Please see the answer i sent out yesterday for a proper solution.
Duong BaTien
DBGROUPS and BudhNet
On Sat, 2010-01-30 at 01:14 -0800, digitalsam007 wrote:
> I failed to make this code work. It seems that the MessageIndex object
> is not getting persisted when i call tx.commit().
>
> Any help in this regard will be appreciated.
>
> Thanks
>
> On Jan 17, 12:26 am, Duong BaTien <duong.bat...@gmail.com> wrote:
> > Hi:
> >
> > Following is my sketch for the Message and MessageIndex. Please advise
> > and if possible, sketch out the Java version of set intersection from
> > the presentation. Have not time to try anything yet; but the design is
> > very significant for proper data modeling. The JDO version of the
> > presentation uses query.setFilter("receivers == 'foo'") which i do not
> > see in the API.
> >
> > public class MessageIndex { // create MessageIndex to the parent Message
> > private Key parent; private String keyKind; private long id;
> >
> > @PrimaryKey
> > @Persistent(ValueStrategy = IdGeneratorStrategy.IDENTITY)
> > private KeyFactory.createKey(parent, keyKind, id) key;
> >
> > @Persistent private List<String> receivers;
> >
> > // constructor to create MessageIndex linked to Message
> > public MessageIndex(Key parent, String keyKind, long id) {
> > this.parent = parent; this.keyKind = keyKind; this id = id;
> >
> > }
> >
> > public class Message {
> > @PrimaryKey
> > @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> > private Key key
> >
> > @Persistent private String sender;
> > @Persistent private String body;
> >
> > // a user create a message to a list of receivers
> > public static Message createMessage(String userId, String body,
> > List<String> receivers) {
> > tx.begin()
> > this.body = body;
> > MessageIndex index = new MessageIndex(key, key,getKind(), key.getId
> > ());
> > index.setReceivers(receivers);
> > tx.commit();
> > }
> >
> > // query to get all messages sent to a user "foo"
> > public List<Message> getMessagesSentToUserId(String userId) {
> > List<Message> results = null
> > tx.begin();
> > Query q = pm.newQuery(MessageIndex.class);
> > q.addFilter("receivers", Query.FilterOperator.EQUAL, "foo");
> > q.setKeyOnly();
> > // query the Message for all messages filtered by parent of
> > MessageIndex key
> > Query query = pm.newQuery(Message.class);
> > query.addFilter("key", Query.FilterOperator.EQUAL, "q.execute
> > ().getParent()");
> > results = (List<Message>) query.execute();
> > tx.commit();
> > }
> >
> > }
> >
> > Thanks
> > Duong BaTien
> > DBGROUPS and BudhNet
> >
> > On Wed, 2010-01-13 at 16:26 -0800, Jason (Google) wrote:
> > > It's been awhile since I've seen this video, so I'll have to go back
> > > to re-watch it in order to answer your question completely, but I'd be
> > > interested in seeing what you've sketched out so far and happy to give
> > > you my feedback on it.
> >
> > > - Jason
> >
> > > On Tue, Jan 12, 2010 at 3:52 PM, Duong BaTien <duong.bat...@gmail.com>
> > > wrote:
> > > Hi Jason, the author Brett Slatkin and others:
> >
> > > 1) For the list property, the video shows simple example of
> > > standard 1:n
> > > Message Receivers in python and Java. It then demonstrates a
> > > very
> > > efficient technique of Message and MessageIndex with the query
> > > of
> > > MessageIndex in python (NO Java from then on). I look at both
> > > the low
> > > level datastore with Query.setKeyOnly() and the query "select
> > > id from"
> > > to get the results of List<Key>, then go through the loop to
> > > get the
> > > receivers. I may miss something, since the python code looks
> > > so clean.
> > > But once you are in any environment, it is very expensive to
> > > switch.
> > > This technique has major impact in data modeling.
> >
> > > 2) Again for the set intersection, the python code looks so
> > > clean. I
> > > roughly sketch what need to be done on the Java side with
> > > either low
> > > level of datastore or with JDO. It is still not elegant as the
> > > shown
> > > codes. The demos are also in python. Again, the technique of
> > > merge join
> > > will have very significant impact on data modeling that GAE
> > > may surpass
> > > other platforms.
> >
> > > Haven't put enough time in it yet, I wonder if any one has
> > > worked out
> > > the demos in Java and suggested best practices in data
> > > modeling for a
> > > complex large application. The job Brett Slatkin sets out to
> > > do has not
> > > completed without the Java codes since GAE now supports Java.
> >
> > > Thanks
> > > Duong BaTien
> > > DBGROUPS and BudhNet
> >
> > > On Tue, 2010-01-12 at 14:13 -0800, Jason (Google) wrote:
> > > > Can you be more specific about what you're trying to
> > > accomplish so we
> > > > don't have to search through the video to find what you're
> > > looking
> > > > for? Or, at least provide a timeline reference that we can
> > > refer to in
> > > > the video. :)
> >
> > > > Thanks,
> > > > - Jason
> >
> > > > On Mon, Jan 11, 2010 at 7:29 AM, Duong BaTien
> > > <duong.bat...@gmail.com>
> > > > wrote:
> > > > Hi:
> >
> > > > Is there any blog and/or note to apply list
> > > properties and
> > > > merge-join in
> > > > python as in the following talk and demos
> >
> > >
> > > http://code.google.com/events/io/2009/sessions/BuildingScalableComple...using
> > > Java and JDO?
> >
> > > > Thanks
> > > > Duong BaTien
> > > > DBGROUPS and BudhNet
> >
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