Redirect NLog logging output to file specified by the logger

Question

I want all messages to go to all.log file and if logSource property is set then message should also go to logSource file. If I uncomment the when filter then the logSource file is not created. I added when filter so it will include only message that had logSource set to non-null value.

Code

internal class Program
{
    private static readonly Logger _log = LogManager.GetCurrentClassLogger();

    static async Task Main(string[] args)
    {
        var logEvent = LogEventInfo.Create(LogLevel.Info, null, "message");
        logEvent.Properties["logSource"] = "Program";
        _log.Log(logEvent);

        _log.Info("This message should not be in the log since logSource is not set.");
    }
}

NLog.config

<?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"
  autoReload="true">

  <targets>
    <target xsi:type="File" name="fileInfo" fileName="all.log" 
        layout="${longdate}|${level}|${event-properties:logSource}"
      />
    <target xsi:type="File" name="fileInfoSource" fileName="${event-properties:logSource}.log" 
       layout="${longdate}|${level}|${event-properties:logSource}"
    />
  </targets>

  <rules>
    <logger name="*" minlevel="Info" writeTo="fileInfo"/>
    <logger name="*" minlevel="Info" writeTo="fileInfoSource">
      <filters>
        <!--when condition="not isset('${event-properties:logSource}')" action="Ignore" /-->
      </filters>
    </logger>
  </rules>
</nlog>

Answer 1

Alternative approach using WithProperty together with special Logger-Name for file-target redirection:

internal class Program
{
    private static readonly Logger _log = LogManager.GetCurrentClassLogger();
    private static readonly Logger _logSource = LogManager.GetLogger("LogSource");

    static async Task Main(string[] args)
    {
        GetLogSource("Program").Info("Message redirected to special place");        
        _log.Info("This message goes to the default place"):
    }

    static Logger GetLogSource(string logSource)
    {
        // Consider storing in class-variable when logSource is static
        return _logSource.WithProperty("LogSource", logSource);
    }
}

NLog.config

<?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"
  autoReload="true">

  <targets>
    <target xsi:type="File" name="fileInfo" fileName="all.log" />
    <target xsi:type="File" name="fileInfoSource" fileName="${event-properties:logSource:whenEmpty=MissingSource}.log" />
  </targets>

  <rules>
    <logger name="LogSource" minlevel="Info" writeTo="fileInfoSource" />
    <logger name="*" minlevel="Info" writeTo="fileInfo" />
  </rules>
</nlog>