JPA 派生标识符的两种实现方式

方法一：@Entity@IdClass(ModuleId.class)public class Module {

@Id    private Integer index;

@Id    @ManyToOne    private Page page;

private Integer cols;}

方法二：

@Entitypublic class Element {

@EmbeddedId    private ElementId id;

@ManyToOne    @MapsId("pageId")    @JoinColumn(name = "mypage_id")    private Page page;

private String name;}