Unable to set my connectionstring in NLog

Question

The NLog.config file does not set the connection string.

<?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="Warn"
      internalLogFile="c:\temp\internal-nlog.txt">

  <!-- Load the ASP.NET Core plugin -->
  <extensions>
    <add assembly="NLog.Web.AspNetCore" />
  </extensions>
  <variable name="SirNLogDb" value="data source=SQL_MULALLEY;initial catalog=LogFiles;User ID=xxx;Password=yyy;">
  </variable>
  <!--  providerName="System.Data.SqlClient"-->

  <!-- the targets to write to -->
  <targets>
    <target name="db"
            xsi:type="Database"
            dbProvider="System.Data.SqlClient"
            connectionString="${var:SirNLogDb}"
            commandType="StoredProcedure"
            commandText="[dbo].[NLog_AddEntry_p]">
      <parameter name="@machineName"    layout="${machinename}" />
      <parameter name="@siteName"       layout="${iis-site-name}" />
      <parameter name="@logged"         layout="${date}" />
      <parameter name="@level"          layout="${level}" />
      <parameter name="@username"       layout="${aspnet-user-identity}" />
      <parameter name="@message"        layout="${message}" />
      <parameter name="@logger"         layout="${logger}" />
      <parameter name="@properties"     layout="${all-event-properties:separator=|}" />
      <parameter name="@serverName"     layout="${aspnet-request:serverVariable=SERVER_NAME}" />
      <parameter name="@port"           layout="${aspnet-request:serverVariable=SERVER_PORT}" />
      <parameter name="@url"            layout="${aspnet-request:serverVariable=HTTP_URL}" />
      <parameter name="@https"          layout="${when:inner=1:when='${aspnet-request:serverVariable=HTTPS}' == 'on'}${when:inner=0:when='${aspnet-request:serverVariable=HTTPS}' != 'on'}" />
      <parameter name="@serverAddress"  layout="${aspnet-request:serverVariable=LOCAL_ADDR}" />
      <parameter name="@remoteAddress"  layout="${aspnet-request:serverVariable=REMOTE_ADDR}:${aspnet-request:serverVariable=REMOTE_PORT}" />
      <parameter name="@callSite"       layout="${callsite}" />
      <parameter name="@exception"      layout="${exception:tostring}" />
    </target>
  </targets>

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

I put a breakpoint and the connection string is null;

My Startup method is as follows;

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvcCore()
            .AddMvcOptions(o => o.OutputFormatters.Add(
                new JsonOutputFormatter(new JsonSerializerSettings(), ArrayPool<char>.Shared)));
        var connectionStringMSurveyV2 = Configuration.GetConnectionString("MSurveyV2Db");
        services.AddScoped<MSurveyV2Db>(_ => new MSurveyV2Db(connectionStringMSurveyV2));
        var connectionStringSir = Configuration.GetConnectionString("SirDb");
        services.AddScoped<SirDb>(_ => new SirDb(connectionStringSir));
        services.AddScoped<IPropertiesRepo, PropertiesRepo>();
        services.AddScoped<ISirUoW, SirUoW>();
        services.AddScoped<Services.IMailService, Services.MailService>();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole();
        loggerFactory.AddDebug();
        loggerFactory.AddNLog();
        //add NLog.Web
        app.AddNLogWeb();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler();
        }

        app.UseMvc();
        AutoMapper.Mapper.Initialize(cfg =>
        {
            cfg.CreateMap<Exception, OperationStatus>();
            cfg.CreateMap<ViewSelectedContracts, ContractDto>();
        });
        var logger = LogManager.GetCurrentClassLogger();
        logger.Info("Logged in");
    }
}

EDIT - I change the logger rule to <logger name="*" minlevel="Trace" writeTo="db" /> but still it didn't output anything. However I looked for the c:\temp\internal-nlog.txt and it had not been created. So it appears the nlog.config file is being ignored. But it is in my project next to the Startup.cs file.

EDIT2: - the null configuration can be solved by setting "Copy to output directory" to "copy always". From the comments underneath I have now got this working.

Answer 1

Another option is to create and register a custom NLog layout-renderer (startup.cs):

https://github.com/NLog/NLog/wiki/How-to-write-a-custom-layout-renderer

Which outputs the ConnectionString after having read it from your favorite configuration-location. Then you don't have the connectionstring in your nlog.config, but just refer to your custom layout-renderer.

Maybe cheer for this pending issue:

https://github.com/NLog/NLog.Web/issues/107

Answer 2

Updated answer

Since NLog.Web.AspNetCore 4.8 (NLog.Extensions.Logging 1.4 for .NET Core console programs) you could directly read from your appSettings.json

${configsetting:name=MyConnectionString}

see docs

---

Original answer

Unfortunately reading connectionstrings/settings from appSettings.json / app.config is not yet supported in NLog for .NET core.

Two options:

1. Set the connectionstring programmatically, by using variables. In your nlog.config:

   <target ... connectionString="${var:myConnectionstring}"  ... />
   

   and in code: (e.g. in Configure)

   LogManager.Configuration.Variables["myConnectionstring"] = "...."; //read config here
   

2. Or, set the connectionstring in nlog.config.

   In your nlog.config:

   <variable name="myConnectionstring" value="...." />  
   

   and using in your target in nlog.config:

   <target ... connectionString="${var:myConnectionstring}" ... />