class TableSortExtender

class TableSortExtender extends SelectExtender {

  /**
   * The array of fields that can be sorted by.
   */
  protected $header = array();
  public function __construct(SelectInterface $query, Connection $connection) {
    parent::__construct($query, $connection);

    // Add convenience tag to mark that this is an extended query. We have to
    // do this in the constructor to ensure that it is set before preExecute()
    // gets called.
    $this
      ->addTag('tablesort');
  }

  /**
   * Order the query based on a header array.
   *
   * @param array $header
   *   Table header array.
   *
   * @return SelectQueryInterface
   *   The called object.
   *
   * @see theme_table()
   */
  public function orderByHeader(array $header) {
    $this->header = $header;
    $ts = $this
      ->init();
    if (!empty($ts['sql'])) {

      // Based on code from db_escape_table(), but this can also contain a dot.
      $field = preg_replace('/[^A-Za-z0-9_.]+/', '', $ts['sql']);

      // Sort order can only be ASC or DESC.
      $sort = drupal_strtoupper($ts['sort']);
      $sort = in_array($sort, array(
        'ASC',
        'DESC',
      )) ? $sort : '';
      $this
        ->orderBy($field, $sort);
    }
    return $this;
  }

  /**
   * Initialize the table sort context.
   */
  protected function init() {
    $ts = $this
      ->order();
    $ts['sort'] = $this
      ->getSort();
    $ts['query'] = $this
      ->getQueryParameters();
    return $ts;
  }

  /**
   * Determine the current sort direction.
   *
   * @return
   *   The current sort direction ("asc" or "desc").
   *
   * @see tablesort_get_sort()
   */
  protected function getSort() {
    return tablesort_get_sort($this->header);
  }

  /**
   * Compose a URL query parameter array to append to table sorting requests.
   *
   * @return
   *   A URL query parameter array that consists of all components of the current
   *   page request except for those pertaining to table sorting.
   *
   * @see tablesort_get_query_parameters()
   */
  protected function getQueryParameters() {
    return tablesort_get_query_parameters();
  }

  /**
   * Determine the current sort criterion.
   *
   * @return
   *   An associative array describing the criterion, containing the keys:
   *   - "name": The localized title of the table column.
   *   - "sql": The name of the database field to sort on.
   *
   * @see tablesort_get_order()
   */
  protected function order() {
    return tablesort_get_order($this->header);
  }

}