We have an application that runs on a traditional J2EE environment and Google App Engine, with as identical code base as possible. We use JDO for persistance. In Google App Engine you need to use Key objects as the primary key for owned relations in an entity group. Obviously we can’t use the Key class as our primary key if we want to be portable, since it’s not available in a non Google App Engine class path.
Google App Engine supports encoded strings as keys, however this breaks automatic identity value generation in most RDBMS. To work around this you would have to handle Continue reading Creating portable owned JDO relations on Google App Engine