Question

I’d like to use NLog to log to a RavenDb database. There is apparently no existing NLog Target for this (according to this, and searches), so I’m attempting to write my own. I keep getting in conflict with the RavenDb client’s own NLog config, and I can’t work out how to fix this. Here’s my Target:

namespace NLog.RavenDb
{
    class LogEntry
    {
        public string Id { get; set; }
        public Exception Exception { get; set; }
        public string LogLevel { get; set; }
        public StackTrace StackTrace { get; set; }
        public DateTimeOffset TimeStamp { get; set; }
        public string Message { get; set; }
    }

    public class RavenDbTarget : NLog.Targets.TargetWithLayout
    {
        public static IDocumentStore Store { get; set; }

        protected override void Write(LogEventInfo logEvent)
        {
            if (Store == null)
            {
                const string noStoreWarning = "No Document Store set for the RavenDb Log target";
                Debug.WriteLine(noStoreWarning);
                return;
            }

            LogEntry entry = new LogEntry
            {
                Exception = logEvent.Exception,
                LogLevel = logEvent.Level.Name,
                Message = logEvent.FormattedMessage,
                StackTrace = logEvent.StackTrace,
                TimeStamp = new DateTimeOffset(logEvent.TimeStamp)
            };

            using (var session = Store.OpenSession())
            {
                session.Store(entry);
                session.SaveChanges();
            }
        }
    }
}

And here’s how I can get it to work with a SimpleConfigurator:

RavenDbTarget.Store = new DocumentStore { Url = "http://localhost:8080/" };
RavenDbTarget.Store.Initialize();

NLog.Config.SimpleConfigurator.ConfigureForTargetLogging(new RavenDbTarget());
Logger logger = NLog.LogManager.GetLogger("Any");
logger.Info("Hi");

However, NLog.config is used by RavenDb too, so when I put references to my Target in there , it throws an exception at Store.Initialize(). Here’s what I tried in NLog.config (NLog.RavenDb is the name of my library project containing the RavenDb Target):

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    <extensions>
        <add assembly="Nlog.RavenDb"/>
    </extensions>

    <targets>
        <target xsi:type="NLog.RavenDb.RavenDbTarget" name="Raven"/>
        <target xsi:type="File" name="f" fileName="${basedir}/logs/${shortdate}.log"
                layout="${longdate} ${uppercase:${level}} ${message}" />
    </targets>

    <rules>
        <logger minlevel="Trace" name="Any" writeTo="Raven" />
    </rules>
</nlog>

How can I make my NLog.config file play nice with RavenDb’s use of it?

Answer 1

Found it. I missed the Target attribute on my target class as shown here.

[NLog.Targets.Target("RavenDb")]
public class RavenDbTarget : NLog.Targets.TargetWithLayout

The name parameter you pass to the Target attribute is the one you reference as “type” in your config file:

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    <extensions>
        <add assembly="Nlog.RavenDb"/>
    </extensions>

    <targets>
        <target xsi:type="RavenDb" name="Raven"/>
    </targets>

    <rules>
        <logger minlevel="Trace" name="Any" writeTo="Raven" />
    </rules>
</nlog>

Now NLog picks up NLog.config automatically, and I don’t need any extra config code. Here’s the contents of my test console app’s main method now:

        RavenDbTarget.Store = new DocumentStore { Url = "http://localhost:8080/" };
        RavenDbTarget.Store.Initialize();

        Logger logger = LogManager.GetLogger("Any");
        logger.Info("Hi");