public class SqlAppender : AppenderSkeleton
{
    private static readonly string CommandText = "INSERT INTO Log ([Date],[Thread],[Level],[Logger],[Message],[Exception]) VALUES (@log_date, @thread, @log_level, @logger, @message, @exception)";
 
    public string ConnectionString { get; set; }
 
    protected override void Append(LoggingEvent loggingEvent)
    {
        using (var conn = new SqlConnection(ConnectionString))
        using (var cmd = new SqlCommand(CommandText, conn))