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
>
> > > --
> > > You received this message because you are subscribed
> > to the
> > > Google Groups "Google App Engine for Java" group.
> > > To post to this group, send email to google-
> > appengine-
> > > j...@googlegroups.com.
> > > To unsubscribe from this group, send email to
> > google-
> > > appengine-java+unsubscr...@googlegroups.com.
> > > For more options, visit this group at
> > > http://groups.google.com/group/google-appengine-
> > java?hl=en.
>
> > > --
>
> > > You received this message because you are subscribed to the
> > Google
> > > Groups "Google App Engine for Java" group.
> > > To post to this group, send email to google-appengine-
> > > j...@googlegroups.com.
> > > To unsubscribe from this group, send email to google-
> > appengine-java
> > > +unsubscr...@googlegroups.com.
> > > For more options, visit this group at
> > >http://groups.google.com/group/google-appengine-java?hl=en.
>
> > --
> > You received this message because you are subscribed to the
> > Google Groups "Google App Engine for Java" group.
> > To post to this group, send email to google-appengine-
> > j...@googlegroups.com.
> > To unsubscribe from this group, send email to google-
> > appengine-java+unsubscr...@googlegroups.com.
> > For more options, visit this group at
> > http://groups.google.com/group/google-appengine-java?hl=en.
>
> > --
> > You received this message because you are subscribed to the Google
> > Groups "Google App Engine for Java" group.
> > To post to this group, send email to google-appengine-
> > j...@googlegroups.com.
> > To unsubscribe from this group, send email to google-appengine-java
> > +unsubscr...@googlegroups.com.
> > For more options, visit this group at
> >http://groups.google.com/group/google-appengine-java?hl=en.
--
You received this message because you are subscribed to the Google Groups
"Google App Engine for Java" group.
To post to this group, send email to google-appengine-j...@googlegroups.com.
To unsubscribe from this group, send email to
google-appengine-java+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/google-appengine-java?hl=en.
