On Wednesday 12 November 2008 00:44, xor wrote:
>
> > -----Original Message-----
> > From: devl-bounces at freenetproject.org
> > > @@ -178,8 +178,20 @@
> > > public synchronized Iterator<FMSMessage> threadIterator(final
> > FMSOwnIdentity identity) {
> > > return new Iterator<FMSMessage>() {
> > > private final FMSOwnIdentity mIdentity
> > = identity;
> > > - private Iterator<FMSMessage> iter =
> > self.mThreads.iterator();
> > > - private FMSMessage next =
> > iter.hasNext() ? iter.next() : null;
> > > + private final ObjectSet<FMSMessage> mMessages;
> > > + private final Iterator<FMSMessage> iter;
> > > + private FMSMessage next;
> > > +
> > > + {
> > > + Query q = db.query();
> > > + q.constrain(FMSMessage.class);
> > > +
> > > q.descend("mBoards").constrain(mName); /* FIXME: mBoards is an array.
> > > Does constrain() check whether it contains the element mName? */
> >
> > No.
>
> This is bad news! It means that we will have to store a per board message
> list in some way. Any ideas on how to do it efficiently using db4o as much
> as possible?
Hmmm... I may be wrong here... I dunno how indexes would be used in such a
case, I think if you use QBE (and therefore presumably constrain) you can do
it...
>
> Well actually its good news: Even if that query was possible, it
> would not be efficient anyway.
Dunno whether it uses an index for such things.
> The only efficient way of retrieving
> messages per-board is to store a per-board list of messages of course.
Or use a tag object (struct with the board and the message) to connect them.
> As you know I had done that with LinkedLists and Hashtables in the past
> but changed it to this simple db4o query for the sake of using db4o.
These will have to loaded in their entirety, but that's probably acceptable in
this case - the number of messages on a board won't be vast.
>
> > > + q.descend("mParentURI").constrain(null);
> >
> > You should add .identity(). However, in my experience
> > constraining to null doesn't work, or works but pulls in
> > every object rather than using the index.
>
> This sucks. In my current design of the FMSMessage class, a thread is
> defined by not having a parent URI. It means that I will have to
> add booleans everywhere where I use null as a special information.
>
> Is this a db4o bug?
It works but it doesn't use the index, in my experience:
http://tracker.db4o.com/browse/COR-1446
>
> >
> > > + q.orderDescending();
> >
> > Descending on which field?
>
> I had already fixed that. We sort by date.
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