/**
  * Retrieve all editions for a specific project
  *
  * @param integer $project_id
  * 
  * @return array
  */
 public static function getAllByProjectID($project_id)
 {
     if (self::$_editions === null) {
         self::$_editions = array();
     }
     if (!array_key_exists($project_id, self::$_editions)) {
         self::$_editions[$project_id] = array();
         if ($res = B2DB::getTable('TBGEditionsTable')->getByProjectID($project_id)) {
             while ($row = $res->getNextRow()) {
                 $edition = TBGContext::factory()->TBGEdition($row->get(TBGEditionsTable::ID), $row);
                 self::$_editions[$project_id][$edition->getID()] = $edition;
             }
         }
     }
     return self::$_editions[$project_id];
 }