Serilog Filter Sink by Custom Property

Question

I want to use Serilog.Expressions to filter my logging for a specific sink. In this instance, I only want to log to the Console Sink if my custom property MethodName is equal to "SomeOtherTask". Serilog is still logging to both Sinks for DoSomeWork and SomeOtherTask . Is there something wrong with my filter expression or how I have implemented my custom property MethodName or something else?

appsettings.json:

{
    "Serilog": {
        "Using": [ "Serilog.Sinks.Console", "Serilog.Sinks.File", "Serilog.Expressions" ],
        "MinimumLevel": "Debug",
        "WriteTo": [
            {
                "Name": "Console",
                "Filter": [
                    {
                        "Name": "ByIncludingOnly",
                        "Args": {
                            "expression": "MethodName = 'SomeOtherTask'"
                        }
                    }
                ]
            },
            {
                "Name": "File",
                "Args": {
                    "path": "Logs/log.txt"
                }
            }
        ],
        "Enrich": [ "FromLogContext", "WithMachineName", "WithThreadId" ],
        "Properties": {
            "Application": "SerilogSplitLogTest"
        }
    }
}

Program.cs:

internal class Program
{
    static void Main()
    {
        var builder = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json", true, true);
        
        var config = builder.Build();

        var logger = new LoggerConfiguration()
            .ReadFrom.Configuration(config)
            .CreateLogger();

        new Program().Run(logger);

        Console.ReadKey(true);
    }

    public void Run(ILogger logger)
    {
        DoSomeWork(logger);
        SomeOtherTask(logger);
    }

    public void DoSomeWork(ILogger logger)
    {
        logger.Information("This should log to File");
    }

    public void SomeOtherTask(ILogger logger)
    {
        using (LogContext.PushProperty("MethodName", nameof(SomeOtherTask)))
        {
            logger.Information("This should log to Console");
        }
    }
}

Answer 1

I had similar issues of writing to 2 files, 1 was to have all the logging and there other was to be filtered by a property so it was a kind of condensed log. Here is how I did it.

First, make sure you install Serilog.Expressions . Doing this alone may solve your issue, if not then here is my WriteTo section of my config that I used.

Note: Marker is the custom property I was filtering on.

"WriteTo": [
  {
    "Name": "Logger",
    "Args": {
      "configureLogger": {
        "Filter": [
          {
            "Name": "ByIncludingOnly",
            "Args": {
              "expression": "Marker is not null"
            }
          }
        ],
        "WriteTo": [
          {
            "Name": "File",
            "Args": {
              "path": "D:\\Temp\\SerilogTesting.txt",
              "outputTemplate": "[{Timestamp:yyyy-MM-dd HH:mm:ss.fff}] - [{Level:u3}] - [{SourceContext}.{Method}] - {Message:lj}{NewLine:1}{Exception:1}",
              "rollingInterval": "Day",
              "retainedFileCountLimit": 7,
              "shared": true
            }
          }
        ]
      }
    }
  },
  {
    "Name": "File",
    "Args": {
      "path": "D:\\Temp\\SerilogTesting.log",
      "outputTemplate": "[{Timestamp:yyyy-MM-dd HH:mm:ss.fff}] - [{Level:u3}] - [{SourceContext}.{Method}] - {Message:lj}{NewLine:1}{Exception:1}",
      "rollingInterval": "Day",
      "retainedFileCountLimit": 7,
      "shared": true
    }
  },
  {
    "Name": "Console",
    "Args": {
      "theme": "Serilog.Sinks.SystemConsole.Themes.AnsiConsoleTheme::Code, Serilog.Sinks.Console",
      "outputTemplate": "[{Marker}][{Timestamp:yyyy-MM-dd HH:mm:ss.fff}] - [{Level:u3}] - [{SourceContext}.{Method}] - {Message:lj}{NewLine:1}{Exception:1}"
    }
  }
]

Then my property was pushed like so

_logger.ForContext("Marker","LW").Information("Something to log");