Plugin to get Order-details using QueryExpression - Microsoft Dynamics CRM

  //Setup query to get all sales order details

  QueryExpression q = new QueryExpression();
   q.EntityName = "salesorderdetail";
    ColumnSet cSet = new ColumnSet(new string[] { "salesorderdetailid", "quantity", "productid" });
     q.ColumnSet = cSet;
    ConditionExpression con1 = new ConditionExpression("salesorderid", ConditionOperator.Equal, SalesOrderID.ToString());
    FilterExpression filter = new FilterExpression();
    filter.Conditions.Add(con1);
    q.Criteria = filter;
     RetrieveMultipleRequest retrieve = new RetrieveMultipleRequest();
     retrieve.Query = q;

     //Get the response
    RetrieveMultipleResponse response = (RetrieveMultipleResponse)service.Execute(retrieve);