Search custom ProductFields during Productsearch

If you create an Invoice you could use the great Search function to select products.
But what to do, if you store your unique product selector in a field, which won't be searched during this function?
You probably could apply the following modification:

But you probably will need some SQL knowledge!

            if($module == 'Products'){
                $query = 'SELECT label, crmid, setype, createdtime FROM vtiger_crmentity INNER JOIN vtiger_products ON
                            vtiger_products.productid = vtiger_crmentity.crmid WHERE label LIKE ? AND vtiger_crmentity.deleted = 0
                            AND vtiger_products.discontinued = 1 AND setype = ?';
            }else if($module == 'Services'){
                $query = 'SELECT label, crmid, setype, createdtime FROM vtiger_crmentity INNER JOIN vtiger_service ON
                            vtiger_service.serviceid = vtiger_crmentity.crmid WHERE label LIKE ? AND vtiger_crmentity.deleted = 0
                            AND vtiger_service.discontinued = 1 AND setype = ?';
            }

Customize this queries, like you need.

If you will query a custom fields (in this example cf_645), you need to modify the code in this way:

if($module == 'Products'){
    $query = 'SELECT label, crmid, setype, createdtime FROM vtiger_crmentity
                INNER JOIN vtiger_products ON  vtiger_products.productid = vtiger_crmentity.crmid
                INNER JOIN vtiger_productcf ON vtiger_products.productid = vtiger_productcf.productid
                          WHERE (label LIKE ? OR cf_645 LIKE ?) AND vtiger_crmentity.deleted = 0
                AND vtiger_products.discontinued = 1 AND setype = ?';
    $params[] = "%$searchKey%";
}else if($module == 'Services'){
    $query = 'SELECT label, crmid, setype, createdtime FROM vtiger_crmentity INNER JOIN vtiger_service ON
                vtiger_service.serviceid = vtiger_crmentity.crmid WHERE label LIKE ? AND vtiger_crmentity.deleted = 0
                AND vtiger_service.discontinued = 1 AND setype = ?';
}