JPA/Hibernate bulk(batch) insert

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!