Google Appengine NDB ancestor vs key query

问题

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)

回答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.

来源：https://stackoverflow.com/questions/17191471/google-appengine-ndb-ancestor-vs-key-query