Clean Domain-driven Design article - Add Product to a Cart

RequestHandler.cs

public class RequestHandler : TxRequestHandlerBase<InsertItemToNewCartRequest, InsertItemToNewCartResponse>
{
  private readonly ICatalogGateway _catalogGateway;
  private readonly IShippingGateway _shippingGateway;
  private readonly IPromoGateway _promoGateway;

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

  public override async Task<InsertItemToNewCartResponse> Handle(InsertItemToNewCartRequest request, CancellationToken cancellationToken)
  {
    var cartCommander = UnitOfWork.Repository<Domain.Cart>();

    var cart = await Domain.Cart.Load()
      .InsertItemToCart(request.ProductId, request.Quantity)
      .CalculateCartAsync(TaxType.NoTax, _catalogGateway, _promoGateway, _shippingGateway);

    await cartCommander.AddAsync(cart);
    await UnitOfWork.SaveChangesAsync(cancellationToken);

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