I have 3 table A ,B and mapping table A_B, which contains Id's of both (A_ID and B_ID). Following is how the java classes which map these 3 tables look like:
@Entity
@Table(name = "A")
public class A {
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE)
@Column(name = "ID")
private Long id;
@OneToMany(cascade=CascadeType.ALL)
@JoinColumn(name = "FK_A", referencedColumnName="Id", nullable = false)
private Set<A_B> ab;
//Other attributes, Getters Setters etc.
}
@Entity
@Table(name = "A_B")
public class A_B {
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE)
@Column(name = "ID")
private Long id;
@ManyToOne(cascade=CascadeType.ALL)
@JoinColumn(name = "FK_B", nullable = false)
private B b;
//Other attributes, Getters Setters etc.
}
Entity
@Table(name = "B")
public class B {
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE)
@Column(name = "ID")
private Long id;
//Other attributes, Getters Setters etc.
}
Now lets say I have already persisted an object of B (b). Now I want to persist an Object of A (a) and the association between these two (ab). I have my code like :
@PersistenceContext(unitName = "demoPU")
private EntityManager em;
B b = em.createNamedQuery(queryName, B); // Getting obj of B
A a = new A();
A_B ab = new A_B();
ab.setB(b); // Setting B in relationship
a.setAb(ab);
em.persist(a);
However this tried to persist b again & since its id is already set, it throws en exception:
org.hibernate.PersistentObjectException: detached entity passed to persist
Can you let me know how can I persist the association in this case without having to persist B again ?
