/**
  * @return Array of Tracker
  */
 public function getPossibleChildren(Tracker_Hierarchy_HierarchicalTracker $tracker)
 {
     $project_trackers = $this->getProjectTrackers($tracker->getProject());
     $ids_to_remove = $this->dao->searchAncestorIds($tracker->getId());
     $ids_to_remove[] = $tracker->getId();
     $project_trackers = $this->removeIdsFromTrackerList($project_trackers, $ids_to_remove);
     return $project_trackers;
 }
 private function getTrackersNotInHierachy()
 {
     $trackers_not_in_hierarchy = array();
     EventManager::instance()->processEvent(TRACKER_EVENT_TRACKERS_CANNOT_USE_IN_HIERARCHY, array('project' => $this->tracker->getProject(), 'result' => &$trackers_not_in_hierarchy));
     return $trackers_not_in_hierarchy;
 }