private function deleteReferenceInTasks()
 {
     $contextId = $this->getId();
     $tasks = PcTaskPeer::getTasksByContextId($contextId);
     foreach ($tasks as $task) {
         $contextIdsString = $task->getContexts();
         $contextIds = PcUtils::explodeWithEmptyInputDetection(',', $contextIdsString);
         $contextIds = array_diff($contextIds, array($contextId));
         $task->setContexts(implode(',', $contextIds))->save();
     }
 }