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EF中的开放式并发（EF基础系列）

好久没更新EF这个系列了，现在又重新开始。

这次学习，开放式并发。首先拿出数据库脚本：

说明一下，这个数据库脚本是之前的章节中稍作修改的：

USE [SchoolDB] GO /****** Object:  Table [dbo].[Student] Script Date: 11/30/2015 21:42:07 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[Student](  [StudentID] [INT] NOT NULL,  [StudentName] [NVARCHAR](100) NULL,  [StandardID] [INT] NULL,  [RowVersion] [TIMESTAMP] NOT NULL,  CONSTRAINT [PK__Student__32C52A7903317E3D] PRIMARY KEY CLUSTERED  (  [StudentID] ASC )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY] ) ON [PRIMARY] GO ALTER TABLE [dbo].[Student]  WITH CHECK ADD  CONSTRAINT [FK__Student__Standar__0519C6AF] FOREIGN KEY([StandardID]) REFERENCES [dbo].[Standard] ([StandardID]) GO ALTER TABLE [dbo].[Student] CHECK CONSTRAINT [FK__Student__Standar__0519C6AF] GO

然后，我们在数据模型中更新一下模型EDMx

EF中的开放式并发（EF基础系列）

可以看到Student模型上面，出现了Rowversion字段，我们选中它，右键-->属性，修改并发模式为Fixed。

EF中的开放式并发（EF基础系列）

EF will now include a RowVersion column in the where clause, whenever you do an update operation and if the rowversion value is different than in the where clause then it will throw DbUpdateConcurrencyExection .

下面开始实践：

using System; using System.Collections.Generic; using System.Data.Entity; using System.Data.Entity.Core.Objects; using System.Data.Entity.Infrastructure; using System.Linq; using System.Text; using System.Threading.Tasks; namespace EFTutorials {  class Program  {   static void Main(string[] args)   {    Student stu1 = null;    Student stu2 = null;    using (var db = new SchoolDBEntities1())    {     db.Configuration.ProxyCreationEnabled = false;     stu1 = db.Students.Where(s => s.StudentID == 1).FirstOrDefault();    }    using (var db = new SchoolDBEntities1())    {     db.Configuration.ProxyCreationEnabled = false;     stu2 = db.Students.Where(s => s.StudentID == 1).FirstOrDefault();    }    stu1.StudentName = "Edit Stuent1";    stu2.StudentName = "Edit Stuent2";    using (var db = new SchoolDBEntities1())    {     try     {      db.Entry(stu1).State = EntityState.Modified;      db.SaveChanges();     }     catch (DbUpdateConcurrencyException ex)     {      Console.WriteLine("Optimistic Concurrency exception occured");     }    }    using (var db = new SchoolDBEntities1())    {     try     {      db.Entry(stu2).State = EntityState.Modified;      db.SaveChanges();     }     catch (DbUpdateConcurrencyException ex)     {      Console.WriteLine("Optimistic Concurrency exception occured");     }    }   }  } }

执行完stu1那个查询之后：

SELECT TOP (1)

[Extent1].[StudentID] AS [StudentID],

[Extent1].[StudentName] AS [StudentName],

[Extent1].[StandardID] AS [StandardID],

[Extent1].[RowVersion] AS [RowVersion]

FROM [dbo].[Student] AS [Extent1]

WHERE 1 = [Extent1].[StudentID]

执行完，stu1的保存修改之后：

exec sp_executesql N'UPDATE [dbo].[Student]

SET [StudentName] = @0, [StandardID] = NULL

WHERE (([StudentID] = @1) AND ([RowVersion] = @2))