无法读取含点的appsettings.json键，NLog配置遇异常

问题背景 #

在NLog.Config中使用${configsetting}布局渲染器读取appsettings.json的日志级别配置时，普通名称（如Microsoft）能正常读取，但名称包含点的配置项（如Microsoft.Hosting.Lifetime）无法正确读取值。

环境配置示例 #

appsettings.json #

"Logging": {
    "LogLevel": {
      "Default": "Error",
      "Microsoft": "Information",
      "Microsoft.Hosting.Lifetime": "Error"
    }
}

正常工作的NLog规则（读取普通名称） #

<logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft}" writeTo="logfile,Loggly" />

无法工作的NLog规则（读取含点的名称） #

<logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft.Hosting.Lifetime}" writeTo="logfile,Loggly" />

已尝试的无效方法 #

• 使用单引号包裹：

  <logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel'.Microsoft.Hosting.Lifetime'}" writeTo="logfile,Loggly" />
  <logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.'Microsoft.Hosting.Lifetime'}" writeTo="logfile,Loggly" />
  

• 使用反斜杠转义点：

  <logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft\.Hosting\.Lifetime}" writeTo="logfile,Loggly" />
  

• 使用斜杠替代点：

  <logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft/.Hosting/.Lifetime}" writeTo="logfile,Loggly" />
  

• 使用方括号包裹：

  <logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel'.[Microsoft.Hosting.Lifetime]'}" writeTo="logfile,Loggly" />
  

编辑1：部分解决但规则不符合预期 #

尝试转义点（Microsoft\\.Hosting\\.Lifetime）后，配置能读取但日志规则行为不符合预期：

当前NLog.Config配置 #

<logger name="Microsoft.Hosting.Lifetime*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft\\.Hosting\\.Lifetime}" writeTo="logfile,Loggly" />
<logger name="Microsoft.Hosting.Lifetime*" maxlevel="${configsetting:item=Logging.LogLevel.Microsoft\\.Hosting\\.Lifetime}" writeTo="void" final="true" />
<logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft}" writeTo="logfile,Loggly" />       
<logger name="Microsoft*" maxlevel="${configsetting:item=Logging.LogLevel.Microsoft}" writeTo="void" final="true"/>
<logger name="*" minlevel="${configsetting:item=Logging.LogLevel.Default}" writeTo="logfile,Loggly" />

当前appsettings.json配置 #

"Logging": {
        "LogLevel": {
          "Default": "Information",
          "Microsoft": "Error",
          "Microsoft.Hosting.Lifetime": "Information"
        }
}

预期与实际差异 #

• 预期：Microsoft.Hosting.Lifetime的Information及以下级别日志被导向void目标
• 实际：仅Error及以下级别被导向void，推测读取的是Microsoft的日志级别值

NLog内部日志片段 #

2022-08-25 13:09:30.7512 Warn Logger: Microsoft.Hosting.Lifetime configured with duplicate output to target: FileTarget(Name=logfile). LoggingRule with NamePattern='Microsoft*' and Level=Error has been skipped.
2022-08-25 13:09:30.7512 Warn Logger: Microsoft.Hosting.Lifetime configured with duplicate output to target: FileTarget(Name=logfile). LoggingRule with NamePattern='*' and Level=Fatal has been skipped.
2022-08-25 13:09:30.7512 Debug Targets configured when LogLevel >= Trace for Logger: Microsoft.Hosting.Lifetime
2022-08-25 13:09:30.7512 Debug Logger Microsoft.Hosting.Lifetime [Trace] => void
2022-08-25 13:09:30.7678 Debug Logger Microsoft.Hosting.Lifetime [Debug] => void
2022-08-25 13:09:30.7678 Debug Logger Microsoft.Hosting.Lifetime [Info] => logfile Loggly void
2022-08-25 13:09:30.7678 Debug Logger Microsoft.Hosting.Lifetime [Warn] => logfile Loggly void
2022-08-25 13:09:30.7678 Debug Logger Microsoft.Hosting.Lifetime [Error] => logfile Loggly void
2022-08-25 13:09:30.7678 Debug Logger Microsoft.Hosting.Lifetime [Fatal] => logfile Loggly

解决方案 #

核心问题：配置路径解析与规则优先级 #

1. 正确读取含点的配置项：
   NLog的configsetting渲染器在处理带点的键名时，需要明确告知渲染器这是单个键而非嵌套路径。推荐两种写法：

   • 用单引号包裹完整路径，同时转义键内的点：

     ${configsetting:item='Logging.LogLevel.Microsoft\.Hosting\.Lifetime'}
     

   • 使用jsonpath参数直接指定JSON路径，逻辑更清晰：

     ${configsetting:jsonpath=Logging.LogLevel.'Microsoft.Hosting.Lifetime'}
     

2. 修正日志规则逻辑：
   原规则的问题在于minlevel和maxlevel的组合逻辑，以及规则执行顺序。要实现“指定级别及以下导向void”，需调整规则顺序和级别匹配方式：

   <!-- 先处理Microsoft.Hosting.Lifetime：将Information及以下级别导向void，终止后续规则 -->
   <logger name="Microsoft.Hosting.Lifetime*" maxlevel="${configsetting:jsonpath=Logging.LogLevel.'Microsoft.Hosting.Lifetime'}" writeTo="void" final="true" />
   <!-- 允许Microsoft.Hosting.Lifetime高于目标级别的日志输出 -->
   <logger name="Microsoft.Hosting.Lifetime*" minlevel="${configsetting:jsonpath=Logging.LogLevel.'Microsoft.Hosting.Lifetime'}:above" writeTo="logfile,Loggly" />
   
   <!-- 处理其他Microsoft前缀日志 -->
   <logger name="Microsoft*" maxlevel="${configsetting:item=Logging.LogLevel.Microsoft}" writeTo="void" final="true" />
   <logger name="Microsoft*" minlevel="${configsetting:item=Logging.LogLevel.Microsoft}:above" writeTo="logfile,Loggly" />
   
   <!-- 全局规则 -->
   <logger name="*" minlevel="${configsetting:item=Logging.LogLevel.Default}" writeTo="logfile,Loggly" />
   

   解释：

   • :above后缀表示“高于指定级别”，例如目标级别是Information时，minlevel=Information:above会匹配Warn及以上级别
   • 先执行maxlevel的void规则并标记final，确保符合条件的日志不会进入后续规则

3. 验证配置读取：
   开启NLog内部日志确认配置读取状态：

   <internalLogFile="nlog-internal.log" internalLogLevel="Debug" />
   

   查看日志中是否有类似ConfigSettingParser Found value 'Information' for path 'Logging.LogLevel.Microsoft.Hosting.Lifetime'的条目，确认配置读取正确。

内容的提问来源于stack exchange，提问作者Bala teja