EF架构~通过EF6的DbCommand拦截器来实现数据库读写分离

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前几天看了一个基于sqlserver的负载均衡与读写分离的软件Moebius,实现的方式还是不错的，这使得用sqlserver数据库的同学时有机会对数据库进行更有效的优化了

看着人有做的东西，自己也想用ＥＦ来实现一个读写分离，所以就有了本篇文章，仓储大叔读写分离的思路是：

1　　用sqlserver自带的发布、订阅实现主，从数据库的结构，同步这事由sql帮我们完成

2　　配置文件建立几个供只读的数据库连接串

3　　建立ＳＱＬ命令拦截器

4　　修改大叔的DbContextRepository基数，添加拦截行为

5　　测试，搞定

有了上面的想法，咱就可以干事了，第一步不用说了，可以自己百度，从第２步说起

2　　配置文件建立几个供只读的数据库连接串

    <!-- 只写-->

    <add name="backgroundEntities" connectionString="metadata=res://*/background.csdl|res://*/background.ssdl|res://*/background.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=.;initial catalog=background;persist security info=True;user id=sa;password=zzl123;multipleactiveresultsets=True;application name=EntityFramework&quot;" providerName="System.Data.EntityClient" />

    <!-- 只读-->

    <add name="backgroundEntitiesRead" connectionString="metadata=res://*/background.csdl|res://*/background.ssdl|res://*/background.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=.;initial catalog=background_Read1;persist security info=True;user id=sa;password=zzl123;multipleactiveresultsets=True;application name=EntityFramework&quot;" providerName="System.Data.EntityClient" />

3　　建立ＳＱＬ命令拦截器

 /// <summary>

    /// SQL命令拦截器

    /// </summary>

    public class NoLockInterceptor : DbCommandInterceptor

    {

        private static readonly Regex _tableAliasRegex =

            new Regex(@"(?<tableAlias>AS \[Extent\d+\](?! WITH \(NOLOCK\)))",

                RegexOptions.Multiline | RegexOptions.IgnoreCase);



        [ThreadStatic]

        public static bool SuppressNoLock;

        public override void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)

        {

            string conn = command.Connection.ConnectionString;

            base.NonQueryExecuting(command, interceptionContext);

        }

        public override void ScalarExecuting(DbCommand command,

            DbCommandInterceptionContext<object> interceptionContext)

        {

            command.Connection.Close();

            command.Connection.ConnectionString = "data source=.;initial catalog=background_Read1;persist security info=True;user id=sa;password=zzl123;multipleactiveresultsets=True;application name=EntityFramework";

            command.Connection.Open();



            if (!SuppressNoLock)

            {

                command.CommandText =

                    _tableAliasRegex.Replace(command.CommandText, "${tableAlias} WITH (NOLOCK)");

            }

        }



        public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)

        {

            command.Connection.Close();

            command.Connection.ConnectionString = "data source=.;initial catalog=background_Read1;persist security info=True;user id=sa;password=zzl123;multipleactiveresultsets=True;application name=EntityFramework";

            command.Connection.Open();

            if (!SuppressNoLock)

            {

                command.CommandText =

                    _tableAliasRegex.Replace(command.CommandText, "${tableAlias} WITH (NOLOCK)");

            }

        }

    }

4　　修改大叔的DbContextRepository基数，添加拦截行为

  public DbContextRepository(IUnitOfWork db, Action<string> logger)

        {

            UnitWork = db;

            Db = (DbContext)db;

            Logger = logger;

            ((IObjectContextAdapter)Db).ObjectContext.CommandTimeout = 0;



            //SQL语句拦截器

            System.Data.Entity.Infrastructure.Interception.DbInterception.Add(new EntityFrameworks.Data.Core.Common.NoLockInterceptor());

            EntityFrameworks.Data.Core.Common.NoLockInterceptor.SuppressNoLock = true;

        }

5　　大功造成，感谢阅读！

本文章代码没有全部展示，只是展示一种思想，希望可以给大家带来帮助。

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