构造正确的linq-to-xml查询时遇到问题

Question

I'm new to linq and I'm having trouble writing a query that pulls back the data I'm looking for. The xml file has orders, each order has purchase order info and products, each prouct has its own elements and descendants. I need to query all the orders and their descendants into one colletion but for some reason the linq query syntax is very counter-intuitive to me.

Here's a truncated sample of my xml

<fulfillment>
   <orders>
      <order>
         <isbulk>true</isbulk> 
         <purchaseorder>
            <id>Acme Inustries</id> 
            <quantity>15</quantity> 
         </purchaseorder>
         <items>
            <item>
               <prods>
                  <prod>
                     <seq>1</seq> 
                     <issuetype>NEW</issuetype> 
                     <loop>
                        <proxy>xyz123</proxy> 
                        <servicecode>55</servicecode> 
                     </loop>
                  </prod>
                  <prod>
                     <seq>2</seq> 
                     <issuetype>NEW</issuetype> 
                     <loop>
                        <proxy>abc987</proxy> 
                        <servicecode>121</servicecode> 
                     </loop>
                  </prod>
               </prods>
            </item>
         </items>
      </order>
      <order>
         <isbulk>true</isbulk> 
         <purchaseorder>
            <id>ABC Co</id> 
            <quantity>10</quantity> 
         </purchaseorder>
         <items>
            <item>
               <prods>
                  <prod>
                     <seq>1</seq> 
                     <issuetype>NEW</issuetype> 
                     <loop>
                        <proxy>xyz456</proxy> 
                        <servicecode>998</servicecode> 
                     </loop>
                  </prod>
                  <prod>
                     <seq>2</seq> 
                     <issuetype>NEW</issuetype> 
                     <loop>
                        <proxy>abc654</proxy> 
                        <servicecode>664</servicecode> 
                     </loop>
                  </prod>
               </prods>
            </item>
         </items>
      </order>
   </orders>
</fulfillment>

My objects look a bit like this:

public class order
{
    public bool IsBulk { get; set; }

    public PurchaseOrder PurchaseOrder = new PurchaseOrder();
    public List<prod> ListOfProds = new List<prod>();
}

public class prod
{
    public string Seq { get; set; }
    public string IssueType { get; set; }

    public string Proxy { get; set; }
    public string ServiceCode { get; set; }
}

public class PurchaseOrder
{
    public string ID { get; set; }
    public string Quantity { get; set; }
}

So I've been working on a query for the best part of a day and just can't seem to get it right. Here's what I've got so far:

List<order> orderlist = new List<order>();
XDocument xmlDoc = XDocument.Load(FilePath);

var list = (from myOrder in xmlDoc.Descendants("order")             
select new       
{
   linq_orderIsBulk = Convert.ToBoolean(myOrder.Element("isbulk").Value),

   linq_purchaseOrderID = myOrder.Element("purchaseorder").Element("id").Value,
   linq_purchaseOrderQuantity = myOrder.Element("purchaseorder").Element("quantity").Value,

   prodlist = myOrder.Element("items").Element("item").Element("prods").Elements("prod").Select(e => new
   {                
      Linq_seq = e.Element("seq").Value,
      Linq_IssueType = e.Element("issuetype").Value,

      Linq_proxy = e.Element("loop").Element("proxy").Value,
      Linq_serviceCode = e.Element("loop").Element("servicecode").Value
   }).ToList()
});

//do code to put the collection in list into List orderlist

But when I do this, I seem to end up getting an "Object reference not set to an instance of an object." error on the subquery. When I comment out the Linq_proxy and Linq_serviceCode lines, I get results but not the right ones. When I loop through list and grab a single order then look at the prodlist for that order, the count is the total amount of prods for that file (4) instead of the 2 for that order. Any thoughts?

Answer 1

I just ran this, and it works fine:

var orders = new List<order>(
    from myOrder in xmlDoc.Descendants("order")
    let purchaseOrder = myOrder.Element("purchaseorder")
    select new order {
        IsBulk = Convert.ToBoolean(myOrder.Element("isbulk").Value),
        PurchaseOrder = new PurchaseOrder {
            ID = purchaseOrder.Element("id").Value,
            Quantity = purchaseOrder.Element("quantity").Value
        },
        ListOfProds = new List<prod>(
            from product in myOrder.Descendants("prod")
            let loop = product.Element("loop")
            select new prod
            {                
                Seq = product.Element("seq").Value,
                IssueType = product.Element("issuetype").Value,
                Proxy = loop.Element("proxy").Value,
                ServiceCode = loop.Element("servicecode").Value
            }
        )
    }
);

Notice that you can project a collection directly into objects of your type, so you don't have to have code later on to create your orders collection.