Question

I am building .net application using nhibernate for mapping data to entities. I am still newbie in object oriented programming and now I have this question:

I have entities such as Customer, Order, Product etc. I can fetch objects by nhibernate from data from database and list customers etc. But what if I want to list customers with its order totals? These are not data for customer entity, nor order entity. How to fetch and list such combined data? Should they have its own data transfer object or is here better way how to do this?

Answer 1

Have an additional entity, CustomerList, which will hold the Customer object.

The CustomerList will have a method to sort the list according to the order totals, which will be done by accessing each memeber’s order totals and comparing them.

In PHP, I would do something like so (That is only an example, in real code there may be other things you’ll need to take into account).

<?php

/**
 * Describe a single customer object
 */
class Customer {

    /** @var Order[] List of orders */
    private $orders = array();

    /**
     * Add an order to the order list.
     *
     * @param Order $order
     */
    public function addOrder(Order $order) {
        if (!in_array($order, $this->orders, true)) {
            $this->orders[] = $order;
        }
    }

    /**
     * Get an order by numeric index.
     *
     * @param int $index
     *
     * @return Order
     */
    public function getOrder($index) {
        return $this->orders[$index];
    }

    /**
     * Get total number of orders for customer.
     *
     * @return int
     */
    public function getOrdersTotal() {
        return count($this->orders);
    }
}

/**
 * Describe a single order.
 * I didn't include any information here because it's not relevant.
 */
class Order {

}

/**
 * Describe a list of customers.
 */
class CustomerList {

    /** @var Customer[] List of customers */
    private $customers;

    /**
     * Add a customer to the list
     *
     * @param Customer $customer
     */
    public function addCustomer(Customer $customer) {
        $this->customers[] = $customer;
    }

    /**
     * The sorting function.
     * Compare the orders total and return 1/0/-1 accordingly.
     *
     * @param Customer $a
     * @param Customer $b
     *
     * @return int
     */
    public function sort($a, $b) {
        if ($a->getOrdersTotal() === $b->getOrdersTotal()) {
            return 0;
        }
        return ($a->getOrdersTotal() > $b->getOrdersTotal()) ? 1 : -1;
    }

    /**
     * Call the sorting function on the customer list
     */
    public function sortCustomers() {
        usort($this->customers, array($this, "sort"));
    }

    /**
     * Return the full customer array.
     *
     * @return Customer[]
     */
    public function getCustomers() {
        return $this->customers;
    }
}

//Instantiation
$cList = new CustomerList();

$customer1 = new Customer();
$customer2 = new Customer();
$customer3 = new Customer();

$order1 = new Order();
$order2 = new Order();
$order3 = new Order();
$order4 = new Order();
$order5 = new Order();
$order6 = new Order();

$customer1->addOrder($order1);
$customer1->addOrder($order2);

$customer2->addOrder($order3);

$customer3->addOrder($order4);
$customer3->addOrder($order5);
$customer3->addOrder($order6);

$cList->addCustomer($customer1);
$cList->addCustomer($customer2);
$cList->addCustomer($customer3);

//List customers before sorting
var_dump($cList->getCustomers());

$cList->sortCustomers();

//List customers after sorting
var_dump($cList->getCustomers());