Clean Domain-driven Design article - Get Cart with Products

RequestHandler.cs

public class RequestHandler : RequestHandlerBase<GetCartRequest, GetCartResponse>
{
  private readonly ICatalogGateway _catalogGateway;
  private readonly IShippingGateway _shippingGateway;
  private readonly IPromoGateway _promoGateway;

  public RequestHandler(ICatalogGateway cgw, IQueryRepositoryFactory qrf,
    IShippingGateway shippingGateway, IPromoGateway promoGateway)
    : base(qrf)
  {
    _catalogGateway = cgw;
    _shippingGateway = shippingGateway;
    _promoGateway = promoGateway;
  }

  public override async Task<GetCartResponse> Handle(GetCartRequest request, CancellationToken cancellationToken)
  {
    var cartQuery = QueryFactory.QueryEfRepository<Domain.Cart>();

    var cart = await cartQuery.GetFullCartAsync(request.CartId, false)
      .ToObservable()
      .SelectMany(async c =>
        await c.CalculateCartAsync(TaxType.NoTax, _catalogGateway, _promoGateway, _shippingGateway));

    return new GetCartResponse { Result = cart.ToDto() };
  }
}