Chris Padilla/Blog / Tech

Dependency Injection and Logging in .NET

Buy in large, server logs come out of the box with .NET Core. Setting up logging for you controllers, however, takes just a little bit of setup.

In console applications, logging is straightforward:

System.Console.WriteLine("Hello World");

In a .NET application, though, you'll likely need to pipe your logs through the logger class from your Dependency Injection.

Here's a look at a bare bones Controller:

using Microsoft.AspNetCore.Mvc;
namespace Bookshelf_cs.Controllers;
using Bookshelf_cs.Data;
using Bookshelf_cs.Models;

public class AuthorController : ControllerBase

    private readonly ILogger<AuthorController> _logger;

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


In the constructor, we're constructing our controller with a _logger attribute.

An aside on Dependency Injection

So why is this better than just instantiating a logger class directly? Like so:

private readonly ILogger<AuthorController> _logger = new Logger();

The short answer is to avoid tight coupling. By using the ILogger interface, you can swap out the default Microsoft logger with a custom logger so long as it shares the same interface. More details with examples on MSDN.

That swapping out happens at your app building stage in your Program.cs file. If we wanted to customize the logger, it would look like this:

// Program.cs

var builder = WebApplication.CreateBuilder(args);

ConfigurationManager configuration = builder.Configuration;


var app = builder.Build();

Very DRY. If you need to make changes, it's all done at the application level. From there, the builder injects your logger of choice into your classes that accept a logger in their constructors.


Once it's instantiated in your class, you can log directly from the _logger attribute:

_logger.LogInformation(1001, "Author passed");
_logger.LogWarning(1001, obj.ToString());

For any custom changes for what level of logs are displayed, you can tweak the appsettings.json file:

  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.AspNetCore.SpaProxy": "Information",
      "Microsoft.Hosting.Lifetime": "Information"