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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] = @1 WHERE ((([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 TimeStamp 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。
数据注解特性之ConcurrencyCheck特性【Code-First系列】
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原文地址：http://www.cnblogs.com/caofangsheng/p/5023802.html
