EclipseLink/JPA2 ManyToOne 双向级联持续存在问题

Question

这类似于 如何使用 JPA/EclipseLink 级联持久化

我有像这样的实体。一种是 RoomEntity，它与 ComputerEntity 具有一对多的双向关系。例如。每个房间有 0..n 台电脑。

@Entity
public class ComputerEntity implements Serializable {
    @Id
    @GeneratedValue(generator="computerSeq",strategy= GenerationType.SEQUENCE)
  @SequenceGenerator(name="computerSeq",sequenceName="SEQUENCECOMPUTERID",allocationSize=1)
    private long computerID;

    @Column(name = "COMPUTERID")
    public long getComputerID() {
        return computerID;
    }

    public void setComputerID(long computerID) {
        this.computerID = computerID;
    }

    private RoomEntity room;

    @ManyToOne()
    @JoinColumn(name = "ROOMID", referencedColumnName = "ROOMID")
    public RoomEntity getRoom() {
        return room;
    }

    public void setRoom(RoomEntity room) {
        this.room = room;
    }

} //ComputerEntity

@Entity
public class RoomEntity {

    @Id
    @GeneratedValue(generator="roomSeq",strategy= GenerationType.SEQUENCE)
    @SequenceGenerator(name="roomSeq",sequenceName="SEQUENCEROOMID",allocationSize=1)
    private long roomID;

    @OneToMany(mappedBy = "room", cascade = {CascadeType.PERSIST, CascadeType.REMOVE})
    private Set<ComputerEntity> computers;

    @javax.persistence.Column(name = "ROOMID")
    public long getRoomID() {
        return roomID;
    }

    public void setRoomID(long roomID) {
        this.roomID = roomID;
    }

    public Set<ComputerEntity> getComputers() {
        return computers;
    }

    public void setComputers(Set<ComputerEntity> computers) {
        for(ComputerEntity computer : computers) {
            computer.setRoom(this);
        }
        this.computers = computers;
    }
}//RoomEntity

当我尝试使用计算机持久保存一个新房间时，如下所示：

    RoomEntity room = new RoomEntity();
    room.setAdministrator("Fox Moulder");
    room.setLocation("Area 51");

    ComputerEntity computer1 = new ComputerEntity();
    computer1.setDescription("Alienware area51 laptop");
    Set<ComputerEntity> computers = new HashSet<ComputerEntity>();
    computers.add(computer1);

    room.setComputers(computers);

    roomBean.createRoom(room);

roomBean 是无状态 EJB，而 roomBean.createRoom 只需调用entityManager.persist(room)。由于我在 RoomEntity 的计算机字段上有 CascadeType.PERSIST，因此创建了 ComptuerEntity。但是，如果我查看该 ComputerEntity 的 room 字段，我会发现 room 字段为空。我本以为 Eclipselink 会自动填充房间，因为我有双向关系。为了以这种方式设置房间，我必须添加

        for(ComputerEntity computer : computers) {
            computer.setRoom(this);
        }

到 room.setComputers(...)。这是正确的方法还是有办法让 Eclipselink 自动设置它？

谢谢。 -诺亚

Answer 1

JPA 中没有关系维护。 EJB 2.1 已经表明，通用关系管理效率太低而且太麻烦。

我建议添加一个 addComputer() 方法，该方法将在新添加的 ComputerEntity 上设置 RoomEntity