[doctrine] Update multiple database rows using Update statement

When you have to update multiple entities, retrieving them all from the database and iterating over ORM entities is known as a bad practice.

You should never do like:

<?php

$friend = $em->getReference('Octivi\Entity\User', $friendId);
$users = $this->findAll();

foreach ($users as $user) {
    $user->setFriend($friend);
    $em->persist($user);
}

$em->flush();

Instead, you should rely on the UPDATE query:

<?php 
$qb->update('Octivi:User', 'u')
    ->set('u.friend', $friendId)
    ->getQuery()->execute();

Thanks to it, we only execute one SQL UPDATE statement instead of N-updates for each User entity.