On second examination, I could be wrong about JPA. I'll need to test this and see.
http://stackoverflow.com/questions/4909012/how-to-create-an-object-in-a-specific-entity-group-with-jpa-google-appengine-j If you get around to this before me, can you let me know if it works? Note that as of a recent release, you can do cross entity-group transactions. -- Ikai Lan Developer Programs Engineer, Google App Engine plus.ikailan.com On Wed, Jan 18, 2012 at 11:22 AM, Ikai Lan (Google) <[email protected]>wrote: > Answers below. > > -- > Ikai Lan > Developer Programs Engineer, Google App Engine > plus.ikailan.com > > > > On Tue, Jan 17, 2012 at 9:24 AM, Paul Bartosik <[email protected]>wrote: > >> I have spent a bit of time banging up against Entity Group issues. In >> all cases, the problem was with my JPA. I had made mistakes in my >> annotations that manifested as run-time transaction and Entity Group >> errors . >> >> The documentation on JPA relationships and Entity Groups is pretty >> light. Can someone confirm my 3 assumptions below? >> >> 1. In a bi-directional relationship, the unowned side of the >> relationship will automatically be the Parent Entity and the owned >> side will be the Child Entity. >> > > No, there's nothing automatic about parent and child entity relationships > with regards to JPA. In JPA parlance, "parent" and "child" refer to a > one-many relationship, whereas in an entity group, the "ancestry" of an > entity is embedded entirely within its key. > > >> >> 2. In a uni-directional relationship, both sides of the relationship >> will be in different Entity Groups. >> >> Again, there's nothing automatic about this. > > >> 3. When using JPA, there is no other way to specify the Entity Group >> of your entities. >> > > You can specify the entity groups of an entity by constructing the key via > a KeyFactory: > > > http://code.google.com/appengine/docs/java/javadoc/com/google/appengine/api/datastore/KeyFactory.Builder.html > > A lot of this confusion may come from the fact that the entity group > concept does not map well to JDO/JPA. In a relational database, a single > entity can have 1:N mappings to many different kinds of "child" entities (a > School can have many Students, Teachers and Specialities, for instance), > whereas an entity group is a single, hierarchical structuring of data (a > User has many Blogs which have Entries which each have Comments). > > Do you have any experience with the low-level API? You'll develop some > familiarity with datastore concepts if you take a look at it for a bit. > > >> >> >> Thanks for any help. >> >> -Paul >> >> -- >> 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=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 [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=en.
