Interception:

Here, you will learn how to intercept EF when it executes database commands.

EF 6 provides the ability to intercept the context using IDbCommandInterceptor before and after it performs the ExecuteNonQuery, ExecuteScalar, ExecuteReader operations to the database.

First, implement IDbCommandInterceptor as shown below:

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);
    }
}

You can see in the above code that IDbCommandInterceptor provides six methods to execute.

Now, you will need to configure the interceptor either by using config file or code-based configuration.

Config file:

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

Code-based config:

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

So now, we can log commands whenever DbContext executes ExecuteNonQuery, ExecuteScalar, and ExecuteReader.

Download DB First sample project for interception demo.