NLog Custom Log Level Value

I have a database I'm trying to write my开发者_JAVA技巧 messages to and would like to use the ${level} layout, but I need to translate it to the int value for reference to my own table that stores logging levels. Is it possible to maybe cast the level to my enum in config? Any other ideas?

I have not checked this, but I suspect you should be able to just write your own layout renderer (plugin) for NLog to do what you want to do. NLog is very pluggable :)

A quick example of how a layout renderer could look (not tested...):

[LayoutRenderer("intLevel", UsingLogEventInfo = true)]
public class IntLevel : LayoutRenderer
{
    protected override int GetEstimatedBufferSize(LogEventInfo logEvent)
    {
        return 1;
    }

    protected override void Append(StringBuilder builder, LogEventInfo logEvent)
    {
        switch(logEvent.Level.LowercaseName)
        {
            case "trace":
                builder.Append(0);
                break;
            case "debug":
                builder.Append(1);
                break;
            case "info":
                builder.Append(2);
                break;
            case "warn":
                builder.Append(3);
                break;
            case "error":
                builder.Append(4);
                break;
            case "fatal":
                builder.Append(5);
                break;
            default:
                builder.Append(-1);
                break;
        }
    }
}

Try this solution:

[LayoutRenderer("levelInt")]
public class NlogLevelToIntLayoutRenderer : LayoutRenderer
{
    protected override void Append(StringBuilder builder, LogEventInfo logEvent)
    {
        builder.Append(logEvent.Level.Ordinal);
    }
}

Here is a tested layout renderer that logs the log level as an integer. The way that I get the log levels is probably a little overboard, but I was going through a linq phase ;-)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using NLog;
using NLog.LayoutRenderers;

namespace MyNLogExtensions.NLog
{
  [LayoutRenderer("LogLevelOrdinal")]
  class LogLevelOrdinalLayoutRenderer : LayoutRenderer
  {
    IDictionary<LogLevel, int> ordinals;

    public override void  Initialize()
    {
      base.Initialize();

      ordinals = GetLogLevels()
                  .OrderBy(level => level)
                  .Select((level, index) => new { Level = level, Ordinal = index })
                  .ToDictionary( x => x.Level, x => x.Ordinal);
    }

    protected override void Append(StringBuilder builder, LogEventInfo logEvent)
    {
      int level = 0;

      if (!ordinals.TryGetValue(logEvent.Level, out level)) level = 99;

      builder.Append(level);
    }

    protected override int GetEstimatedBufferSize(LogEventInfo logEvent)
    {
      return 1;
    }

    //
    // LogLevel is a static class with a static member for each of the different log levels.
    // The LogLevel ordinal is not exposed publically (i.e. an ordinal indicating the relative
    // "importance" of a LogLevel value).
    // The implementation of LogLevel.GetHashCode actually does return the ordinal, but it doesn't
    // seem right to rely on that implementation detail.
    // In the end, this LayoutRenderer is really just to allow for producing a numeric value to represent
    // a particular log level value's "position" relative to the other lob levels.  As such, 
    // We can just get all of the known log level values, order them (they are sortable), and assign our
    // own ordinal based on the position of the log level value in the resulting sorted list.
    //
    // This helper function exposes the known log level values as IEnumerable<LogLevel> so that we can
    // easily use LINQ to build a dictionary to map LogLevel to ordinal.
    //
    internal IEnumerable<LogLevel> GetLogLevels()
    {
      yield return LogLevel.Trace;
      yield return LogLevel.Debug;
      yield return LogLevel.Info;
      yield return LogLevel.Warn;
      yield return LogLevel.Error;
      yield return LogLevel.Fatal;
    }

  }
}