public function onPreDelete(StorageEvent $event)
    {
        $entity = $event->getContent();
        if (!$entity instanceof Entity\Content) {
            return;
        }
        $taxonomies = $entity->getTaxonomy();
        if ($taxonomies instanceof Collection\Taxonomy) {
            $repo = $this->em->getRepository(Entity\Taxonomy::class);
            foreach ($taxonomies as $taxonomy) {
                $repo->delete($taxonomy);
            }
        }
        $relations = $entity->getRelation();
        if ($relations instanceof Collection\Relations) {
            $repo = $this->em->getRepository(Entity\Relations::class);
            foreach ($relations as $relation) {
                $repo->delete($relation);
            }
        }
    }