Question

I configured a simple OneToOne mapping in my entity, but when I persist the object I see a “Select” statement being executed by Hibernate just before the Insert and I don’t know why.

@Entity 
@Table( name = "USER" )
public class NewUser {

   @OneToOne
   @JoinColumn(name="user_status_type_id", nullable=false)
   private UserStatusType userStatusType;

UserStatusType is just a read-only lookup table, so nothing persists in that table when I save User.

User u = new User();
u.setUserStatusType( new UserStatusType(101));
session.persis(u);

But when I persist the User object, the output from Hibernate reads as follows:

Hibernate: select userstatus_.user_status_type_id, userstatus_.user_status_name as user2_3_ from USER_STATUS_TYPE userstatus_ where userstatus_.user_status_type_id=?
Hibernate: insert into USER (created, first_name, last_name, password, user_name, user_status_type_id) values (?, ?, ?, ?, ?, ?)

I don’t know if that’s normal for Hibernate. I figured since it was a “persist” operation I would only see an Insert statement; not sure of the purpose for the Select.

Is the mapping incorrect?

Answer 1

OK, I was able to get an answer from the Hibernate forums. To prevent the SELECT before INSERT, if you are sure the referenced row exists in the database, then use Session.load() or EntityManager.getReference().

User u = new User();
u.setUserStatusType( session.load(UserStatusType.class, new Long(id));
session.persist(u);

The session.load() method doesn’t initially load anything, it just creates a proxy for the object and avoids a hit to the database. Now, if you want to access a member (other than the id field) from the class within the context of the session, then Hibernate will go to the database. In my case I just needed the primary key from the referenced object for the INSERT, so I avoided the database hit.