You are better off using a copy constructor and controlling exactly what attributes need to be cloned.
So, if you have a Post
entity like this one:
@Entity(name = "Post")
@Table(name = "post")
public class Post {
@Id
@GeneratedValue
private Long id;
private String title;
@OneToMany(
mappedBy = "post",
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<PostComment> comments = new ArrayList<>();
@OneToOne(
mappedBy = "post",
cascade = CascadeType.ALL,
orphanRemoval = true,
fetch = FetchType.LAZY
)
private PostDetails details;
@ManyToMany
@JoinTable(
name = "post_tag",
joinColumns = @JoinColumn(
name = "post_id"
),
inverseJoinColumns = @JoinColumn(
name = "tag_id"
)
)
private Set<Tag> tags = new HashSet<>();
//Getters and setters omitted for brevity
public void addComment(
PostComment comment) {
comments.add(comment);
comment.setPost(this);
}
public void addDetails(
PostDetails details) {
this.details = details;
details.setPost(this);
}
public void removeDetails() {
this.details.setPost(null);
this.details = null;
}
}
It does not make sense to clone the comments
when duplicating a Post
and using it as a template for a new one:
Post post = entityManager.createQuery("""
select p
from Post p
join fetch p.details
join fetch p.tags
where p.title = :title
""", Post.class)
.setParameter(
"title",
"High-Performance Java Persistence, 1st edition"
)
.getSingleResult();
Post postClone = new Post(post);
postClone.setTitle(
postClone.getTitle().replace("1st", "2nd")
);
entityManager.persist(postClone);
What you need to add to the Post
entity is a copy constructor
:
/**
* Needed by Hibernate when hydrating the entity
* from the JDBC ResultSet
*/
private Post() {}
public Post(Post post) {
this.title = post.title;
addDetails(
new PostDetails(post.details)
);
tags.addAll(post.getTags());
}
This is the best way to address the entity clone/duplication problem. Any other methods, which try to make this process completely automatic, miss the point that not all attributes are worth duplicating.