Oops. Link is here: http://gae-java-persistence.blogspot.com/2009/10/optimistic-locking-with-version.html
On Thu, Apr 8, 2010 at 10:00 AM, Ikai L (Google) <ika...@google.com> wrote: > Here's a blog post Max Ross wrote about optimistic locking using built in > features of JDO/JPA > > > On Thu, Apr 8, 2010 at 2:42 AM, mscwd01 <mscw...@gmail.com> wrote: > >> Thanks John. So basically the process should be: >> >> - Query for the object inside a transaction >> - Update the object counter >> - Commit >> >> - If commit fails - re-query the datastore for the same object? >> >> Is it possible to just catch the exception and try committing the >> object again or will I have to query the datastore for the object >> again? >> >> Also will it work when you query for a parent object and then update >> the counter of a child object? >> >> Thanks again. >> >> On Apr 8, 10:33 am, John Patterson <jdpatter...@gmail.com> wrote: >> > You will need to read and update the object in a transaction which >> > will throw an exception on commit if another thread updates the same >> > entity. You can then refresh the object and try again. Also look >> > into memcache which has an atomic counter increment method that is >> > much faster than reading and writing to the datastore. The downside >> > is that the counts could be reset so you may need to periodically >> > store them in the datastore. >> > >> > On 8 Apr 2010, at 16:17, mscwd01 wrote: >> > >> > >> > >> > > Hey, >> > >> > > How do you ensure, once you have queried an object from the datastore, >> > > that another call to that object cannot be made? >> > > I basically have a bunch of objects with counters which get >> > > incremented during each call to that object. >> > >> > > What I need to ensure is the object doesn't get called by two threads, >> > > each of which increment the counter by 1 and persist the object back >> > > to the datastore, only for the counter to be incremented by 1 and not >> > > by 2. >> > >> > > Thanks >> > >> > > -- >> > > 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<google-appengine-java%2bunsubscr...@googlegroups.com> >> > > . >> > > For more options, visit this group athttp:// >> 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-j...@googlegroups.com. >> To unsubscribe from this group, send email to >> google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com> >> . >> For more options, visit this group at >> http://groups.google.com/group/google-appengine-java?hl=en. >> >> > > > -- > Ikai Lan > Developer Programs Engineer, Google App Engine > http://googleappengine.blogspot.com | http://twitter.com/app_engine > -- Ikai Lan Developer Programs Engineer, Google App Engine http://googleappengine.blogspot.com | http://twitter.com/app_engine -- 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.
