gistfile1.php

$user = $em->find("Entities\User", $idUser);

$query = $em->createQuery('SELECT messages, responses FROM Entities\Message messages JOIN messages.responses JOIN messages.user user WHERE user.id = :id_user);
$query->setParameter("id_user", $user->getId());


$messages = $query->getResult();

foreach ($messages as $message) {
  $responses = $message->getResponses(); //Entities\Message
}