休眠保存/更新级联

Question

There is a class A like:

class A {
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     @Basic(optional = false)
     @Column(name = "DBId")
     private Long DBId = null;

     @OneToMany(cascade = CascadeType.ALL)
     @LazyCollection(LazyCollectionOption.FALSE)
     List<B> list;
}

and a class B like

class B {
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     @Basic(optional = false)
     @Column(name = "DBId")
     private Long DBId = null;
}

When I want to persist a new instance of class A, two cases are possible. 1- All instances of B in A are new, in which case, a simple session.save(A) is ok. 2- Some or all of the instances of B in A are old. How should I save A in order not to have duplicate Bs. Will saveOrUpdate solve the problem? or it will just decide to choose save or update just by looking at A, and for example if A was new, it will also call save on Bs, and if A was old, it will also call update on Bs?

Furthermore, I saw that I had just a simple session.save(A) in my codes, and it did not produce redundant Bs. Am I wrong? Is this possible?

Regards

UPDATE: in case of old Bs, the instances of old Bs are attached to the session, and DBId is correctly set.

Answer 1

Do your entities live longer than sessions? If not, you don't have to use update() or saveOrUpdate() . When you call session.save() , Hibernate knows whether to insert or update , by checking the state of the entity. You can read here for more about states: http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html_single/#objectstate-overview

The same applies to the cascade. When the operation is cascaded to the collection, Hibernate will check the state of the entities in the collection and will NOT try to insert them, if they are already in PERSISTENT state.