NLog with an Entity Framework connection string?

This problem can be easily solved by configuring logging target in code:

    private DatabaseTarget CreateDatabaseTarget()
    {
        var entityFrameworkConnection = ConfigurationManager.ConnectionStrings["MyEntities"].ConnectionString;
        var builder = new EntityConnectionStringBuilder(entityFrameworkConnection);
        var connectionString = builder.ProviderConnectionString;

        var target = new DatabaseTarget()
        {
            ConnectionString = connectionString,
            CommandText = @"insert into Log ([DateTime], [Message]) values (@dateTime, @message);",
            Parameters = {
                new DatabaseParameterInfo("@dateTime", new NLog.Layouts.SimpleLayout("${date}")), 
                new DatabaseParameterInfo("@message", new NLog.Layouts.SimpleLayout("${message}")), 
           }
        };
        return target;
    }

Then you can register it with your NLog configuration:

var target = CreateDatabaseTarget();
LogManager.Configuration.AddTarget("databaseTarget", CreateDatabaseTarget());
LogManager.Configuration.LoggingRules.Add(new NLog.Config.LoggingRule("*", LogLevel.Warn, target));

But if you're fine with taking some Nuget dependencies or want a more complete solution, you can take a look at NLog.Mvc and NLog.EntityFramework repositories who both have nuget packages available...

There is no way to customize the built in DatabaseTarget because it's sealed. And there aren't any other extension points because the DatabaseTarget.InitializeTarget() will always throw an exception because it cannot create the DbProviderFactory form the EF providerName="System.Data.EntityClient"

So with the current NLog version 2.0.0.0 you have to following options:

1. You can duplicate the connection string or you can use the DatabaseTarget DB configuration attributes.
2. You can write your own custom target basically from scratch.
3. You can submit a feature request, and wait until it's implemented.