public function delete()
 {
     global $ilDB;
     $query = 'DELETE FROM cal_ch_group ' . 'WHERE grp_id = ' . $ilDB->quote($this->getGroupId(), 'integer');
     $ilDB->manipulate($query);
     include_once './Services/Booking/classes/class.ilBookingEntry.php';
     ilBookingEntry::resetGroup($this->getGroupId());
 }