Answers below. -- Ikai Lan Developer Programs Engineer, Google App Engine plus.ikailan.com
On Tue, Jan 17, 2012 at 9:24 AM, Paul Bartosik <paulhbarto...@gmail.com>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 > google-appengine-java@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-java@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.
