Save Cascade many To many Symfony 2 - symfony

Question

I'm following the Documentation About Authentication. Now I want implement Role
This is my entities
User.php
/**
* #var \Doctrine\Common\Collections\Collection
*
* #ORM\ManyToMany(targetEntity="Role", inversedBy="users", cascade={"all"})
* #ORM\JoinTable(name="user_role",
* joinColumns={
* #ORM\JoinColumn(name="user_id", referencedColumnName="id")
* },
* inverseJoinColumns={
* #ORM\JoinColumn(name="role_id", referencedColumnName="id")
* }
* )
*/
private $roles;
public function __construct () {
$this->roles = new ArrayCollection();
}
public function getRoles () {
return $this->roles->toArray();
}
public function getRoles2 () {
return $this->roles;
}
Than i Have three tables
users user_role role
roles
<?php
namespace ADV\UserBundle\Entity;
use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\Mapping as ORM;
/**
* Role
*
* #ORM\Table(name="role")
* #ORM\Entity(repositoryClass="ADV\UserBundle\Entity\RoleRepository")
*/
class Role
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="name", type="string", length=30)
*/
private $name;
/**
* #var string
*
* #ORM\Column(name="role", type="string", length=20)
*/
private $role;
/**
* #ORM\ManyToMany(targetEntity="User", mappedBy="roles")
*/
private $users;
public function __construct()
{
$this->users = new ArrayCollection();
}
/**
* Get id
*
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* Set name
*
* #param string $name
* #return Role
*/
public function setName($name)
{
$this->name = $name;
return $this;
}
/**
* Get name
*
* #return string
*/
public function getName()
{
return $this->name;
}
/**
* Set role
*
* #param string $role
* #return Role
*/
public function setRole($role)
{
$this->role = $role;
return $this;
}
/**
* Get role
*
* #return string
*/
public function getRole()
{
return $this->role;
}
/**
* Add users
*
* #param \ADV\UserBundle\Entity\User $users
* #return Role
*/
public function addUser(\ADV\UserBundle\Entity\User $users)
{
$this->users[] = $users;
return $this;
}
/**
* Remove users
*
* #param \ADV\UserBundle\Entity\User $users
*/
public function removeUser(\ADV\UserBundle\Entity\User $users)
{
$this->users->removeElement($users);
}
/**
* Get users
*
* #return \Doctrine\Common\Collections\Collection
*/
public function getUsers()
{
return $this->users;
}
}
I create two form, userType and Roletype, and UserType "embed" the roleType
->add('roles', 'collection', array(
'type' => new RoleType()
))
My Controller:
public function registrationAction (Request $request) {
$user = new User();
$role = new Role();
$user->getRoles2()->add($role);
$form = $this->createForm(new UserType(), $user);
$form->handleRequest($request);
if ($form->isValid()) {
$em = $this->getEm();
try {
$em->beginTransaction();
$factory = $this->get('security.encoder_factory');
$encoder = $factory->getEncoder($user);
$user->setSalt(md5(time()));
$password = $encoder->encodePassword($user->getPassword(), $user->getSalt());
$user->setPassword($password);
$em->persist($user);
$em->flush();
$em->commit();
} catch (\Exception $e) {
$em->rollback();
}
}
return array(
'form' => $form->createView()
);
}
I have the Right Form
A new entity was found through the relationship
'ADV\UserBundle\Entity\User#roles' that was not configured to cascade
persist operations for entity: ROLE_WRITER. To solve this issue:
Either explicitly call EntityManager#persist() on this unknown entity
or configure cascade persist this association in the mapping for
example #ManyToOne(..,cascade={"persist"}).
But I want to use ManyToMay, and if I add cascade, each time that I create a new User, create also a new Role related