function add_grn(&$po, $date_, $reference, $location)
{
function add_grn(&$po, $date_, $reference, $location)
{
begin_transaction();
$grn = add_grn_batch($po->order_no, $po->supplier_id, $reference, $location, $date_);
begin_transaction();
$grn = add_grn_batch($po->order_no, $po->supplier_id, $reference, $location, $date_);