public function getSousCategories(\Id2i\Core\NodeBundle\Entity\Node $parent)
 {
     return $this->_em->createQueryBuilder()->select(array('n'))->from('NodeBundle:Node', 'n')->where('n.parent = :parent AND n.root = :root AND n.lft > :parentLft AND n.rgt < :parentRgt')->setParameters(array('parent' => $parent, 'root' => $parent->getRoot(), 'parentLft' => $parent->getLft(), 'parentRgt' => $parent->getRgt()));
 }