Mediator Pattern in C#: Implementing with MediatR

MediatR implements the mediator pattern in .NET, decoupling request handling from the caller. It’s become my go-to for organizing application logic.

Setup

dotnet add package MediatR
dotnet add package MediatR.Extensions.Microsoft.DependencyInjection

services.AddMediatR(typeof(Startup));

Request and Handler

public class GetUserQuery : IRequest<UserDto>
{
    public int UserId { get; set; }
}

public class GetUserHandler : IRequestHandler<GetUserQuery, UserDto>
{
    private readonly IUserRepository _repo;
    
    public GetUserHandler(IUserRepository repo) => _repo = repo;
    
    public async Task<UserDto> Handle(GetUserQuery request, CancellationToken ct)
    {
        var user = await _repo.GetByIdAsync(request.UserId);
        return new UserDto { Id = user.Id, Name = user.Name };
    }
}

Using in Controller

[HttpGet("{id}")]
public async Task<ActionResult<UserDto>> Get(int id)
{
    var user = await _mediator.Send(new GetUserQuery { UserId = id });
    return Ok(user);
}

Benefits

• Decoupled handlers – easy to test
• Pipeline behaviors for cross-cutting concerns
• Clean controller actions

References

• MediatR GitHub