If i remove $this->em->flush($conceptNew); i get: Entity of type Ukratio\TrouveToutBundle\Entity\ConceptConcept has identity through a foreign entity Ukratio\TrouveToutBundle\Entity\Concept, however this entity has no identity itself. You have to call EntityManager#persist() on the related entity and make sure that an identifier was generated be…

Concept.php

<?php

namespace Ukratio\TrouveToutBundle\Entity;

use /*all the uses*/


/**
 * Ukratio\TrouveToutBundle\Entity\Concept
 *
 * @ORM\Table()
 * @ORM\Entity(repositoryClass="Ukratio\TrouveToutBundle\Entity\ConceptRepository")
 * @UniqueEntity("name")
 */
class Concept
{

    /**
     * @var ArrayCollection
     *
     * @ORM\OneToMany(targetEntity="Ukratio\TrouveToutBundle\Entity\ConceptConcept", mappedBy="moreSpecific", cascade={"persist"}, orphanRemoval=true)
     */
    private $moreGeneralConceptConcepts;

    /**
     * @var ArrayCollection
     *
     * @ORM\OneToMany(targetEntity="Ukratio\TrouveToutBundle\Entity\ConceptConcept", mappedBy="moreGeneral", cascade={"persist"}, orphanRemoval=true)
     */
    private $moreSpecificConceptConcepts;

    
    public function __construct()
    {
	$this->moreGeneralConceptConcepts = new ArrayCollection();
	$this->moreSpecificConceptConcepts = new ArrayCollection();

    }

    /**
     * Get id
     *
     * @return integer 
     */
    public function getId()
    {
        return $this->id;
    }


    /**
     * Add moreGeneralConceptConcepts
     *
     * @param \Ukratio\TrouveToutBundle\Entity\ConceptConcept $moreGeneralConceptConcepts
     * @return ConceptConcept
     *
     */
    public function addMoreGeneralConceptConcept(ConceptConcept $moreGeneralConceptConcept)
    {
        $moreGeneralConceptConcept->setMoreSpecific($this);
        $this->moreGeneralConceptConcepts[] = $moreGeneralConceptConcept;
        return $this;
    }

    public function removeMoreGeneralConceptConcept(ConceptConcept $moreGeneralConceptConcept)
    {
        $this->moreGeneralConceptConcepts->removeElement($moreGeneralConceptConcept);
    }

    public function removeMoreSpecificConceptConcept(ConceptConcept $moreSpecificConceptConcept)
    {
        $this->moreSpecificConceptConcepts->removeElement($moreSpecificConceptConcept);
    }


    /**
     * Get moreGeneralConceptConcepts
     *
     * @return \Doctrine\Common\Collections\Collection
     *
     */
    public function getMoreGeneralConceptConcepts()
    {
        return $this->moreGeneralConceptConcepts;
    }
}

ConceptConcept.php

<?php

namespace Ukratio\TrouveToutBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Ukratio\TrouveToutBundle\Entity\Concept;

/**
 * ConceptConcept
 *
 * @ORM\Table()
 * @ORM\Entity
 */
class ConceptConcept
{

    /**
     * @var Ukratio\TrouveToutBundle\Entity\Concept
     *
     * @ORM\Id
     * @ORM\ManyToOne(targetEntity="Ukratio\TrouveToutBundle\Entity\Concept", inversedBy="moreSpecificConcepts")
     */
    private $moreGeneral;

    /**
     * @var Ukratio\TrouveToutBundle\Entity\Concept
     *
     * @ORM\Id
     * @ORM\ManyToOne(targetEntity="Ukratio\TrouveToutBundle\Entity\Concept", inversedBy="moreGeneralConcepts")
     */
    private $moreSpecific;


    public function linkConcepts(Concept $moreSpecific, Concept $moreGeneral)
    {
        $this->setMoreGeneral($moreGeneral);
        $this->setMoreSpecific($moreSpecific);
    }

    /**
     * Set moreGeneral
     *
     * @param \Ukratio\TrouveToutBundle\Entity\Concept $moreGeneral
     * @return ConceptConcept
     *
     * @codeCoverageIgnore
     */
    public function setMoreGeneral(Concept $moreGeneral)
    {
        $this->moreGeneral = $moreGeneral;
    
        return $this;
    }

    /**
     * Get moreGeneral
     *
     * @return \Ukratio\TrouveToutBundle\Entity\Concept
     *
     * @codeCoverageIgnore
     */
    public function getMoreGeneral()
    {
        return $this->moreGeneral;
    }

    /**
     * Set moreSpecific
     *
     * @param \Ukratio\TrouveToutBundle\Entity\Concept $moreSpecific
     * @return ConceptConcept
     *
     * @codeCoverageIgnore
     */
    public function setMoreSpecific(Concept $moreSpecific)
    {
        $this->moreSpecific = $moreSpecific;
        
        return $this;
    }

    /**
     * Get moreSpecific
     *
     * @return \Ukratio\TrouveToutBundle\Entity\Concept
     *
     * @codeCoverageIgnore
     */
    public function getMoreSpecific()
    {
        return $this->moreSpecific;
    }

}

controlleur.php

public function testAction(Request $request)
{
        $this->em = $this->getDoctrine()->getManager();
        $this->repo = $this->em->getRepository('TrouveToutBundle:Concept');

        $conceptMouchoir = $this->repo->findOneByName('mouchoir');
        $conceptNew = new Concept();
        $conceptNew->setName('conceptNew');
        $this->em->persist($conceptNew);
        $this->em->flush($conceptNew);

        $conceptConcept = new ConceptConcept();
        $conceptConcept->setMoreGeneral($conceptMouchoir);
        $conceptNew->addMoreGeneralConceptConcept($conceptConcept);

        $this->em->persist($conceptNew);
        $this->em->flush($conceptNew);

        return new Response("ok");
}

If i remove "$this->em->flush($conceptNew); " in controlleur.php line 10, i get:

Entity of type Ukratio\TrouveToutBundle\Entity\ConceptConcept has identity through a foreign entity Ukratio\TrouveToutBundle\Entity\Concept, however this entity has no identity itself. You have to call EntityManager#persist() on the related entity and make sure that an identifier was generated before trying to persist 'Ukratio\TrouveToutBundle\Entity\ConceptConcept'. In case of Post Insert ID Generation (such as MySQL Auto-Increment or PostgreSQL SERIAL) this means you have to call EntityManager#flush() between both persist operations.