UserController.cs

public class UsersController : ControllerBase 
{
	private readonly IMediator _mediator;

	public UsersController(IMediator mediator) {
		_mediator = mediator ?? throw new ArgumentNullException(nameof(mediator));
	}

	[HttpGet("{id}")]
	public async Task<Order> Get(int id) {
    	var user = await _mediator.Send(new GetUserDetailQuery(id));
        if user == null {
        	return NotFound();
        }
        return Ok(user);
    }
}