Records simplify dependency injection for MediatR handlers

Writing MediatR handlers requires boilerplate. Records come to rescue

Profile pictureToni Petrina
Published on 2022-11-071 min read
  • #csharp
  • #mediatr

MediatR command handlers when used with dependency injection often feel... boilerplatey.

Let's look at an example handler with two injected services.

public sealed class SendEmailCommandHandler
    : IRequestHandler<int, int>
    private readonly IEmailSender _emailSender;
    private readonly IUserRepository _userRepository;
    private readonly ILogger _logger;

    public SendEmailCommandHandler(
        IEmailSender emailSender,
        IUserRepository userRepository,
        ILogger logger
        _emailSender = emailSender;
        _userRepository = userRepository;
        _logger = logger;

    // of the handler goes below

As seen on the above example, creating a constructor, fields and assigning them is a bit repetitive. Even with modern tooling, it still feels as...not really necessary.

Enter records. With its feature of primary constructors, the above code can be simplified to:

public sealed record SendEmailCommandHandler(
        IEmailSender _emailSender,
        IUserRepository _userRepository,
        ILogger _logger
    ) : IRequestHandler<int, int>
    // of the handler goes below

If you squint, it almost looks like a public method definition. Quite a nice improvement: shorter file and easier on the eyes.

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