I don't think you can do that for the price of a small operation.
An alternative would be to insert the ID of an entity into memcache
whenever it's accessed for other reasons, then check memcache first
whenever you want to do the existence check.
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-Vinny P
Technology Media
i thought there was a way to see if a database key exists for the price of
one small operation?
doing keyobj = Key.from_path, followed by filter( '__key__ =', keyobj ),
followed by query.get() using key only query, you are charged one large and
one small operation and only get the key
