CODEWITHSUNDEEP
javagoogle-cloud-datastoreobjectify
morpheus05
morpheus05

Reputation: 4872

Most efficient way to read many to many objects from GAE datastore

I've read some questions and articles about many to many relations in the google datastore but I'm still not sure which is the most efficient way in my case: I have a User which references N CollectionOfThings. A CollectionOfThings can reference M users. Both, M and N are very small. I except no more then 5. (Nature of my application). The user object is fetched almost in every request. The other object not. I need to query from an instance of CollectionOfThings all users and from a user all instances of her CollectionOfThing instances.

So I see to possible implementations:

Now the big question is: What is the most efficient way in perspective of data store read operations?

Upvotes: 0

Views: 54

Answers (1)

stickfigure
stickfigure

Reputation: 13556

Start with the simplest/easiest approach, you can always migrate later. From what you describe, I would start with Set<Ref> fields pointing in both directions. You can use @Load groups so that the loads don't happen by default but you still have the facility available. Make sure to update both ends of the relationship in a transaction.

Another option, assuming the User<->CollectionOfThings relationship is symmetric bidirectional, is to only keep the Set of keys/refs on one side and @Index it. This has the advantage that you don't need a transaction to keep the bidir relationship in sync. It has the disadvantages that you use queries to follow the relationship in the inverse direction; those queries will be eventually consistent; it costs extra to maintain those indexes.

Upvotes: 1

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