public function save(Indexation $index)
    {
        $existing = $this->find([
            '_content' => $index->getContent(),
            '_field' => $index->getField(),
        ]);

        if (null === $existing) {
            $existing = $index;
            $this->getEntityManager()->persist($existing);
        } else {
            $existing->setValue($index->getValue());
        }

        $metadata = $this->getEntityManager()->getClassMetadata('BackBee\ClassContent\Indexation');
        $this->getEntityManager()
                ->getUnitOfWork()
                ->computeChangeSet($metadata, $existing);
    }