Build E-Commerce Apps with Reactive Programming in Spring Boot/

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Adding Items to a Cart

Adding Items to a Cart

Learn how to add the functionality of adding items to the cart.

We'll cover the following...

How to add items to a cart

With these building blocks, it’s time to load up the cart. This is fundamental to any e-commerce system, so let’s get it right.

What are we trying to achieve?

  • We need to retrieve the current cart. If none exists, we need to create one.

  • If the item is already in the cart, we increment its quantity. If not, we add a new entry.

  • We need to save the updated cart.

To get this cart moving, we need to code the add/{itemId} operation that we called in the inventory table:

Java
@GetMapping
	Mono<Rendering> home() {
		...
	}
@PostMapping("/add/{id}") // <1>
Mono<String> addToCart(@PathVariable String id) { // <2>
	 return this.cartRepository.findById("My Cart") 
		.defaultIfEmpty(new Cart("My Cart")) // <3>
		.flatMap(cart -> cart.getCartItems().stream() // <4>
			.filter(cartItem -> cartItem.getItem() 
				.getId().equals(id)) 
			.findAny() 
			.map(cartItem -> {
				cartItem.increment();
				return Mono.just(cart);
			}) 
			.orElseGet(() -> { // <5>
				return this.itemRepository.findById(id) 
					.map(item -> new CartItem(item)) 
					.map(cartItem -> {
						cart.getCartItems().add(cartItem);
						return cart;
					});
				}))
			.flatMap(cart -> this.cartRepository.save(cart)) // <6>
			.thenReturn("redirect:/"); // <7>
	}
Adding an Item to the Cart

Wow! That’s a lot of code. Let’s explore the key parts.

  1. In line 5, @PostMapping maps this method onto POST /add/{id}. This lets the web page put a button on every item.

  2. In line 6, @PathVariable extracts the {id} part of the route into the method parameter named id.

  3. In line 8, there’s that Reactor Recipe again! Find ...