Small issue with persist() - symfony

Question

I have the following two entities:
<?php
namespace Site\AnnonceBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
use Site\UserBundle\Entity\User;
/**
* Site\AnnonceBundle\Entity\Sujet
*
* #ORM\Table()
* #ORM\Entity(repositoryClass="Site\AnnonceBundle\Entity\SujetRepository")
*/
class Sujet
{
/**
* #var integer $id
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
//Some code...
/**
*
* #ORM\ManyToOne(targetEntity="Site\UserBundle\Entity\User")
*/
private $user;
//getter/setter....
user Entity(FOSUserBundle) :
<?php
namespace Site\UserBundle\Entity;
use FOS\UserBundle\Entity\User as BaseUser;
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity
* #ORM\Table()
*
*/
class User extends BaseUser{
/**
* #ORM\Id
* #ORM\Column(type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
public function getId() {
return $this->id;
}
}
when I created a "Sujet", I made(in SujetController.php):
$em = $this->getDoctrine()->getEntityManager();
$sujet->setResolu(false);
$em->persist($sujet);
$em->flush();
its works, But the inserted "Sujet" in the database refer to user null... so in the second version i made this:
$em = $this->getDoctrine()->getEntityManager();
$sujet->setResolu(false);
$sujet->setUser(new User($this->get('session')->get('user_id'))) ;//the user is already in the DB
$em->persist($sujet);
$em->flush();
but i get this error:
A new entity was found through the relationship 'Site\AnnonceBundle\Entity\Sujet#user' that was not configured to cascade persist operations for entity: . Explicitly persist the new entity or configure cascading persist operations on the relationship. If you cannot find out which entity causes the problem implement 'Site\UserBundle\Entity\User#__toString()' to get a clue.
I do not understand, I have already worked with another ORM (JPA) and it works in that way ...
how to tell "Sujet" about what is related to an entity already existing in database?
(sorry if my english is bad)
EDIT : its worked for me :
$user = $this->get('security.context')->getToken()->getUser();
$sujet->setUser($user);
$em->persist($sujet);
$em->flush();

Answer 1

Just in case, the error came from the fact you created a new User and linked it to the sujet without persisting it (as there is no cascade, the entity was linked to a none persisted entity, resulting in the error).
Your edit suggests you found a way to get the current User (this one is persisted, unlike the "new User") you made before.
You could also have done :
$repository = $this->getDoctrine()
->getEntityManager()
->getRepository('YourBundle:User');
$user = $repository->find($iduser);
$sujet->setUser($user);
It would have been a good solution if you wanted to make the edit "for another user".