【译】第40节---EF6-命令监听

原文：http://www.entityframeworktutorial.net/entityframework6/database-command-interception.aspx

本节，将学习如何在执行数据库命令时拦截EF。

EF 6提供了在对数据库执行ExecuteNonQuery，ExecuteScalar，ExecuteReader操作之前和之后使用IDbCommandInterceptor拦截上下文的能力。

首先，实现IDbCommandInterceptor，如下所示：

class EFCommandInterceptor: IDbCommandInterceptor
{
    public void NonQueryExecuted(System.Data.Common.DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
    {
        LogInfo("NonQueryExecuted", String.Format(" IsAsync: {0}, Command Text: {1}", interceptionContext.IsAsync, command.CommandText));
    }
 
    public void NonQueryExecuting(System.Data.Common.DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
    {
        LogInfo("NonQueryExecuting", String.Format(" IsAsync: {0}, Command Text: {1}", interceptionContext.IsAsync,  command.CommandText));
    }
 
    public void ReaderExecuted(System.Data.Common.DbCommand command, DbCommandInterceptionContextt<System.Data.Common.DbDataReader> interceptionContext)
    {
        LogInfo("ReaderExecuted", String.Format(" IsAsync: {0}, Command Text: {1}", interceptionContext.IsAsync, command.CommandText));
    }
 
    public void ReaderExecuting(System.Data.Common.DbCommand command, DbCommandInterceptionContext<System.Data.Common.DbDataReader> interceptionContext)
    {
        LogInfo("ReaderExecuting", String.Format(" IsAsync: {0}, Command Text: {1}", interceptionContext.IsAsync, command.CommandText));
    }
 
    public void ScalarExecuted(System.Data.Common.DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
        LogInfo("ScalarExecuted", String.Format(" IsAsync: {0}, Command Text: {1}", interceptionContext.IsAsync, command.CommandText));
    }
 
    public void ScalarExecuting(System.Data.Common.DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
        LogInfo("ScalarExecuting", String.Format(" IsAsync: {0}, Command Text: {1}", interceptionContext.IsAsync, command.CommandText));
    }
 
    private void LogInfo(string command, string commandText)
    {
        Console.WriteLine("Intercepted on: {0} :- {1} ", command, commandText);
    }
}

可以在上面的代码中看到，IDbCommandInterceptor提供了六种执行方法。

现在，需要使用配置文件或基于代码的配置来配置拦截器。

配置文件：

<entityFramework>
    <interceptors>
        <interceptor type="EF6DBFirstTutorials.EFCommandInterceptor, EF6DBFirstTutorials">
        </interceptor>
    </interceptors>
</entityFramework>

基于代码配置：

public class FE6CodeConfig : DbConfiguration
    {
        public FE6CodeConfig()
        {
            this.AddInterceptor(new EFCommandInterceptor());
        }
    }

所以现在我们可以在DbContext执行ExecuteNonQuery，ExecuteScalar和ExecuteReader时记录命令。