protected function addEntity($type, $id, Entity\Content $owner)
    {
        $newEntity = new Entity\Relations([
            'from_contenttype' => (string) $owner->getContenttype(),
            'from_id'          => $owner->getId(),
            'to_contenttype'   => $type,
            'to_id'            => $id,
        ]);
        $this->add($newEntity);
    }