如何持久保存列表类型的属性 <Object> 在JPA中？

Question

What is the best way to get a List with Objects persisted? I'm using JavaEE 7 with JPA. Object B is also an Entity.

My Model

@Entity
public class ObjectA implements Serializable {

    @Id @GeneratedValue
    private Long id;

    // What should I use here?
    private List<ObjectB> objectList;

    public ObjectA () {
        this.objectList = new ArrayList<ObjectB>();
    }
}

My JPA Calls

@Stateless
@JPA
public class ObjectJPA{

    @PersistenceContext(unitName = "ObjectProjectPU")
    private EntityManager em;

    // How can I insert a record in the table for objectList here?
    public void insertIntoObjectList(ObjectB objectB) {
        em.persist(objectB); // This must be wrong?
    }
}

What I prefer is that my database table for objectList would look like this:

id (ObjectA_id) | objectB_id     or    id | ObjectA_id | objectB_id

Answer 1

Your ObjectA class should look like below.

 @Entity public class ObjectA implements Serializable { @Id @GeneratedValue private Long id; // What should I use here? private List<ObjectB> objectList; @OneToMany(mappedBy = "objectB_id") public List<ObjectB> getObjectList() { return objectList; } public void setObjectList(List<ObjectB> listOfObjetB) { this.objectList = listOfObjetB; } public ObjectA () { this.objectList = new ArrayList<ObjectB>(); } } 

This will create a relation between your class A and B.

Follow the example given to the below link properly. It will help you to understand the JPA one to many relationship. :)

Answer 2

I figured out that it was pretty easy.

ObjectA Model

@OneToMany
@JoinTable
(
    name="OBJECTA_OBJECTB",
    joinColumns={ @JoinColumn(name="ID", referencedColumnName="ID") },
    inverseJoinColumns={ @JoinColumn(name="OBJECTB_ID", referencedColumnName="ID") }
)
private List<ObjectB> objectList;

JPA CALL

public void insertIntoObjectList(ObjectB object) {
    object.setSomeDataInObjectList(list); // just a random list here
    em.persist(object); 
}

ObjectB Model

@ManyToOne
ObjectA objectA;