关于是用LINQ to SQL模拟并发冲突的问题

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data.Linq;



namespace Demo03Ex01

{

    class Program

    {

        static void Main(string[] args)

        {

            NorthwindDataContext dbUserA = new NorthwindDataContext(@"C:\LINQ\Northwind.mdf");

            NorthwindDataContext dbUserB = new NorthwindDataContext(@"C:\LINQ\Northwind.mdf");



            StreamWriter UserAWriter = File.CreateText(@"C:\LINQ\UserA.log");

            dbUserA.Log = UserAWriter;



            StreamWriter UserBWriter = File.CreateText(@"C:\LINQ\UserB.log");

            dbUserB.Log = UserBWriter;



            try

            {

                // 用户A和用户B同时获取相同的记录。

                var UserACustomers = dbUserA.Customers.Skip(30).Take(7).ToList();

                var UserBCustomers = dbUserB.Customers.Skip(30).Take(7).ToList();



                // 用户B首先修改数据并更新到数据。

                foreach (var CustomerObject in UserBCustomers)

                {

                    CustomerObject.ContactName = "UserB";

                    CustomerObject.ContactTitle = "UserB";

                    CustomerObject.Country = "UserB";

                    CustomerObject.City = "UserB";

                    CustomerObject.Address = "UserB";

                }

                dbUserB.SubmitChanges();



                // 然后才是用户A修改数据，并尝试更新到数据库，此时将引发并发冲突。

                foreach (var CustomerObject in UserACustomers)

                {

                    CustomerObject.ContactName = "UserA";

                    CustomerObject.ContactTitle = "UserA";

                    CustomerObject.Country = "UserA";

                    CustomerObject.City = "UserA";

                    CustomerObject.Address = "UserA";

                }

                dbUserA.SubmitChanges(ConflictMode.FailOnFirstConflict);

            }

            catch (ChangeConflictException ex)

            {

                Console.WriteLine(ex.Message);

                Console.WriteLine();

                Console.WriteLine("Change Conflict Objects Count : {0}",

                    dbUserA.ChangeConflicts.Count);

            }

            

            UserAWriter.Close();

            UserBWriter.Close();

        }

    }

}