.Net Core Project 從零開始 — NLog

William Liu

6 min readNov 23, 2019

Why use log?

在開發程式上，運作時很有可能會有一些莫名的錯誤或是功能異常，這些Log能協助你快速查詢確認問題點，確認問題點在哪之後對症下藥解決問題。

NLog官網:Link

Create ASP.NET Core project

2. Add dependency in csproj

使用.NET CLI

dotnet add package NLog --version 4.6.8dotnet add package NLog.Web.AspNetCore --version 4.9.0

3. Create a nlog.config file.

放在Asp .net core專案的root 資料夾上；以下是 nlog.config file example

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true"
      internalLogLevel="Info"
      internalLogFile="c:\temp\internal-nlog.txt">

  <!-- enable asp.net core layout renderers -->
  <extensions>
    <add assembly="NLog.Web.AspNetCore"/>
  </extensions>

  <!-- the targets to write to -->
  <targets>
    <!-- write logs to file  -->
    <target xsi:type="File" name="allfile" fileName="c:\temp\nlog-all-${shortdate}.log"
            layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}" />

    <!-- another file log, only own logs. Uses some ASP.NET core renderers -->
    <target xsi:type="File" name="ownFile-web" fileName="c:\temp\nlog-own-${shortdate}.log"
            layout="${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" />
  </targets>

  <!-- rules to map from logger name to target -->
  <rules>
    <!--All logs, including from Microsoft-->
    <logger name="*" minlevel="Trace" writeTo="allfile" />

    <!--Skip non-critical Microsoft logs and so log only own logs-->
    <logger name="Microsoft.*" maxlevel="Info" final="true" /> <!-- BlackHole without writeTo -->
    <logger name="*" minlevel="Trace" writeTo="ownFile-web" />
  </rules>
</nlog>

4. Enable copy to bin folder

5. program.cs, Set up NLog for Dependency injection

6. Configure appsettings.json

{
    "Logging": {
        "LogLevel": {
            "Default": "Trace",
            "Microsoft": "Information"
        }
    }
}

7. 接著就可以在程式上寫一點Log method 寫至 Log file了

由於在第5.的步驟已經進行過Nlog 的 Dependency injection ，可以直接在HomeController 的 constructor 取得到logger Service 使用它的方法

8.Run Web Site

在 nlog.config file裡範例將檔案寫至 temp folder底下

在nlog-won裡可以看到我們所寫的Log Message

nlog-all 就紀錄了整個站台運作的狀況

Conclusion:這篇算是基礎篇，先入門了解Nlog設定與了解怎麼使用寫Log，之後會分享更多像是增加寫入位置至資料庫或是在什麼時機寫入Log更好

下一篇 .Net Core Project 從零開始 — Use NLog wite log to database table.

.Net Core Project GitHub:Link

Thanks for your reading.

.Net Core Project 從零開始 — NLog

Written by William Liu