Question

这类似于How to cascade persist using JPA/EclipseLink

我必须这样的实体。一个是RoomEntity，它与ComputerEntity有一对多的双向关系。例如。每个房间都有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

当我尝试用这样的电脑坚持新房间时：

    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是一个无状态EJB，roomBean.createRoom只调用entityManager.persist（room）。由于我在RoomEntity的计算机字段上有一个CascadeType.PERSIST，因此创建了ComptuerEntity。但是，如果我查看该ComputerEntity的房间字段，我会看到该房间字段为空。因为我有双向关系，所以我认为Eclipselink会自动填充房间。为了以这种方式设置房间，我不得不添加

        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？

感谢。 -Noah

Answer 1

JPA没有关系维护。 EJB 2.1表明，通用关系管理效率低下且过于繁琐。

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

EclipseLink / JPA2 ManyToOne双向级联持续存在问题

1 个答案: