利用LINQ 表达式实现跨服务器查询

using System;
using System.Collections.Generic;
using System.Data.Linq;
using System.Data.Linq.Mapping;
using System.Linq;

namespace LinqConsoleApp
{
    //参考：http://msdn.microsoft.com/en-us/bb534644%28zh-cn%29.aspx
    class App
    {
        static void Main(string[] args)
        {
            //建立不同的服务器连接
            DataContext cdb = new DataContext(@"server=*****;database=Northwind;uid=sa;pwd=ll");
            Table<Customer> customer = cdb.GetTable<Customer>();

            DataContext odb = new DataContext(@"server=*****;database=Test;uid=sa;pwd=ll");
            Table<Order> order = odb.GetTable<Order>();

            //查询表达式
            IQueryable<Customer> cq = from c in customer
                            where c.City == "Berlin"
                            select c;

            IQueryable<Order> oq = from o in order
                            where o.OrderDate >DateTime.Parse("1997-10-03")
                            select o;


            //转换类型，如果用IQueryable<T>的Join方法连接对出现<查询包含对不同数据上下文上所定义项的引用>错误。
            List<Customer> cl = cq.ToList<Customer>();
            List<Order> ol = oq.ToList<Order>(); 


            //建立对应关系
            var join = cl.Join(ol,
                c => c.CustomerID,
                o => o.CustomerID,
                (c,o) => new 
                    {
                        CustomerID = c.CustomerID,
                        City = c.City,

                        Orders = o.OrderID,
                        OrderDate = o.OrderDate
                    });

            try
            {
                foreach (var j in join)
                {
                    Console.WriteLine("CustomerID={0},City={1}, Orders={2},OrderDate={3}", 
                    j.CustomerID, j.City, j.Orders,j.OrderDate);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message + "\r\n" + ex.StackTrace);
            }
            Console.ReadLine();
        }
    }

    //建立实体类Customers
    [Table(Name = "Customers")]
    public class Customer
    {
        [Column]
        public string CustomerID
        {
            get;
            set;
        }

        [Column]
        public string City
        {
            get;
            set;
        }
    }

    //建立实体类Orders
    [Table(Name = "Orders")]
    public class Order
    {
        [Column]
        public int OrderID
        {
            get;
            set;
        }

        [Column]
        public string CustomerID
        {
            get;
            set;
        }

        [Column]
        public DateTime OrderDate
        {
            get;
            set;
        }
    }
}