how to implement JPA I have developed an application in Java that is registered on Google App Engine. I need to store some data on data store. But, I am completely unaware about its implementation. 

Actually, I have implemented OAuth, so I want to store data of particular user who has logged in. Is it possible to separate out data stores for different users ?

Also, there is some quota limitation. How much data can we store for whole application ?
a quick search in google gave me this:


Using JPA with App Engine
Quotas


Also, in the datastore you can store only entities, this means that when you save some user data, it will be stored in the Users entity with all the other users data, what you have to do is implement relationships between entities like in a regular database (MySQL, SQL Server, etc.), check it out here:


Using the Datastore with JDO