Add Custom Fields using Log4Net dynamically in c#

Question

I am trying to add some custom fields in my log using c#. I am able to do that when I know about all the fields.

Now, in one scenario I don't know the number of fields. E.g. I have to add the parameters of the object and the numbers of object will keep on changing during run-time and I need to add the fields depending upon the number of objects.

Is there any tweak can be done in log4net to accomplish this so whenever there is a new Object the new field get created.

I am not sure mainly how to handle this in the config file for log4net.

Answer 1

You can add the properties of your object in a custom property for log4net and log the content of the property in your formatting:

For example in your code:

log4net.ThreadContext.Properties[ "myObjectProperties" ] = obj.prop1 + " " obj.prop2; // + ...;

and in the configuration:

 <conversionPattern value="%logger (%property{myObjectProperties}) [%level]- %message%newline" />

You cannot have a pattern that is configurable on the fly; you could have multiple patterns that would match different objects but this won't be very easy to manage.

EDIT: well, you could have a runtime configurable pattern but not natively :) However you could perhaps have a pattern that is able to be loaded from the aforementioned properties

2nd EDIT: If there are as much as 4000 properties you need, why not consider either pushing all those properties as part of the message itself (log.Info(myObject.ToString())) or create a custom appender that would be able to handle a specific interface to process:

public interface IHaveManyFieldsToLog
{
    public string[] GetAllPropertyValues()
}

public class ManyFieldsToLogAppender: SkeletonAppender
{
    // pseudocode, I don't have the IDE at the moment
    public override AppendLog(LogEvent event)
    {
         if (event.Parameter[0] as IHaveManyFieldsToLog != null)
         {
              var values = (event.Parameter[0] as IHaveManyFieldsToLog).GetAllPropertyValues();
              // concat all values and push it to the log
         }
    }
}