@RestResource(urlMapping='/QlmOrderRESTApi/*')
global with sharing class QlmOrderController{

    @HttpPost
    global static String doPost(String orderNumber) {
        String orderXML = '';
        
        List<Order> orderList = [select id, OrderNumber , BillToContactId, BillToContact.Name, BillToContact.Email,
                                 BillToContact.MailingStreet, BillToContact.MailingCity, BillToContact.MailingState, BillToContact.MailingPostalCode,
                                 BillToContact.MailingCountry, 
                                (select id, Quantity, Product2.Name, Product2.ProductCode from OrderItems)
                                 from Order where OrderNumber =: orderNumber];
        
        if(orderList.size() > 0)
        {
            orderXML += '<Order>';
                orderXML += '<OrderId>'       + orderList[0].Id                  + '</OrderId>';
                orderXML += '<OrderNumber>'   + orderList[0].OrderNumber         + '</OrderNumber>';
                orderXML += '<CustomerId>'    + orderList[0].BillToContactId     + '</CustomerId>';
                orderXML += '<CustomerName>'  + orderList[0].BillToContact.Name  + '</CustomerName>';
                orderXML += '<CustomerEmail>' + orderList[0].BillToContact.Email + '</CustomerEmail>';
                orderXML += '<MailingStreet>' + orderList[0].BillToContact.MailingStreet + '</MailingStreet>';
                orderXML += '<MailingCity>'   + orderList[0].BillToContact.MailingCity + '</MailingCity>';
                orderXML += '<MailingState>'  + orderList[0].BillToContact.MailingState + '</MailingState>';
                orderXML += '<MailingPostalCode>' + orderList[0].BillToContact.MailingPostalCode + '</MailingPostalCode>';
                orderXML += '<MailingCountry>' + orderList[0].BillToContact.MailingCountry + '</MailingCountry>';
                
                orderXML += '<OrderItems>';
                    
                    for(OrderItem oi : orderList[0].OrderItems)
                    {
                        orderXML += '<OrderItem>';
                        
                            orderXML += '<ProductName>' + oi.Product2.Name + '</ProductName>';
                            orderXML += '<ProductCode>' + oi.Product2.ProductCode + '</ProductCode>';
                            orderXML += '<Quantity>' + oi.Quantity + '</Quantity>';
                        
                        orderXML += '</OrderItem>';
                    }
                    
                orderXML += '</OrderItems>';
            orderXML += '</Order>';
        }
        else
        {
            orderXML = '<Message>Order not found with order number ' + orderNumber + '</Message>';
        }
        
        return orderXML;
    }
}