EF 6 DB-First系列--在Entity Framework中拦截数据库命令

在Entity Framework中拦截数据库命令

在这里，您将学习如何拦截EF 6中DbContext执行的数据库命令。

EF 6通过实现IDbCommandInterceptor接口提供了拦截上下文的能力。IDbCommandInterceptor接口包括一些方法，这些方法可以拦截DbContext的实例，并允许你在上下文执行命令或查询之前或之后执行你的自定义逻辑。DbContext使用ADO.NET中的方法执行命令和查询，如ExecuteNonQuery, ExecuteScalar和ExecuteReader，您可以通过实现NonQueryExecuted和NonQueryExecuting等方法来拦截它们。

要拦截DbContext的一个实例，首先，创建自定义类并实现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, DbCommandInterceptionContext<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);
    }
}

在上面的示例中可以看到，IDbCommandInterceptor提供了六个实现方法。它记录命令以供演示，但您可以在这里编写自定义逻辑。

接下来，您需要使用配置文件或基于代码的配置来配置拦截器。

在app.config文件中配置拦截器，如下所示:

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

如果使用基于代码的配置，则按如下所示配置。

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

所以现在，当实例DbContext执行命令或查询时，我们可以记录命令。考虑下面的例子。

var newStudent =  new Student() { FirstName = "Bill" };

using (var context = new SchoolDBEntities())
{
    context.Students.Add(newStudent);
    context.SaveChanges();
}

上面的示例将记录以下内容。

Output:

Intercepted on: ReaderExecuting :- IsAsync: False, Command Text: INSERT [dbo].[Student]([FirstName], [StandardId], [LastName])
VALUES (@0, NULL, NULL)
SELECT [StudentID], [RowVersion] FROM [dbo].[Student]
WHERE @@ROWCOUNT > 0 AND [StudentID] = scope_identity()
Intercepted on: ReaderExecuted :- IsAsync: False, Command Text: INSERT [dbo].[Student]([FirstName], [StandardId], [LastName])
VALUES (@0, NULL, NULL)
SELECT [StudentID], [RowVersion] FROM [dbo].[Student]
WHERE @@ROWCOUNT > 0 AND [StudentID] = scope_identity()

参考

https://www.entityframeworktutorial.net/
https://msdn.microsoft.com/