Shopping context modelling

Question

I want to write my first application (e-commerce) in a DDD manner and I'd like to know whether I'm getting everything right so I want your opinion on my modelling - how can it be improved, what should I look for etc. Every feedback will be greatly appreciated.

I've divided my application into several bounded contexts (catalog, shopping, ordering) and below example is based on the shopping one. I am trying to use CQRS as well (thus AddProductToCart command).

My business requirements are as follows:

Customer should be able to add product to his cart
Price for added product should be specific to user and is based on several factors: (global discounts, user discounts and customer country (some countries have lowered base prices)

I've recognised following actors (please note comments on methods and classes):

/**
 * A customer (Aggregate Root) having an unique cart
 */
class Customer
{
    /**
     * @var int
     */
    private $customerId;

    /**
     * @var string
     */
    private $country;

    /**
     * @var Cart
     */
    private $cart;

    /**
     * @var PriceProvider
     */
    private $priceProvider;

    /**
     * Adds product to customers cart with user-specific price
     *
     * @param $productId
     * @return CartLine
     */
    public function addProductToCart($productId)
    {
        $price = $this->priceProvider->priceForProduct($productId, $this->customerId, $this->country);
        return $this->cart->addLine($productId, $price);
    }
}

/**
 * Simple CartLine object for persisting purposes
 */
class CartLine
{
    public $productId;
    public $price;
    public $cartId;

    function __construct($cartId, $productId, $price)
    {
        $this->cartId    = $cartId;
        $this->price     = $price;
        $this->productId = $productId;
    }
}

class Cart
{
    private $cartId;

    public function addLine($productId, $price)
    {
        return new CartLine($this->cartId, $productId, $price);
    }
}

/**
 * Provides price for specific country
 */
class PriceProvider
{
    public function priceForProduct($productId, $userId, $country)
    {
        // Logic for determining product price for customer
        // Based on available global discounts, user discounts and country
    }
}

/**
 * Command for adding product to cart
 */
class AddProductToCart
{
    public $customerId;
    public $productId;
}

/**
 * An application service to bind everything together
 */
class CustomerService
{
    public function addProductToCart(AddProductToCart $command)
    {
        /** @var Customer $customer */
        $customer = $this->customerRepository->customerOfId($command->customerId);
        $cartLine = $customer->addProductToCart($command->productId);

        $this->cartLineRepository->save($cartLine);
    }
}

Is this a correct approach? Do I violate any DDD principles here? Can I improve something?

You need an event too: AddProductToCartCommand-->ProductAddedToCartEvent — MeTitus
Just out of curiosity, Is this intended to be a learning app or a production app ? — Sudarshan

Mik378 Mik378 · Accepted Answer · 2014-08-10T14:42:10

CQRS generally involves command handler.
Command is associated to "imperative" verb.
CustomerService is too broad and so does not represent the intent of the "command".

I would change CustomerService by AddProductToCart:

class AddProductToCart
{
    public function handle(AddProductToCartCommand $command) {
      ...
    }
}

By the way, by splitting all your various functionalities into appropriate commands, you would be able to make several versions of one specific command them if you need to.

Shopping context modelling

2 Answers