Change dynamically file path for log files .NET Core + NLog

问题

In my .NET Core app I use some environments and I want to do different paths to log files for every environment.

For example,

Development - c:\logs
Staging - d\apps\logs

For every environment I have config section in appsettings.{env}.json:

"LocalPaths": {
    "LogFileRootDirectory": "c:\\logs\\"
}

And part of nlog.config:

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true"
      internalLogLevel="Warn"
      internalLogFile="${logFileRootDirectory}internal-nlog.txt">
    ...
</nlog>

What's the best way to implement that?

回答1:

You could use (NLog) variables.

e.g.

<targets>
    <target name="file" xsi:type="File"
        fileName="${var:mydir}/logfile.txt" ... >

and in C#

LogManager.Configuration.Variables["mydir"] = "c:\logs";

When you change the variable, the path is automatically changed - no reload needed.

See also the docs for ${var}

Update: you could change the LogManager.Configuration after:

env.ConfigureNLog("nlog.config");

e.g. your startup.cs could look like this:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, 
                      ILoggerFactory loggerFactory)
{
    //add NLog to ASP.NET Core
    loggerFactory.AddNLog();

    //add NLog.Web
    app.AddNLogWeb();

    //configure nlog.config in your project root. 
    env.ConfigureNLog("nlog.config");


    LogManager.Configuration.Variables["mydir"] = "c:\logs";
    ...

回答2:

NLog.Extension.Logging ver. 1.4 supports ${configsetting} for reading directly from appsetting.json:

<targets>
    <target name="file" xsi:type="File"
        fileName="${configsetting:LocalPaths.LogFileRootDirectory}/logfile.txt" ... >

See also: https://github.com/NLog/NLog/wiki/ConfigSetting-Layout-Renderer

回答3:

As they state it on their GitHub repository:

.NET Core issues:

${basedir} isn't working will in .NET Core

LogManager.GetCurrentClassLogger() will use the filename instead of the full class name (class name and namespace, like in NLog 4). This will be fixed in the final of NLog 5 (after the release of NETSTANDARD 2.0)

So you can't do that right now. Maybe they will fix that in the future.

来源：https://stackoverflow.com/questions/42945483/change-dynamically-file-path-for-log-files-net-core-nlog

标签

asp.net-core

nlog