I'm thinking of something like a "tips and tricks" section that goes over these extensions as well as JDO/JPA things that might be particularly useful with GAE, with examples of how they're useful with GAE. For example, parent-pk, and then in Max's recent article, @PrePersist, @PreUpdate, and the JDO StoreCallback interface, which I didn't know about.
Ikai L (Google) wrote: > I'm happy to add this to the official docs if it isn't clear. I think > this makes sense under the JPA section or the section about ancestor > queries. > > On Sun, Nov 22, 2009 at 11:24 PM, Rusty Wright <[email protected] > <mailto:[email protected]>> wrote: > > There are way too many hidden secrets, like this parent-pk query, > that are buried throughout the App Engine documentation. It would > really be nice if these things were more clearly documented. > > > Ikai L (Google) wrote: > > Hey Todd, > > > > There are a few different things you can do here: > > > > 1. Use the parent-pk filter. It looks something like this: > > > > query = pm.newQuery("select from Account " + > > > > "where parent-pk == keyParam " + > > "parameters Key keyParam"); > > > > > > There's a groups thread about this here: > > > > http://groups.google.com/group/google-appengine-java/browse_thread/thread/97ba3209ec6a65de > > > > and the docs are here: > > > > > > http://code.google.com/appengine/docs/java/datastore/transactions.html#Using_Transactions(search > > > > 2. Use the low-level API. > > > > com.google.appengine.api.datastore.Query has a constructor that > takes an > > Ancestor key. > > > > http://code.google.com/appengine/docs/java/javadoc/com/google/appengine/api/datastore/Query.html#Query(com.google.appengine.api.datastore.Key) > > > > Hope this helps. > > > > On Mon, Nov 16, 2009 at 4:29 PM, Todd Vierling <[email protected] > <mailto:[email protected]> > > <mailto:[email protected] <mailto:[email protected]>>> wrote: > > > > Test app to reproduce: > > > > http://ancestortest.latest.duh-test.appspot.com/ > > > > Source code: > > > > > > http://ancestortest.latest.duh-test.appspot.com/src/ancestortest/AncestorTestServlet.java > > > > http://ancestortest.latest.duh-test.appspot.com/src/ancestortest/UserAccount.java > > > > http://ancestortest.latest.duh-test.appspot.com/src/ancestortest/UserAccountModification.java > > > > This sample code basically creates two UserAccount objects and > > attaches a UserAccountModification to one of them. Then, a query > > (which, unless the datastore is really slow, should return an > empty > > list): > > > > ===== > > Query q = em.createQuery("select m from > > UserAccountModification m where m.modTime < :newest and m.owner > > = :owner order by modTime desc"); > > q.setParameter("newest", System.currentTimeMillis() - > > 10000L); > > q.setParameter("owner", user1); > > List<UserAccountModification> mods = > q.getResultList(); > > ===== > > > > I get the following exception: > > > > javax.persistence.PersistenceException: SELECT FROM > > UserAccountModification m WHERE m.modTime < :newest and m.owner > > = :owner ORDER BY modTime desc: Key of parameter value does > not have a > > parent. > > at > > > org.datanucleus.jpa.NucleusJPAHelper.getJPAExceptionForNucleusException > > (NucleusJPAHelper.java:264) > > at > org.datanucleus.jpa.JPAQuery.getResultList(JPAQuery.java:179) > > at > > ancestortest.AncestorTestServlet.doGet(AncestorTestServlet.java: > > 46) > > > > I must be missing something here. The docs for GAE talk about > > ensuring the use of ancestor filters when inside a > transaction, for > > instance, and there's the ANCESTOR IS operator in GQL. > However, I > > can't seem to figure out how properly to express this in JPQL (as > > "ANCESTOR IS" is a syntax error there), and there's no docs > that I can > > find on doing this in JPA. > > > > The query is meant to find UserAccountModification objects all > > residing under a given "owner", which happens to be the > ancestor of > > those objects. Is there a proper expression for this using JPQL? > > > > -- > > > > 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 > > [email protected] > <mailto:[email protected]> > > <mailto:[email protected] > <mailto:[email protected]>>. > > To unsubscribe from this group, send email to > > [email protected] > <mailto:google-appengine-java%[email protected]> > > <mailto:google-appengine-java%[email protected] > <mailto:google-appengine-java%[email protected]>>. > > For more options, visit this group at > > http://groups.google.com/group/google-appengine-java?hl=. > > > > > > > > > > > > -- > > Ikai Lan > > Developer Programs Engineer, Google App Engine > > > > -- > > > > 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 > [email protected] > <mailto:[email protected]>. > > To unsubscribe from this group, send email to > > [email protected] > <mailto:google-appengine-java%[email protected]>. > > For more options, visit this group at > > http://groups.google.com/group/google-appengine-java?hl=. > > -- > > 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 > [email protected] > <mailto:[email protected]>. > To unsubscribe from this group, send email to > [email protected] > <mailto:google-appengine-java%[email protected]>. > For more options, visit this group at > http://groups.google.com/group/google-appengine-java?hl=. > > > > > > -- > Ikai Lan > Developer Programs Engineer, Google App Engine > > -- > > 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 [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/google-appengine-java?hl=. -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. 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