public FriendDTO updateFriend(FriendDTO friendDTO) {
PersistenceManager pm = PMF.getTxnPm();
if (friendDTO.getId() == null) { // create new Friend
Friend newFriend = addFriend(friendDTO);
return newFriend.toDTO();
}
// otherwise, do an update of an existing Friend.
// do this operation under transactional control
Friend friend = null;