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 ancestors. Is there a performance difference between the two approaches? Any given advantages that I might gain if we introduce ancestors?
class Book(ndb.Model):
...
class Article(ndb.Model):
book_key = ndb.KeyProperty(kind=Book, required=True)
book_key = ndb.Key("Book", 12345)
1st ancestor query approach
qry = Article.query(ancestor=book_key)
2st simple key query approach
qry = Article.query(book_key=book_key)
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.