking', 'link_with_service_requisition')
def _get_record_state(self):
    self.ensure_one()
    for rec in self:
        po_states = []
        service_state = []
        po_done_state = ['cancel', 'done']
        po_waiting_state = ['draft', 'assigned', 'confirmed', 'waiting']
        service_done_state = ['done', 'cancel']
        service_waiting_state = ['draft']
        if len(rec.link_with_stock_picking) > 0 and rec.item_type == 'material':
            for picking_record in rec.link_with_stock_picking:
                po_states.append(picking_record.state)
                check_state_one = any(item in po_states for item in po_waiting_state)
                if check_state_one == True:
                    rec.record_state = 'waiting_for_bill'
                else:
                    check_state_tow = any(item in po_states for item in po_done_state)
                    if check_state_tow == True:
                        rec.record_state = 'done'
        if len(rec.link_with_service_requisition) > 0 and rec.item_type == 'service':

            for service_record in rec.link_with_service_requisition:
                service_state.append(service_record.state)
                check_service_state = any(item in service_state for item in service_waiting_state)
                if check_service_state == True:
                    rec.record_state = 'waiting_for_bill'
                else:
                    check_service_state_tow = any(item in service_state for item in service_done_state)
                    print(check_service_state_tow)
                    if check_service_state_tow == True:
                        rec.record_state = 'done'
        if rec.item_type == 'material' and not rec.link_with_stock_picking:
            rec.record_state = 'draft'
        else:
            if rec.item_type == 'service' and not rec.link_with_service_requisition:
                rec.record_state = 'draft'
then i added this computed field in  tree view,
when test it i get:
ValueError: Expected singleton: model.model(22, 23)

i tried @api.one & self.ensure_one() & limit=1 in search method but still getting the error
any idea how to work around this error
Thanks