Nick, The Puts in the code snippet really mustn't 'always put the entity'. It is crucial in this scenario that one of the Puts fails. If all Puts always succeed (barring non-concurrent failures) then the transactions definitely don't work.
With respect I can't not "*worry about how they work, you just need to trust they do". *My expectation is that the App Engine datastore really is like every other persistence software I've ever used. If you look closely at the isolation guarantees given by popular relational databases you will see a raft of complex and surprising edge cases. A good review of these complexities to be found is http://www.xaprb.com/blog/2014/12/08/eventual-consistency-simpler-than-mvcc/ Francis On 17 May 2015 at 22:42, Nick <[email protected]> wrote: > Apologies, forgot one important item: > > 6. The datastore uses a restful interface. A put always puts the entity, > regardless of whether it already exists or not. If you use a deterministic > key the behavior you seek will just happen. It will create an entity if > none exists, or update the existing one if it does. > > -- > You received this message because you are subscribed to a topic in the > Google Groups "Google App Engine" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/google-appengine/NagJ97YExB0/unsubscribe > . > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/google-appengine. > To view this discussion on the web visit > https://groups.google.com/d/msgid/google-appengine/bff8ff78-e87d-4c47-ade9-9f83249c5777%40googlegroups.com > . > For more options, visit https://groups.google.com/d/optout. > -- Francis Stephens Software Developer @ Belua -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/CAG1f2XCreTw_FN6Wx%3Dm_d%3DQdFVSs3wkrh8w4BrkqsmOaM7s8kg%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
