static public function create($generatorType)
    {
        switch ($generatorType) {
            case ClassMetadata::IDGENERATOR_ASSIGNED:
                $instance = new AssignedIdGenerator();
                break;
            case ClassMetadata::IDGENERATOR_UUID:
                $instance = new CouchUUIDGenerator();
                break;
            default:
                throw new \Exception("ID Generator does not exist!");
        }
        return $instance;
    }
static public function create($generatorType)
    {
        switch ($generatorType) {
            case ClassMetadata::IDGENERATOR_ASSIGNED:
                $instance = new AssignedIdGenerator();
                break;
            case ClassMetadata::IDGENERATOR_UUID:
                $instance = new CouchUUIDGenerator();
                break;
            default:
                throw new \Exception("ID Generator does not exist!");
        }
        return $instance;
    }
@param int $generatorType

@return IdGenerator
@throws \Exception