/**
   * @todo.
   */
  public function pack($exportable) {
    $data = array();

    foreach ($this->schema['fields'] as $field => $info) {
      if (isset($exportable->{$field})) {
        $data[$field] = $exportable->{$field};
      }
      else {
        $data[$field] = !empty($info['default']) ? $info['default'] : NULL;
      }
    }

    return $data;
  }