Google Appengine NDB ancestor vs key query

Question

I am storing a key of an entity as a property of another in order to relate them. We are in a refactor stage at this point in the project so I was thinking about introducing

Answer 1

The ancestor query will always be fully consistent. Querying by book_key, on the other hand, will not necessarily be consistent: you may find that recent changes will not be shown in that query.

On the other hand, introducing an ancestor imposes a limit on the number of updates: you can only do one update per second to any entity group (ie the ancestor and its children).

It's a trade-off for you as to which one is more important in your app.