ConcurrencyCheck特性可以应用到领域类的属性中。当EF执行更新操作的时候，Code-First将列的值放在where条件语句中，你可以使用这个CurrencyCheck特性，使用已经存在的列做并发检查，而不是使用单独的TimeStamp列来做并发检查。

看下面的代码：

using System;using System.Collections.Generic;using System.ComponentModel.DataAnnotations;using System.ComponentModel.DataAnnotations.Schema;using System.Linq;using System.Text;using System.Threading.Tasks;namespace EF2{    [Table("StudentInfo")]   public class Student    {        [Key]        [Column(Order=1)]        public int StudentKey1 { get; set; }        [Key]        [Column(Order=2)]        public int StudentKey2 { get; set; }        [Column("Name",TypeName="ntext")]        [MaxLength(20)]        [ConcurrencyCheck]        public string StudentName { get; set; }        [NotMapped()]        public int? Age { get; set; }        public int StdId { get; set; }        [ForeignKey("StdId")]        public virtual Standard Standard { get; set; }        [Timestamp]        public byte[] RowVersion { get; set; }    }}

然后我们来修改一下Main函数测试的代码：

using System;using System.Collections.Generic;using System.Data.Entity;using System.Data.Entity.Infrastructure;using System.Linq;using System.Text;using System.Threading.Tasks;namespace EF2{    class Program    {        static void Main(string[] args)        {            Student stuModel1 = null;            Student stuModel2 = null;                using (var db = new DbContextClass())                {                    stuModel1 = db.Students.Where(s => s.StudentKey1 == 1 && s.StudentKey2 == 1).Single();                }                using (var db = new DbContextClass())                {                    stuModel2 = db.Students.Where(s => s.StudentKey1 == 1 && s.StudentKey2 == 1).Single();                }                stuModel1.StudentName = "Test Only For one";                stuModel2.StudentName = "Test Only For twos";                try                {                    using (var db = new DbContextClass())                    {                        db.Entry(stuModel1).State = EntityState.Modified;                        db.SaveChanges();                    }                }                catch (DbUpdateConcurrencyException ex)                {                    Console.WriteLine(ex.Message);                }                try                {                    using (var db = new DbContextClass())                    {                        db.Entry(stuModel2).State = EntityState.Modified;                        db.SaveChanges();                    }                }                catch (DbUpdateConcurrencyException ex)                {                    Console.WriteLine(ex.Message);                }            Console.ReadKey();        }    }}

然后错误并发消息是：

 

exec sp_executesql N'UPDATE [dbo].[StudentInfo]SET [StudentName] = @0, [StdId] = @1WHERE ((([StudentKey1] = @2) AND ([StudentKey2] = @3)) AND ([StudentName] = @4))',N'@0 nvarchar(20),@1 int,@2 int,@3 int,@4 nvarchar(20)',@0=N'Test Only For one',@1=1,@2=1,@3=1,@4=N'Test Only For one'

请注意：

Note that  attribute can only be applied to a single byte array property in a class, whereas ConcurrencyCheck attribute can be applied to any number of properties with any datatype.

TimeStamp特性只能够被用到单字节属性的类中，但是ConcurrencyCheck特性可以被用到任何数量，任何类型的属性中。