Nlog ${event-context:item=xxxx} not writing in logging database

Question

I have a Nlog configuration that is basically this:

\">
  &         


        

Answer 1

As it turned out, it was a bug (or a feature) in NLog. When writing to a 'target' in NLog asynchronously the original LogEventInfo that is written is added to the Parameters collection of a new LogEventInfo, thus the Properties collection where the {event-context} gets its values from is empty (because it is a new object). Resulting in the empty strings written to the database.

So, in order to solve this I added this function to << NLog 2.1 Source >>\Targets\Target.cs:

    private void MergeEventProperties(LogEventInfo logEvent)
    {
        foreach (var item in logEvent.Parameters)
        {
            if (item.GetType() == typeof(LogEventInfo))
            {

                foreach (var propertyItem in ((LogEventInfo)item).Properties)
                {
                    logEvent.Properties.Remove(propertyItem.Key);
                    logEvent.Properties.Add(propertyItem);
                }
            }
        }
    }

Then in the function protected virtual void Write(AsyncLogEventInfo logEvent) I changed this code

        try
        {
            this.Write(logEvent.LogEvent);
            logEvent.Continuation(null);
        }

into this:

        try
        {
            MergeEventProperties(logEvent.LogEvent);

            this.Write(logEvent.LogEvent);
            logEvent.Continuation(null);
        }

After that, my values were written to the database.

I hope it helps other people who are having this issue.