q.descend("mMessage").constrain(message).identity();
q.descend("mBoard").constrain(this).identity();
ObjectSet<DownloadedMessageLink> messageLinks = new Persistent.InitializingObjectSet<Board.DownloadedMessageLink>(mFreetalk, q);
switch(messageLinks.size()) {
case 0: throw new NoSuchMessageException(message.getID());
case 1: return messageLinks.next();
default: throw new DuplicateMessageException(message.getID());
}
}