前言

本文主要是讲解EF Core3.0+ 通过拦截器实现读写分离与SQL日志记录

注意拦截器只有EF Core3.0+ 支持,2.1请考虑上下文工厂的形式实现.

说点题外话..

一晃又大半年没更新技术博客..唉,去年一年发生了太多事情..博主真的一言难尽..

有兴趣的可以去看看:记录一下,也许是转折,也许是结束,也许是新希望的一年

正文

1.通过拦截器实现读写分离

先讲一下本文实现的方式吧

SQL 通过数据库本身的功能实现主从备份大概原理如图:

EF Core在查询的时候通过DbCommandInterceptor 拦截器(PS:这个功能在EF6.0+中也实现了)来拦截对数据库的访问,从而切换主从数据库

下面直接上代码吧

首先我们创建一个类继承DbCommandInterceptor:

public class DbMasterSlaveCommandInterceptor : DbCommandInterceptor

    {private string _masterConnectionString;private string _slaveConnectionString;public DbMasterSlaveCommandInterceptor(string masterConnectionString, string slaveConnectionString){_masterConnectionString = masterConnectionString;_slaveConnectionString = slaveConnectionString;}
}

通过构造函数传递主库连接地址与从库地址(可有多个通过"|"分割)

添加一个随机分配从表读取连接的方法(PS:这里只是demo所以很简陋的随机,如果正式要用,应包含权重判断,定时心跳从库连接情况,请自行修改):

　　　　/// <summary>

        /// 通过随机数分配获取多个从库/// </summary>/// <returns></returns>private string GetSlaveConnectionString(){var readArr = _slaveConnectionString.Split(new char[] { '|' }, StringSplitOptions.RemoveEmptyEntries);var resultConn = string.Empty;if (readArr != null && readArr.Any()){resultConn = readArr[Convert.ToInt32(Math.Floor((double)new Random().Next(0, readArr.Length)))];}return resultConn;}

添加判断是否主从操作连接方法:

private void UpdateToSlave(DbCommand command)

        {//判断是否配置了主从分离if (!string.IsNullOrWhiteSpace(GetSlaveConnectionString()))//如果配置了读写分离，就进入判断{//判断是否为插入语句(EF 插入语句会通过Reader执行并查询主键),否则进入if (command.CommandText.ToLower().StartsWith("insert", StringComparison.InvariantCultureIgnoreCase) == false){// 判断当前会话是否处于分布式事务中bool isDistributedTran = Transaction.Current != null &&Transaction.Current.TransactionInformation.Status !=TransactionStatus.Committed;//判断该 context 是否处于普通数据库事务中bool isDbTran = command.Transaction != null;//如果不处于事务中,则执行从服务器查询if (!isDbTran && !isDistributedTran){command.Connection.Close();command.Connection.ConnectionString = GetSlaveConnectionString();command.Connection.Open();}}}}

重载DbCommandInterceptor当中的拦截方法,代码如下:

        //如果是写入,则正常执行public override InterceptionResult<int> NonQueryExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<int> result){return base.NonQueryExecuting(command, eventData, result);}public override Task<InterceptionResult<int>> NonQueryExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<int> result, CancellationToken cancellationToken = default){return base.NonQueryExecutingAsync(command, eventData, result, cancellationToken);}public override InterceptionResult<DbDataReader> ReaderExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result){this.UpdateToSlave(command);return base.ReaderExecuting(command, eventData, result);}public override Task<InterceptionResult<DbDataReader>> ReaderExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result, CancellationToken cancellationToken = default){this.UpdateToSlave(command);return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);}public override InterceptionResult<object> ScalarExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<object> result){this.UpdateToSlave(command);return base.ScalarExecuting(command, eventData, result);}public override Task<InterceptionResult<object>> ScalarExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<object> result, CancellationToken cancellationToken = default){this.UpdateToSlave(command);return base.ScalarExecutingAsync(command, eventData, result, cancellationToken);}

最后在EF core的上下文中注入拦截器(PS:我这里使用的Autofac模块注入):

                builder.Register(c =>{var optionsBuilder = new DbContextOptionsBuilder<TestEFContext>();//注入拦截器optionsBuilder.AddInterceptors(new DbMasterSlaveCommandInterceptor(WriteConnect, ReadConnect));//MaxBatchSize 处理批量操作BUGoptionsBuilder.UseMysql(WriteConnect, b=>b.MaxBatchSize(1));return optionsBuilder.Options;}).As<DbContextOptions<TestEFContex>>().SingleInstance();

这样就实现了通过拦截器实现读写分离.

2.通过拦截器实现SQL日志记录

同理,我们可以通过拦截器实现EF Core SQL语句的记录与调试

首先我们创建一个新的拦截器DBlogCommandInterceptor 如下:

public class DBlogCommandInterceptor : DbCommandInterceptor{//创建一个队列记录SQL执行时间static readonly ConcurrentDictionary<DbCommand, DateTime> MStartTime = new ConcurrentDictionary<DbCommand, DateTime>();private ILogger<DBlogCommandInterceptor> _logger { get; set; }//通过构造函数注入日志public DBlogCommandInterceptor(ILogger<DBlogCommandInterceptor> Logger){_logger = Logger;}
}

创建2个私有的方法,一个记录执行开始时间,一个记录SQL

　　　　　　//记录SQL开始执行的时间 private void OnStart(DbCommand command){MStartTime.TryAdd(command, DateTime.Now);}//通过_logger输出日志private void Log(DbCommand command){DateTime startTime;TimeSpan duration;//得到此command的开始时间MStartTime.TryRemove(command, out startTime);if (startTime != default(DateTime)){duration = DateTime.Now - startTime;}else{duration = TimeSpan.Zero;}var parameters = new StringBuilder();//循环获取执行语句的参数值foreach (DbParameter param in command.Parameters){parameters.AppendLine(param.ParameterName + " " + param.DbType + " = " + param.Value);}_logger.LogInformation("{starttime}开始执行SQL语句:{sql},参数:{canshu},执行时间{readtime}",startTime.ToString(), command.CommandText, parameters.ToString(), duration.TotalSeconds);}

最后重载拦截器的方法:

public override InterceptionResult<int> NonQueryExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<int> result){OnStart(command);return base.NonQueryExecuting(command, eventData, result);}public override Task<InterceptionResult<int>> NonQueryExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<int> result, CancellationToken cancellationToken = default){OnStart(command);return base.NonQueryExecutingAsync(command, eventData, result, cancellationToken);}public override int NonQueryExecuted(DbCommand command, CommandExecutedEventData eventData, int result){Log(command);return base.NonQueryExecuted(command, eventData, result);}public override Task<int> NonQueryExecutedAsync(DbCommand command, CommandExecutedEventData eventData, int result, CancellationToken cancellationToken = default){Log(command);return base.NonQueryExecutedAsync(command, eventData, result, cancellationToken);}public override InterceptionResult<object> ScalarExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<object> result){OnStart(command);return base.ScalarExecuting(command, eventData, result);}public override Task<InterceptionResult<object>> ScalarExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<object> result, CancellationToken cancellationToken = default){OnStart(command);return base.ScalarExecutingAsync(command, eventData, result, cancellationToken);}public override object ScalarExecuted(DbCommand command, CommandExecutedEventData eventData, object result){Log(command);return base.ScalarExecuted(command, eventData, result);}public override Task<object> ScalarExecutedAsync(DbCommand command, CommandExecutedEventData eventData, object result, CancellationToken cancellationToken = default){Log(command);return base.ScalarExecutedAsync(command, eventData, result, cancellationToken);}public override InterceptionResult<DbDataReader> ReaderExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result){OnStart(command);return base.ReaderExecuting(command, eventData, result);}public override Task<InterceptionResult<DbDataReader>> ReaderExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result, CancellationToken cancellationToken = default){OnStart(command);return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);}public override Task<DbDataReader> ReaderExecutedAsync(DbCommand command, CommandExecutedEventData eventData, DbDataReader result, CancellationToken cancellationToken = default){Log(command);return base.ReaderExecutedAsync(command, eventData, result, cancellationToken);}public override DbDataReader ReaderExecuted(DbCommand command, CommandExecutedEventData eventData, DbDataReader result){Log(command);return base.ReaderExecuted(command, eventData, result);}

这样,我们就实现了通过拦截器实现SQL日志记录~效果如下: