How to fetch product line item in order module. ?

How to fetch product line item in order module. ?

Hi Team,

      I have a issue in Zoho CRM. How to fetch a product line items ( quantity field ) in  Sales Order module ? For that i have written the below code but it shows error. Please check it and let me know. I am attaching the error also.

Code :

void test(int order_id)
{
respMap = zoho.crm.getRecordById("SalesOrders",order_id);
productDet = ifnull(respMap.get("product"),"");
info productDet;
qty = ifnull(productDet.get("Quantity"),"0.0").toDecimal();
info qty;
}

Waiting for your reply.Hope will get a response ASAP.