给 EF Core 查询增加 With NoLock

给 EF Core 查询增加 With NoLock

Intro

EF Core 在 3.x 版本中增加了 Interceptor,使得我们可以在发生低级别数据库操作时作为 EF Core 正常运行的一部分自动调用它们。 例如,打开连接、提交事务或执行命令时。

所以我们可以自定义一个 Interceptor 来记录执行的 sql 语句,也可以通过 Interceptor 来实现 sql 语句的执行。

这里我们可以借助 Interceptor 实现对于查询语句的修改,自动给查询语句加 (WITH NOLOCK)WITH NOLOCK 等效于 READ UNCOMMITED(读未提交)的事务级别,这样会造成一定的脏读,但是从效率上而言,是比较高效的,不会因为别的事务长时间未提交导致查询阻塞,所以对于大数据场景下,查询 SQL 加 NOLOCK 还是比较有意义的

NoLockInterceptor

继承 DbCommandInterceptor,重写查询 sql 执行之前的操作,在执行 sql 之前增加 WITH(NOLOCK),实现代码如下:

public class QueryWithNoLockDbCommandInterceptor : DbCommandInterceptor  {      private static readonly Regex TableAliasRegex =          new Regex(@"(?<tableAlias>AS [[a-zA-Z]w*](?! WITH (NOLOCK)))",              RegexOptions.Multiline | RegexOptions.Compiled | RegexOptions.IgnoreCase);        public override InterceptionResult<object> ScalarExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<object> result)      {          command.CommandText = TableAliasRegex.Replace(              command.CommandText,              "${tableAlias} WITH (NOLOCK)"              );          return base.ScalarExecuting(command, eventData, result);      }        public override Task<InterceptionResult<object>> ScalarExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<object> result,          CancellationToken cancellationToken = new CancellationToken())      {          command.CommandText = TableAliasRegex.Replace(              command.CommandText,              "${tableAlias} WITH (NOLOCK)"              );          return base.ScalarExecutingAsync(command, eventData, result, cancellationToken);      }        public override InterceptionResult<DbDataReader> ReaderExecuting(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result)      {          command.CommandText = TableAliasRegex.Replace(              command.CommandText,              "${tableAlias} WITH (NOLOCK)"              );          return result;      }        public override Task<InterceptionResult<DbDataReader>> ReaderExecutingAsync(DbCommand command, CommandEventData eventData, InterceptionResult<DbDataReader> result,          CancellationToken cancellationToken = new CancellationToken())      {          command.CommandText = TableAliasRegex.Replace(              command.CommandText,              "${tableAlias} WITH (NOLOCK)"              );          return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);      }  }  

Interceptor 的使用

在注册 DbContext 服务的时候,可以配置 Interceptor,配置如下:

var services = new ServiceCollection();  services.AddDbContext<TestDbContext>(options =>  {      options          .UseLoggerFactory(loggerFactory)          .UseSqlServer(DbConnectionString)          .AddInterceptors(new QueryWithNoLockDbCommandInterceptor())          ;  });  

使用效果

通过 loggerFactory 记录的日志查看查询执行的 sql 语句

可以看到查询语句自动加上了 WITH (NOLOCK)

Reference