Google Appengine NDB 祖先 vs 键查询 [英] Google Appengine NDB ancestor vs key query

问题描述

我将一个实体的键存储为另一个实体的属性，以便将它们关联起来.在项目的这一点上，我们处于重构阶段，所以我在考虑引入祖先.这两种方法之间是否存在性能差异?如果我们介绍祖先，我可能会获得什么优势?

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)

第一个祖先查询方法

qry = Article.query(ancestor=book_key)

第二个简单的键查询方法

qry = Article.query(book_key=book_key)

推荐答案

祖先查询将始终完全一致.另一方面，通过 book_key 查询不一定一致:您可能会发现该查询中不会显示最近的更改.

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.

另一方面，引入祖先对更新次数施加了限制:您每秒只能对任何实体组(即祖先及其子代)进行一次更新.

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).

对于您的应用中哪一个更重要，这对您来说是一种权衡.

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

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