Using a Connection String Name with Log4Net AdoNetAppender

Log4Net is a great tool to quickly add logging to a .Net application. However one feature that has been missing is the ability to provide a connection string name in the configuration for the AdoNetAppender. Currently out of the box you have to provide the full connection string in the AdoNetAppender configuration settings. This can violate the DRY principle if the same connection string is already set up in the connectionStrings section of the configuration.

So the question is: How can we enhance the Log4Net AdoNetAppender to have the ability to refer to an already existing connection string defined in the connectionStrings section of the configuration?

The good news is that the team behind Log4Net is already working on this feature. The bad news is that as of now* this feature has not yet been released. This article describes how we can implement a simple solution ourselves.

1) Create a class that inherits from AdoNetAppender.
2) Next create a ConnectionStringName property that will set the Log4Net ConnectionString property to a connection string that is retrieved by the .Net ConfigurationManager.
3) Create a ConnectionStringName entry in the AdoNetAppender section of  your config file which maps to an existing connectionString in the connectionStrings section of your config file.

Sample Custom AdoNetAppender Class:

using System.Configuration;
using log4net.Appender;

namespace WebUI.Infrastructure
{
    public class MyCustomAdoNetAppender : AdoNetAppender
    {
        public string ConnectionStringName
        {
            set { ConnectionString = ConfigurationManager.ConnectionStrings[value].ToString(); }
        }
    }
}

Sample Configuration File:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>  
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
  </configSections>
  <log4net>    
      <appender name="AdoNetAppender" type="WebUI.Infrastructure.MyCustomAdoNetAppender">
        <bufferSize value="1" />      
        <connectionType value="System.Data.SqlClient.SqlConnection, System.Data, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
        <ConnectionStringName value="MyConnectionName"/>      
        <!--Additional Info goes here -->
      </appender>
    <root>
      <level value="All"/>    
      <appender-ref ref="AdoNetAppender" />
    </root>
  </log4net>
  <connectionStrings>
      <add name="MyConnectionName"
       providerName="System.Data.ProviderName"
       connectionString="Valid Connection String;" />
  </connectionStrings>
</configuration>


* 03/26/2011