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=)]
public int StudentKey1 { get; set; }
[Key]
[Column(Order=)]
public int StudentKey2 { get; set; }
[Column("Name",TypeName="ntext")]
[MaxLength()]
[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 == && s.StudentKey2 == ).Single();
}
using (var db = new DbContextClass())
{
stuModel2 = db.Students.Where(s => s.StudentKey1 == && s.StudentKey2 == ).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] = @, [StdId] = @ WHERE ((([StudentKey1] = @) AND ([StudentKey2] = @)) AND ([StudentName] = @)) nvarchar(),@ nvarchar()',@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。