如何使用Hibernate[复制]创建实体的副本

Question

我有一个实体用户：

@Entity
@Table(name = "users")
public class User{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @Column(name = "name", nullable = false)
      private String name;

     @OneToMany(fetch = FetchType.LAZY, mappedBy = "parentid", cascade=CascadeType.ALL)
    private List<Lesson> lessonList=new ArrayList<>();
}

和实体课程

    @Entity
    @Table(name = "lesson")
    public class Lesson{

        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private int id;

        @Column(name = "name", nullable = false)
          private String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parentid")
    private User parentid;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "parentid2", cascade=CascadeType.ALL)
        private List<Exercise> exerciseList=new ArrayList<>();
    }

我需要制作 user1 课程的副本（深度副本），并将此副本添加到另一个用户 2。最后，我需要用户1有课程，用户2有课程的副本。

Answer 1

最简单的方法是使用XStream api。用＜code＞@xstreamitfield＜/code＞注释@Id字段，然后将对象写入xml，如下所示。

XStream xstream = new XStream(new StaxDriver());
String xml = xstream.toXML(yourObject);

把它读回来

YourObject yourObject = (Person)xstream.fromXML(xml);