Reference ID not updated with Doctrine association - php

Question

There is probably something I did understand with Doctrine association.
I have a first class :
class FitComments
{
/**
* #var integer
*
* #ORM\Column(name="ID", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="SEQUENCE")
* #ORM\SequenceGenerator(sequenceName="SEQ_FIT_COMMENTS", allocationSize=1, initialValue=1)
*/
private $id;
/**
*
* #ORM\OneToMany(targetEntity="FitCommentsId",mappedBy="comments",cascade={"persist"})
*
*/
private $elements;
/****/
public function __construct()
{
$this->elements=new ArrayCollection();
}
public function getElements()
{
return $this->elements;
}
....
}
And a another Class, the list of elements ID that the comments is link.
/**
* FitCommentsId
* #ORM\Entity
*/
class FitCommentsId
{
/**
* #var integer
*
* #ORM\Column(name="ID", type="integer", nullable=false)
* #ORM\Id
* #ORM\GeneratedValue(strategy="SEQUENCE")
* #ORM\SequenceGenerator(sequenceName="SEQ_FIT_COMMENTS_ID", allocationSize=1, initialValue=1)
*/
private $id;
/**
*
* #ORM\ManyToOne(targetEntity="FitComments",inversedBy="elements")
* #ORM\JoinColumn(name="COMMENTS_ID",referencedColumnName="ID")
*/
private $comments;
....
}
I use :
$comments=new FitComment();
$commentId=new FitCommentId();
....
$comments->getElements()->add($commentId);
....
$entityManager->persist($comment);
$entityManager->flush();
But I have a error. $commentId->comments is null. It must be filled with $comment->id normally.
If I must filled manually $commentId->comments, association is not very usefull.
Perhaps I don't understand mechanism.
Note : the SGDB is Oracle.

Answer 1

Try persisting the $commentId also like this:
$comment = new FitComment();
$commentId = new FitCommentId();
....
$comment->getElements()->add($commentId);
....
$entityManager->persist($commentId);
$entityManager->persist($comment);
$entityManager->flush();

Answer 2

No I can't do a 'persist' to $commentId first, because 'persist' to $comment class initiate Oracle sequence for the Id of $comments. (I'm not sure it's very clean what I say....)
'commentID->comments' is link to 'comment->id', and is not null.
I must create $comment at first, and after, create the $commentId.
I know that Doctrine use Sequence before saving record, in persist command. Perhaps I can do a persist without flush at first, and at the end of $commentId recording, do a flush.