Пример
Создание связи адреса с юзером

$address = new Address();
$address->setId(1)->setStreet("123 Example St");

$user = new User();
$user->setId(1)->setName("Harry")->setAddress($address);

$em->persist($user)->persist($address)->flush();

Получение адреса юзера

$user = $em->retrieve('User', 1);   // Only user entity retrieved
$address = $user->getAddress();     // DB call to get address made here

https://github.com/bravo3/orm