问题
My app should contain several users, each of them having a list of objects ( only one user own the object ). My question is : Would it be better to put an entity User that references the Ids of its objects, or should I put the user as the ancestor of the objects ? Please be kind, I am just beginning with nosql and datastore !
回答1:
What approach you take will depend heavily on your access patterns, what make sense for easy retrieval, frequency of writes etc. You start your design process by building a basic entity relationship model, then start elaborating on what information you need to get to, and how frequently it is required what security restrictions are required. Then look at how you need to adjust the real model to reflect these access use cases taking into account performance, ease of use, security requirements.
回答2:
Which approach you should choose depends mainly on the consistency model (strong vs eventual) you require for your entities. In Google Cloud Datastore, an entity group (an entity and its descendants) is a unit with strong consistency, transactionality, and locality.
You can read more on the topic here and here.
And there is one more important thing that is needed to take into account. If you model a parent-child relationship between a user and an object, the parent will be part of the object's key hence if you will change the object's owner later, you will end up with different object in terms of its key.
来源：https://stackoverflow.com/questions/21035003/should-i-put-the-user-in-the-ancestor-path-or-separately