protected function getHydrator($type)
    {
        $hydrator = isset($this->config[$type]['hydrator'])
                  ? $this->config[$type]['hydrator']
                  : new EntityHydrator();
        
        if (is_string($hydrator)) {
            $this->config[$type]['hydrator'] = $hydrator = new $hydrator();
        }
        return $hydrator;
    }