[SOLVED] How to create entities in one Entity group?

How to create entities in one Entity group?

I am building an app based on google app engine (Java) using JDO for persistence.

Can someone give me an example or a point me to some code which shows persisting of multiple entities (of same type) using javax.jdo.PersistenceManager.makePersistentAll() within a transaction.

Basically I need to understand how to put multiple entites in one Entity Group so that they can be saved using makePersistentAll() inside transaction.

Solution

Thanks for the response Nick.

This document only tells about implicit handling of entity groups by app engine when its a parent-child relationship. I want to save multiple objects of same type using PeristentManager.makePersistentAll(list) within a transaction. If objects are not same Entity Group this throws exception. Currently I could do it as below but think there must be a better and more appropriate approach to do this -

User u1 = new User("a");
UserDAO.getInstance().addObject(user1); 
// UserDAO.addObject uses PersistentManager.makePersistent() in transaction and user 
// object now has its Key set. I want to avoid this step.

User u2 = new User("x"); 
u2.setKey(KeyFactory.createKey(u1.getKey(),User.class.getSimpleName(), 100 /*some random id*/)); 

User u3 = new User("p");
u3.setKey(KeyFactory.createKey(u1.getKey(), User.class.getSimpleName(), 200)); 

UserDAO.getInstance().addObjects(Arrays.asList(new User[]{u2, u3})); 
// UserDAO.addObjects uses PersistentManager.makePersistentAll() in transaction.

Although this approach works, the problem with this is that you have to depend on an already persistent entity to create an entity group.