How do I filter an nlog logger to contain only lines containing a substring?

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I have read the docs on this, but I can't get an NLog logger to contain only lines that contain a fixed substring. I am using the code below. The file is written but contains all logging output, just the same as another log I have that has no filter.

Can anyone please tell me what I am doing wrong?

<rules>
<logger name="*" minlevel="Trace" writeTo="DataStore">
<filters>
<when condition="contains('${message}','XXXX')" action="LogFinal"/>
</filters>
</logger>
</rules>

What I have tried:

I honestly can't think of what else to try right now. The above code looks dead simple and I don't see why it shouldn't work.

Posted 12-Sep-17 2:17am

Patrick Skelton

Updated 12-Sep-17 7:17am

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Patrick Skelton · Accepted Answer · 2017-09-12T07:17:00

Solution 1

The answer to this is (as I suspected) annoyingly obvious. The clue is in the name. These things are called 'filters', so they don't say what should be written to the log; they say what should not be written to the log.

So, it works if I change the filter to:

<when condition="not contains('${message}','XXXX')" action="Ignore"/>

Posted 12-Sep-17 7:17am

Patrick Skelton

Comments

Richard Deeming 12-Sep-17 15:58pm

The term "filter" seems to be used interchangeably to mean both "only include items that match this" and "don't include items that match this", so it's not as obvious as you might think! :)

Patrick Skelton 13-Sep-17 3:30am

Very good point. I have to say that I found the whole thing - including the documentation - to be less than intuitive.