祖先在谷歌应用引擎数据存储中意味着什么 [英] What does ancestor mean in the google app engine datastore
问题描述
参考: http://code.google.com/appengine/docs/python/datastore/queryclass.html#Query_ancestor
感谢。
GAE中的事务只存在于祖先后裔群组中。等同地,在我刚刚提供的URL处引用文档,
事务中的所有数据存储操作必须对实体
在同一个实体组中
和一个实体组,根据此页面在文档中定义:
当应用程序创建一个
实体时,它可以使用
来指定另一个实体
作为新实体的父项,使用
中的父参数构造函数。将父项分配给
新实体,将新实体放入与
实体相同的
实体组中。
<祖先>仅仅是父母的传递闭包 - 即给定一个实体,它的祖先是,它的父母,父母的父母等等。
Can anyone tell or define more what is "ancestor" and give an example on it and also what it is for? I just can't grasp what it really is.
Reference: http://code.google.com/appengine/docs/python/datastore/queryclass.html#Query_ancestor
Thanks.
Transactions in GAE only exist within ancestor-descendant groups. Equivalently, quoting the docs at the URL I just gave,
All datastore operations in a transaction must operate on entities in the same entity group
and an "entity group", per this page in the docs, are defined by:
When the application creates an entity, it can assign another entity as the parent of the new entity, using the parent argument in the Model constructor. Assigning a parent to a new entity puts the new entity in the same entity group as the parent entity.
"Ancestor" is just the transitive closure of "parent" -- i.e., given an entity, its ancestors are, its parent, its parent's parent, and so forth.
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