英文:
Why does Java function multiply the quantity when adding to cart?
问题
我正在尝试将新产品添加到购物车。当我添加第一个产品时，它会被正确添加。当产品已存在时，它会正确递增，但是当购物车中已经存在产品并尝试添加新产品时，数量会增加1个。
protected void addToCart(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
int productId = Integer.parseInt(request.getParameter("productId"));
if (session.getAttribute("cart") == null) {
ArrayList<Item> item = new ArrayList<>();
item.add(new Item(ProductModel.getProduct(productId), 1));
session.setAttribute("cart", item);
} else {
ArrayList<Item> item = (ArrayList<Item>) session.getAttribute("cart");
boolean productExists = false;
for (int i = 0; i < item.size(); i++) {
// This line increments the quantity of the existing product correctly
if (item.get(i).getProduct().getId() == productId) {
item.get(i).setQuantity(item.get(i).getQuantity() + 1);
productExists = true;
break; // Exit the loop since product is found
}
}
if (!productExists) {
// Here, add the new product to the cart with quantity 1
item.add(new Item(ProductModel.getProduct(productId), 1));
}
session.setAttribute("cart", item);
}
}
可能的问题是，您在遍历现有购物车项目时，对于每个项目都尝试将新产品添加到购物车。为了解决这个问题，我在代码中添加了一个布尔变量productExists来跟踪是否已经存在该产品，并相应地调整了代码逻辑。如果产品已存在，我在其数量上进行递增。如果不存在，我才将新产品添加到购物车。这样可以避免重复添加相同的产品。
英文:
I am trying to add a new product into cart. When I add the first product, it's added correctly. When the product already exist, it increment correctly but when there are products existing into cart and try to add a new product it adds 1 more in quantity.
protected void addToCart(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
int productId = Integer.parseInt(request.getParameter("productId"));
if (session.getAttribute("cart") == null) {
ArrayList<Item> item = new ArrayList<>();
item.add(new Item(ProductModel.getProduct(productId), 1));
session.setAttribute("cart", item);
} else {
ArrayList<Item> item = (ArrayList<Item>) session.getAttribute("cart");
for (int i = 0; i < item.size(); i++) {
// This line increment the product correctly
if (item.get(i).getProduct().getId() == productId) {
item.get(i).setQuantity(item.get(i).getQuantity() + 1);
} else {
// Here the product is added twice instead of once
item.add(new Item(ProductModel.getProduct(productId), 1));
}
session.setAttribute("cart", item);
}
}
}
What would be the problem?
答案1
得分: 1
问题是，当找到一个没有相同产品ID的项目时，代码会向购物车中添加新项目。它应该这样做：只有当没有项目具有相同的产品ID时，才添加新项目。
您可以使用一个布尔变量来跟踪是否找到具有匹配产品ID的项目，如果在循环中没有找到，则在循环中添加新项目。
boolean foundExistingProduct = false;
ArrayList<Item> item = (ArrayList<Item>) session.getAttribute("cart");
for (int i = 0; i < item.size(); i++) {
if (item.get(i).getProduct().getId() == productId) {
item.get(i).setQuantity(item.get(i).getQuantity() + 1);
session.setAttribute("success", "已将现有产品添加到购物车！");
request.getRequestDispatcher("Products").forward(request, response);
foundExistingProduct = true;
break;
}
}
if (!foundExistingProduct) {
item.add(new Item(ProductModel.getProduct(productId), 1));
session.setAttribute("success", "已将另一产品添加到购物车！");
request.getRequestDispatcher("Products").forward(request, response);
}
session.setAttribute("cart", item);
英文:
The problem is that the code adds a new item to the cart when you find an item that doesn't have the same product ID. What it should be doing is add a new item if no item has the same product ID.
You can use a boolean variable to keep track of whether you found an item with a matching product ID or not, and add a new item in the loop if you did not.
boolean foundExistingProduct = false;
ArrayList<Item> item = (ArrayList<Item>) session.getAttribute("cart");
for (int i = 0; i < item.size(); i++) {
if (item.get(i).getProduct().getId() == productId) {
item.get(i).setQuantity(item.get(i).getQuantity() + 1);
session.setAttribute("success", "An existing product is added to shopping cart!");
request.getRequestDispatcher("Products").forward(request, response);
foundExistingProduct = true;
break;
}
}
if (!foundExistingProduct) {
item.add(new Item(ProductModel.getProduct(productId), 1));
session.setAttribute("success", "Another product is added to shopping cart!");
request.getRequestDispatcher("Products").forward(request, response);
}
session.setAttribute("cart", item);
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