CODEWITHSUNDEEP
c#loggingnlog
TheBoubou
TheBoubou

Reputation: 19903

Update NLog target filename at runtime

In my application, I work on several thousand of document a day. I'd like, in some cases some logs, one log by document. Then I'd like for a specific target change the output filename (and only the filename) at runtime.

Around the web I found how to create a target by programming me I'd like just update a the filename by programming. I tried the code below. The error I receive is "LayoutRender cannot be found 'logDirectory'.

Any idea ?

Thanks,

var target = (FileTarget)LogManager.Configuration.FindTargetByName("logfile");
target.FileName = "${logDirectory}/file2.txt";

LoggingConfiguration config = new LoggingConfiguration();
var asyncFileTarget = new AsyncTargetWrapper(target);
config.AddTarget("logfile", asyncFileTarget);

LogManager.Configuration = config;

The config file is :

  <nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <variable name="logDirectory" value="C:/MyLogs"/>
    <targets>
      <target name="logfile" xsi:type="File" layout="${date:format=dd/MM/yyyy HH\:mm\:ss.fff}|${level}|${stacktrace}|${message}" fileName="${logDirectory}/file.txt" />
    </targets>

    <rules>
      <logger name="*" minlevel="Info" writeTo="logfile" />
    </rules>    
  </nlog>

Upvotes: 28

Views: 42434

Answers (7)

spiairsh
spiairsh

Reputation: 21

This worked for me.

using NLog;
using NLog.Targets;
using NLog.Targets.Wrappers;

var target = LogManager.Configuration.FindTargetByName("logfile");
var asyncTarget = target as AsyncTargetWrapper;
var fileTarget = asyncTarget.WrappedTarget as FileTarget;
var file = fileTarget.FileName;
var archiveFile = fileTarget.ArchiveFileName;

//FileName and ArchiveFileName are of type Layout. ToString gives the string representaion. We can change it and assign it back. Remember to put .Trim('\'') for removing the extra single quotes that gets added while converting to string.

Upvotes: 1

Rolf Kristensen
Rolf Kristensen

Reputation: 19847

If not needing to change the LogDirectory at runtime, then you can do this:

target.FileName = "${var:logDirectory}\\file2.txt");

If needing to modify the logDirectory at runtime, then use the GDC:

https://github.com/NLog/NLog/wiki/Gdc-layout-renderer

NLog.GlobalDiagnosticsContext.Set("logDirectory","C:\Temp\");

Then you can use the following layout:

target.FileName = "${gdc:item=logDirectory}\\file2.txt";

Upvotes: 7

Mark
Mark

Reputation: 149

For anyone stuck on this, I finally found a solution. I was trying to update some syslog target settings at runtime and nothing was working. Simply updating the configuration does not work, you need to reset the Configuration object, which is as simple as doing this:

LogManager.Configuration = LogManager.Configuration;

This causes an internal event to fire and actually use the updated configuration.

Upvotes: 1

Flater
Flater

Reputation: 13763

I happen to have written an answer that fits your question as well.

In essence, instead of trying to rewrite the configuration, you'd be better off simply creating a configuration that allows you to dynamically choose the filename you want.

An adapted example for your use case:

Logger myLog = LogManager.GetLogger(name);
LogLevel level = LogLevel.Error;
string message = "This is an error message!";

You turn this information into a LogEventInfo object:

LogEventInfo logEvent = new LogEventInfo(level , myLog.Name, message);

You can then add properties to this event (the string indexes are free to choose): 

logEvent.Properties["CustomFileName"] = "mycustomfilename";

And then you write to the log:

myLog.Log(logEvent);

The interesting thing here is that in your NLog configuration, you can use this custom property in any field that the Nlog documentation refers to as a "Layout" value.

You use ${event-properties:item=CustomFileName} in the layout to access the property. For example:

<target xsi:type="File" 
        name="file" 
        fileName="${basedir}/logs/${event-properties:item=CustomFileName}.log"
        layout="${message}" />

Following the posted example, this message will be logged in the mycustomfilename.log file. This enables you to dynamically switch your targeted file as you please by setting the logEvent.Properties["CustomFileName"] value to whatever filename you want to use.

Note that you can further optimize this, and e.g. only be able to choose part of the file name.

The additional benefit is that you only need one target and one rule in your config file to make this work.

Upvotes: 0

Baddack
Baddack

Reputation: 2053

Tony's solution doesn't seem to work if you use NLog Async (<targets async="true">). I had to use the wrapper target to get my FileTarget, otherwise I get a lot of errors. I'm using NLog 2.1.

if (LogManager.Configuration != null && LogManager.Configuration.ConfiguredNamedTargets.Count != 0)
{
    Target target = LogManager.Configuration.FindTargetByName("yourFileName");
    if (target == null)
    {
        throw new Exception("Could not find target named: " + "file");
    }

    FileTarget fileTarget = null;
    WrapperTargetBase wrapperTarget = target as WrapperTargetBase;

    // Unwrap the target if necessary.
    if (wrapperTarget == null)
    {
        fileTarget = target as FileTarget;
    }
    else
    {
        fileTarget = wrapperTarget.WrappedTarget as FileTarget;
    }

    if (fileTarget == null)
    {
        throw new Exception("Could not get a FileTarget from " + target.GetType());
    }

    fileTarget.FileName = "SetFileNameHere";
    LogManager.ReconfigExistingLoggers();
}

This also doesn't change the config file, it just changes the runtime value. So I also manually edit the config file to my new value using the code below:

var nlogConfigFile = "NLog.config";
var xdoc = XDocument.Load(nlogConfigFile);
var ns = xdoc.Root.GetDefaultNamespace();
var fTarget = xdoc.Descendants(ns + "target")
         .FirstOrDefault(t => (string)t.Attribute("name") == "yourFileName");
fTarget.SetAttributeValue("fileName", "SetFileNameHere");
xdoc.Save(nlogConfigFile);

Upvotes: 6

Tony
Tony

Reputation: 7445

Try ReconfigExistingLoggers method:

var target = (FileTarget)LogManager.Configuration.FindTargetByName("logfile");
target.FileName = "${logDirectory}/file2.txt";
LogManager.ReconfigExistingLoggers();

As written in docs:

Loops through all loggers previously returned by GetLogger. and recalculates their target and filter list. Useful after modifying the configuration programmatically to ensure that all loggers have been properly configured.

EDIT:

Try use custom layout renderer: NLog config file to get configuration setting values from a web.config

Upvotes: 32

kravasb
kravasb

Reputation: 696

The reason why you get the error is that NLog knows nothing about "logDirectory" keyname. You may implement it by yourself (read instructions here) or use predefined ones from here.

Then you can use instructuions from here to change NLog targets during runtime.

Upvotes: 1

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