protected function addSortQuery($query)
  {
    if (array(null, null) == ($sort = $this->getSort()))
    {
      return;
    }

    if (!in_array(strtolower($sort[1]), array('asc', 'desc')))
    {
      $sort[1] = 'asc';
    }

    $query->addOrderBy($sort[0] . ' ' . $sort[1]);
  }

  protected function getSort()
  {
    if (null !== $sort = $this->getUser()->getAttribute('