Remove Log4net (null): Conditional Output - log4net

Question

I'm trying to suppress "(null)" output. If I have this conversionPattern:
%property{MyProp}
...and if MyProp is null, then the output is:
(null)
In most cases that is good. But what if I don't want the "(null)" to be output? Can this be done?
The problem becomes more interesting if my conversionPattern looks like this:
MY_PROP=%property{MyProp}
In this case, even if I find a way to suppress the "(null)", my output will still be:
MY_PROP=
Ideally, I'd like to suppress everything related to "my prop" if the value is null. If I invented my own syntax, it might be:
%(MyProp,MY_PROP=%MyProp)
This would make log4net suppress the conversion pattern specified in the second parameter, if the first parameter was null.
My musings aside, is there a real way to do this in log4net?

Answer 1

One way to do this is to create a custom PatternLayoutConverter. If the property value is null write the customNullReplacement (that can even be based on the Option key if you want some dynamism).
namespace LogUtils
{
public class CustomNullProperty : PatternLayoutConverter
{
private static string customNullReplacement = "????";
override protected void Convert(TextWriter writer, LoggingEvent loggingEvent)
{
if (Option != null)
{
var prop = loggingEvent.LookupProperty(Option);
if(prop == null)
{
prop = customNullReplacement;
}
WriteObject(writer, loggingEvent.Repository, prop);
}
else
{
WriteDictionary(writer, loggingEvent.Repository, loggingEvent.GetProperties());
}
}
}
}
You then define this converter – using the <converter> tag – on the Log4Net Configuration (XML based config example bellow) and use it on your conversionPattern:
<layout type="log4net.Layout.PatternLayout">
<converter>
<name value="customNullProp" />
<type value="LogUtils.CustomNullProperty, DLLNAME" />
</converter>
<conversionPattern value="customNullProp{PropertyName} %message%newline"/>
</layout>
There are other approaches like creating a renderer for System.Object but I find this approach more explicit.
For your second requirement, using the custom converter, you could simply move the prefix inside the custom converter writer.