@Override
  public void registerHostName(long hostRequestId, String hostName) {
    TopologyHostRequestEntity entity = hostRequestDAO.findById(hostRequestId);
    if (entity.getHostName() == null) {
      entity.setHostName(hostName);
      hostRequestDAO.merge(entity);
    }
  }
Implementation which uses Ambari Database DAO and Entity objects for persistence
of topology related information.
ambari-server/src/main/java/org/apache/ambari/server/topology/PersistedStateImpl.java