On Monday, 1 August 2011 11:16:40 UTC+1, Stephen wrote: > > Even though you're allocating from two ranges rather than one, that's > still less than the datastore would do things automatically, so you > still have to be careful. > > For example, suppose you later add an admin web interface that can > also create new cars and add them to garages. If you let the datastore > allocate IDs, the first car you add to any garage through this new > code path will get ID 1 or thereabouts, because children get an ID > from the range associated with their parent. Eventually the > admin-generated car IDs may clash with those pre-allocated from the > global car sequence given out to remote clients, and old data will be > over written. > > So you might want to enforce that a Car model can't be created without > passing in an ID. > I think I'm only now getting the subtlety of my faulty assumption.
db.allocate_ids for a given kind does not give unique IDs for that kind, it gives IDs that are only unique for that kind AND for a specific parent as specified by the key used to make the call to db.allocate_ids(). So I can't pre-allocate a bunch of IDs that can be used to make keys with whatever parent may be required without running the risk of duplicate IDs because the ID allocation mechanism, like the Keys themselves, is actually parent specific. This pretty much blows pre-allocated IDs out of the water for me, at least for what I had in mind, unless I either drop entity groups altogether, or do something like like put all items into an an entity group per user (so the parent is something that represents the user, meaning that I know the parent to use). Of course I could just manage my own ID allocation, but I'm never really keen on that when a data persistance layer has its own ID/Key mechanism. Oh well, back to the drawing board, thanks for the patient explanations -- Tim -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/fZyPanewo-AJ. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
