Transactions

Transactions on the Cloud Datastore behave differently to those of a SQL database. It's worth reading the Cloud Datastore transactions documentation to familiarise yourself with their behaviour. Crucially:

"queries and lookups inside a Datastore mode transaction do not see the results of previous writes inside that transaction".

This is partially mitigated by our caching system. For more info on how querying and caching work see the caching docs.