// Set of all present connection identifiers
Set<String> identifiers = new HashSet<String>();
// Set up Criteria
ConnectionExample example = new ConnectionExample();
Criteria criteria = example.createCriteria();
if(parentID != null)
criteria.andParent_idEqualTo(parentID);
else
criteria.andParent_idIsNull();
// Query connection identifiers
List<Connection> connections =
connectionDAO.selectByExample(example);
for (Connection connection : connections)