Clean Domain-driven Design article

CartItem.cs

public sealed class CartItem : EntityBase
{
  private CartItem() : base(GenerateId())
  {
  }

  private CartItem(Guid id, int quantity, double price = 0.0D, double promoSavings = 0.0D) : base(id)
  {
    Quantity = quantity;
    Price = price;
    PromoSavings = promoSavings;
  }

  public static CartItem Load(Guid productId, int quantity, double price = 0.0D, double promoSavings = 0.0D)
  {
    return Load(GenerateId(), productId, quantity, price, promoSavings);
  }

  public static CartItem Load(Guid id, Guid productId, int quantity, double price, double promoSavings)
  {
    return new CartItem(id, quantity, price, promoSavings).LinkProduct(productId);
  }

  [Required] public int Quantity { get; private set; }

  [Required] public double Price { get; private set; }

  [Required] public double PromoSavings { get; private set; }

  public Cart Cart { get; private set; }
  public Guid CartId { get; private set; }

  public Product Product { get; private set; }

  public CartItem LinkCart(Cart cart)
  {
    Cart = cart;
    CartId = cart.Id;
    return this;
  }

  public CartItem LinkProduct(Guid productId)
  {
    var product = Product.Load(productId);
    product.LinkCartItem(this);
    Product = product;
    return this;
  }

  public CartItem FillUpProductInfo(string name, double price, string desc)
  {
    Product = Product.Load(Product.ProductId, name, price, desc);
    return this;
  }

  public CartItem ChangePrice(double price)
  {
    Price = price;
    return this;
  }

  public CartItem ChangePromoSavings(double promoSavings)
  {
    PromoSavings = promoSavings;
    return this;
  }

  public CartItem AccumulateQuantity(int quantity)
  {
    Quantity += quantity;
    return this;
  }
}