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How to use LoggerMessage in ASP.NET Core

Updated: Mar 18, 2023

ASP.NET Core is a popular web framework that allows developers to build modern, high-performance web applications using the .NET platform. When developing applications, it is important to have a robust logging system in place to help diagnose issues and monitor the application's behavior. ASP.NET Core provides a built-in logging system that can be extended using the LoggerMessage class. In this article, we will explore how to use LoggerMessage in ASP.NET Corel.

What is LoggerMessage?

LoggerMessage is a class provided by Microsoft.Extensions.Logging namespace in ASP.NET Core. It is a lightweight way to define logging messages and associated metadata in a performant manner. LoggerMessage allows you to define log messages as static methods that can be called from throughout your application. This provides several benefits, including improved performance, reduced memory usage, and improved consistency.

How to use LoggerMessage in ASP.NET Core?

Using LoggerMessage in ASP.NET Core is straightforward. Here are the steps to follow:

STEP 1: Add the Microsoft.Extensions.Logging NuGet package to your project. You can do this using the Package Manager Console in Visual Studio or by using the .NET CLI:

dotnet add package Microsoft.Extensions.Logging

STEP 2: Define the logger category. This is a unique string that identifies the logger. It is typically defined as a constant in a static class:

public static class MyLoggerCategories
    public const string MyCategory = "MyNamespace.MyClass";

STEP 3: Define the logger messages. These are static methods that return an instance of the LoggerMessage type:

public static class MyLoggerMessages
    public static readonly Action<ILogger, string, Exception> MyMessage = LoggerMessage.Define<string>(
        new EventId(1000, "MyEvent"),
        args => $"My custom message: {args}");

    public static readonly Action<ILogger, Exception> MyError = LoggerMessage.Define(
        new EventId(1001, "MyError"),
        "An error occurred while processing the request.");

In the above example, we have defined two logger messages: MyMessage and MyError. MyMessage takes a single string argument and formats a custom message. MyError is a simple error message with no arguments.

STEP 4: Use the logger messages in your code. To use the logger messages, you first need to obtain an instance of the ILogger interface. This can be done using dependency injection:

public class MyController : Controller
    private readonly ILogger<MyController> _logger;

    public MyController(ILogger<MyController> logger)
        _logger = logger;

    public IActionResult MyAction()
        _logger.LogInformation(MyLoggerMessages.MyMessage, "Hello, world!");
        _logger.LogError(MyLoggerMessages.MyError, "An error occurred.");
        return Ok();

In the above example, we have injected an instance of the ILogger interface into our controller. We then use the LogInformation and LogError methods to log messages using the MyMessage and MyError logger messages defined earlier.


LoggerMessage is a powerful tool for defining logging messages in ASP.NET Core. By using static methods, you can define log messages in a performant and consistent manner. This makes it easy to add logging to your application and helps to ensure that your log messages are consistent and easy to understand. By following the steps outlined in this article, you should now be able to start using LoggerMessage in your ASP.NET Core applications.

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