Doctrine2 - OneToMany/ManyToOne Bidirectional not working - symfony

Question

Hi everyone and thanks for help,
I'm currently dealing with a problem while I want to make an OneToMany/ManyToOne Bidirectional Relationship with Doctrine2 (& Symfony2).
Here are my two classes : User (which extends FOSUser) and collection which represents a collection of videos.
Of course, a user can have several collections, but a collection is only related to one user.
/* COLLECTION */
namespace Com\ComBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
/**
* Com\ComBundle\Entity\Collection
*
* #ORM\Table(name="collection")
* #ORM\HasLifecycleCallbacks
*/
class Collection
{
/**
* #var integer $id
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #ORM\ManyToOne(targetEntity="Com\UserBundle\Entity\User", inversedBy="collections")
* #ORM\JoinColumn(nullable=false)
*/
private $user;
/**
* Set user
*
* #param Com\UserBundle\Entity\User $user
* #return Collection
*/
public function setUser(\Com\UserBundle\Entity\User $user) {
$this->user = $user;
return $this;
}
/**
* Get user
*
* #return Com\UserBundle\Entity\User User
*/
public function getUser() {
return $this->user;
}
}
And user,
/* USER */
namespace Com\UserBundle\Entity;
use FOS\UserBundle\Entity\User as BaseUser;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
/**
* #ORM\Entity
* #ORM\Table(name="user")
*/
class User extends BaseUser
{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/*
* #ORM\OneToMany(targetEntity="Com\ComBundle\Entity\Collection", mappedBy="user")
*/
private $collections;
public function __construct()
{
parent::__construct();
$this->collections = \Doctrine\Common\Collections\ArrayCollection();
}
}
When I use the doctrine:generate:entities command, it does not generate the methods relative to $collections (get/add/remove), and even if I wrote it myself, it does not work.
getCollections() return NULL for example.
What am I missing in this code ?