public void AddToCard(string userId, int productId, int quantity) { var card = _cardDal.GetCardByUserId(userId); if (card != null) { var index = card.CardItems.FindIndex(x => x.ProductId == productId); if (index < 0) { card.CardItems.Add(new CardItem() { ProductId = productId, Quantity = quantity, CardId = card.Id, }); } else { card.CardItems[index].Quantity += quantity; } _cardDal.Update(card); } }