how to get root node attribute value using linq

first, fix your xml (<Order .... />) then, your linq should look like this....

// .Elements(...) selects all elements of type "Customer"
    var q = from c in xDoc.Elements("Customers") 
    select new
    {
        dID = c.Attribute("dId"), 
        dTime = c.Attribute("dTime")
    }; 

you should dl LinqPad... it lets you do Linq queries on the fly, even agains SQL databases. Then, once you get the results you want, copy and past your linq into your source code.

You have to end the order tag with: />

xDoc.Descendants("Customers") should work as well as xDoc.Elements("Customers").

Chris, is there a specific advantage to using .Elements?

You can't use LINQ to access the root tag. The code below does what you want (I included a well formed xml file as well):

using System;
using System.Linq;
using System.Xml.Linq;

namespace ReadXmlSpike
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Reading file...");
            XDocument doc = XDocument.Load("Customers.xml");
            var customers =
                new
                    {
                        DID = (string) doc.Element("Customers").Attribute("did"),
                        DTime = (DateTime) doc.Element("Customers").Attribute("dTime"),
                        Customers = from customerxml in doc.Descendants("Customer")
                                    select
                                        new
                                            {
                                                ID = (string)customerxml.Attribute("id"),
                                                Orders = from orderxml in customerxml.Descendants("Order")
                                                         select
                                                             new
                                                                 {
                                                                     Number =(string) orderxml.Attribute("number")
                                                                 }
                                            }
                    };
            Console.WriteLine("Customersfile with id: {0} and time {1}",customers.DID,customers.DTime);
            foreach (var customer in customers.Customers)
            {
                Console.WriteLine("Customer with id {0} has the following orders:",customer.ID);
                foreach (var order in customer.Orders)
                {
                    Console.WriteLine("Order with number {0}",order.Number);
                }
            }
            Console.ReadLine();
        }
    }
}

and the xml file:

<?xml version="1.0" encoding="utf-8" ?>
<Customers did="www" dTime="10-09-09 11:23">
  <Customer id="1">
    <Orders>
      <Order number="22" status="ok"/>
      <Order number="23" status="bad"/>
    </Orders>
  </Customer>
  <Customer id="2">
    <Orders>
      <Order number="24" status="ok"/>
      <Order number="25" status="bad"/>
    </Orders>
  </Customer>
</Customers>

    XDocument d = XDocument.Parse(@"<?xml version='1.0' encoding='utf-8' ?>
        <Customers dId='wqwx' dTime='10-9-09 11:23'>
            <Customer id='1'>      
                <Orders>        
                    <Order number='22' status='ok'/>      
                </Orders>   
            </Customer> 
        </Customers>");
    var cu = d.Root.Elements().Where(n => n.Name == "Customer");


    var c = from cc in cu
            select new
            {
                dId = cc.Document.Root.Attribute("dId").Value,
                dTime = cc.Document.Root.Attribute("dTime").Value,
                ID = cc.Attribute("id").Value,
                number = cc.Element("Orders").Element("Order").Attribute("number").Value
            };

    foreach (var v in c)
    {
        Console.WriteLine("dId \t\t= {0}", v.dId);
        Console.WriteLine("dTime \t\t= {0}", v.dTime);
        Console.WriteLine("CustomerID \t= {0}", v.ID);
        Console.WriteLine("OrderCount \t= {0}", v.number);
    }

Console Output:
================================
dId = wqwx
dTime = 10-9-09 11:23
CustomerID = 1
OrderCount = 22
请按任意键继续. . .

It does not work the way you wrote it: while printing the above code would complain about anonymous type.

However, with this simple modified version d.Document.Root.Attribute("dId").Value; you can assign it to a string.