again about JPA/Hibernate bulk(batch) insert

Question

Here is simple example I've created after reading several topics about jpa bulk inserts, I have 2 persistent objects User, and Site. One user could have many site, so we have one to many relations here. Suppose I want to create user and create/link several sites to user account. Here is how code looks like, considering my willing to use bulk insert for Site objects.

User user = new User("John Doe");

user.getSites().add(new Site("google.com", user));
user.getSites().add(new Site("yahoo.com", user));

EntityTransaction tx = entityManager.getTransaction();
tx.begin();
entityManager.persist(user);
tx.commit();

But when I run this code (I'm using hibernate as jpa implementation provider) I see following sql output:

Hibernate: insert into User (id, name) values (null, ?)
Hibernate: call identity()
Hibernate: insert into Site (id, url, user_id) values (null, ?, ?)
Hibernate: call identity()
Hibernate: insert into Site (id, url, user_id) values (null, ?, ?)
Hibernate: call identity()

So, I means "real" bulk insert not works or I am confused?

Here is source code for this example project, this is maven project so you have only download and run mvn install to check output.

UPDATED:

After Ken Liu kindly advise, I've disabled Site object id auto generation:

User user = new User("John Doe");

user.getSites().add(new Site(1, "google.com", user));
user.getSites().add(new Site(2, "yahoo.com", user));
entityManager.setFlushMode(FlushModeType.COMMIT);
EntityTransaction tx = entityManager.getTransaction();
tx.begin();
entityManager.persist(user);
tx.commit();

Now I have following line in debug output:

DEBUG: org.hibernate.jdbc.AbstractBatcher - Executing batch size: 2

It works!

Answer 1

If you're using the database to generate ids, then Hibernate has to execute a query to generate the primary key for each entity.