public function set($entity, $entity_id, $created, $user_id = null)
    {
        if (!isset($user_id)) {
            $user_id = $this->user->getId(); // Current user
        }

        if ($this->exists($entity, $entity_id, $user_id)) {
            return true;
        }

        if ((GC_TIME - $created) >= $this->getLifespan()) {
            return true; // Expired and was removed
        }

        $data = array(
            'entity' => $entity,
            'user_id' => $user_id,
            'entity_id' => $entity_id
        );

        return $this->add($data);
    }