Lazyloading in PHP

lazyload.php

<?php

abstract class Loader
{
	abstract public function load();
}

class PaymentLoader extends Loader
{
	protected $id;
	public function __construct($id) { $this->id = $id; }
	
	public function load()
	{
		if ($this->id == 123)
		{
			return array(
				'amount' => 100,
				'customer' => CustomerRepository::findById(5),
			);
		}
	}
}

class CustomerLoader extends Loader
{
	protected $id;
	public function __construct($id) { $this->id = $id; }
	
	public function load()
	{
		if ($this->id == 5)
		{
			return array(
				'id' => 5,
				'name' => 'John Doe',
			);
		}
	}
}


class LazyObject
{
	protected $fields;
	protected $loader;

	public function __get($field)
	{
		if (!isset($this->fields) && isset($this->loader))
		{
			$this->fields = $this->loader->load();
		}
		
		return $this->fields[$field];
	}
	
	public function setLoader(Loader $loader)
	{
		$this->loader = $loader;
	}
}


class Customer extends LazyObject
{
}

class Payment extends LazyObject
{
}


class PaymentRepository
{
	public static function findById($id)
	{
		$payment = new Payment;
		$payment->setLoader(new PaymentLoader($id));
		return $payment;
	}
}

class CustomerRepository
{
	public static function findById($id)
	{
		$customer = new Customer;
		$customer->setLoader(new CustomerLoader($id));
		return $customer;
	}
}


function pre($x)
{
	echo '<pre>';
	print_r($x);
	echo '</pre>';
}

$payment = PaymentRepository::findById(123);
pre($payment);
echo 'Amount: ', $payment->amount, '<br>';
pre($payment);
echo 'Customer name: ', $payment->customer->name, '<br>';
pre($payment);