On the google app engine, why do updates not reflect in a transaction?
Looks like you are not doing a commit on the  transaction before querying

start a db transaction
update entityX by setting entityX.flag = True
save entityX
COMMIT TRANSACTION
query for entity where flag == True. BUT, here is the problem. This query does NOT return any results. It should have returned entityX, but it did not.

In a transaction, entities will not be persisted until the transaction is commited
I store groups of entities in the google app engine Data Store with the same ancestor/parent/entityGroup. This is so that the entities can be updated in one atomic datastore transaction.
The problem is as follows:

I start a db transaction
I update entityX by setting entityX.flag = True
I save entityX
I query for entity where flag == True. BUT, here is the problem. This query does NOT return any results. It should have returned entityX, but it did not.

When I remove the transaction, my code works perfectly, so it must be the transaction that is causing this strange behavior.
Should updates to entities in the entity group not be visible elsewhere in the same transaction?
PS: I am using Python. And GAE tells me I can't use nested transactions :(