<?php

use Doctrine\ODM\MongoDB\DocumentManager;
use Doctrine\ORM\Event\LifecycleEventArgs;

class MyEventSubscriber
{
    public function __construct(DocumentManager $dm)
    {
        $this->dm = $dm;
    }

    public function postLoad(LifecycleEventArgs $eventArgs)
    {
        if ($eventArgs->getObject() instanceof Customer) {
            $customer = $eventArgs->getEntity();
            $em = $eventArgs->getEntityManager();
            $ordersReflProp = $em->getClassMetadata('AcmeBundle:Customer')
                ->reflClass->getProperty('orders');
            $ordersReflProp->setAccessible(true);
            $ordersReflProp->setValue(
                $customer, $this->dm->getRepository('AcmeBundle:Order')
                    ->findBy(array('customer' => $customer->getId()))
            );
        }
    }
}