Hi Jeff and Max: Sorry to jump in this debate on the use of system generated Long id and user-provided long id and String name. I found the discussion is useful from best practice.
I leverage Objectify and try to re-do our data model. Originally, i chose the route of String name for user, role and group to enforce the unique name of the entity Key, plus long id provided from a simple ConcurrentHashMap Singleton. But i feel that the home-grown ConcurrentHashMap Singleton may not be as robust and scalable as the generated Long id, recognizing that the generated id is not contiguous. So i decided the use of String name of natural uniqueness such as email for user lock-in and generated Long id is for others. Please comment and/or siggestion. Duong BaTien DBGROUPS and BudhNet On Mon, 2010-02-22 at 13:52 -0800, Jeff Schnitzer wrote: > On Mon, Feb 22, 2010 at 1:19 PM, Max Ross (Google) > <maxr+appeng...@google.com> wrote: > > > > user-defined long-id keys are not quite as easily used. You either need to > > commit to not letting the datastore generate ids for that kind or you need > > to reserve a batch of ids using the DatastoreService.allocateIds method. > > Otherwise you run the risk of a silent collision. There is no such risk > > with user-defined string keys. > > Right, but if the user has a natural key (long, String, whatever) they > won't be using the generator anyways. There are plenty of natural > long keys in the world... facebook userid being a popular one. > > FWIW, Objectify makes the distinction between ids of type Long, which > can be null and thus autogenerated, and long (the primitive) which > cannot be autogenerated. I really hadn't intended to plug Objectify > here, really! > > > Valid point about renaming, but going back to the example I provided, the > > datastore does not distinguish between inserts and updates. The only way > > you can guarantee that an entity was inserted, and therefore the only way > > you can guarantee the uniqueness of the name, is to use a user-defined key. > > If you're mapping id to name it will be possible to create two entities with > > the same name. It's of course up to you to decide how important this is to > > defend against, but without the ability to provide your own id you wouldn't > > get to make this choice, and without the ability to provide your own string > > id you wouldn't be able to add some application-specific meaning to this > > choice. > > I totally agree with you WRT user-defined vs generated values, I just > don't see anything wrong with using the long id as a user-defined > value. Just make sure you never ask for a generated one. Seems > pretty straightforward. > > Jeff > -- 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.
