Can't save the relation in a self-referencing entity - symfony

Question

Im tying to add communication parts to a rootCommunication in my data-fixture, there is no error, but only just NULL in the database field 'root_communication_id'. Why?
Parts of my Model 'Communication'
/**
* Communication
*
* #ORM\Table(name="communication")
* #ORM\Entity(repositoryClass="Mother\BaseBundle\Entity\Repository\CommunicationRepository")
*/
class Communication
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="message", type="text", nullable=true)
*/
private $message;
/**
* #ORM\ManyToOne(targetEntity="Communication", inversedBy="childrenCommunication", cascade={"persist"})
* #ORM\JoinColumn(name="root_communication_id", referencedColumnName="id", nullable=true)
*
*/
private $rootCommunication;
/**
* #ORM\OneToMany(targetEntity="Communication", mappedBy="rootCommunication")
*
*/
private $childrenCommunication;
}
In a first data-fixture i added three communications to the database, in this secound fixture i add the childrenCommunication to the rootCommunication.
/**
* {#inheritDoc}
*/
public function load( ObjectManager $manager ){
$contentRepo = $this->container->get('doctrine')->getManager()->getRepository('MotherBaseBundle:Communication');
$communication1 = $contentRepo->find( $this->getReference('communication1')->getId() );
$communication1->addChildrenCommunication( $this->getReference('communication2') );
$communication1->addChildrenCommunication( $this->getReference('communication3') );
$manager->persist( $communication1 );
$manager->flush();
}

Answer 1

I assume you are not setting the rootCommunication when you are adding the child.
You should add an auto setter to the add method, like..
public function addChildrenCommunication(CommunicationInterface $communication)
{
if (!$this->childrenCommunication->contains($communication)) {
$this->childrenCommunication->add($communication);
$communication->setRootCommunication($this);
}
return $this;
}
.. and the same for the remove..