Spring boot JPA Hibernate return nested Json Object : Reddit style comment system

Question

@Entity
public class Comment {
 @Id @GeneratedValue(strategy = GenerationType.IDENTITY) 
 private Long id;
 private String content;
 @ManyToOne(fetch = FetchType.EAGER)
 @JoinColumn(name = "parent_id")
 private Comment parentComment;
 @OneToMany(mappedBy="parentComment", cascade = CascadeType.ALL)
 private List<Comment> childrenComments = new ArrayList<>(); 
}
public interface CommentRepository extends JpaRepository<Comment, Long> {
}

Here is how I am saving replies for a specific comment.

Comment parent = new Comment();
 parent.setContent(" 1 comment");
 parent = commentRepository.save(parent);
 Comment reply1 = new Comment();
 reply1.setContent("reply 1 to comment 1");
 reply1.setParentComment(parent);
 Comment reply2 = new Comment();
 reply1.setContent("reply 2 to comment 1");
 reply1.setParentComment(parent);
 parent = commentRepository.save(parent);

When I do commentrepository.findAll()

I would like to return the following json data.

{
 "id": 1,
 "content": "1 comment",
 "replies" :[
 {
 "id": 2,
 "content": "reply 1 to comment 1"
 },
 {
 "id": 3,
 "content": "reply 2 to comment 1"
 }
 ]
 }

My goal is to build a reddit style comment system. Where each comment has an array of comments(replies). When I query for all comments, using spring data jpa, I only want the root comments and their nested replies.

In the above case, don't want something like this:

{
 {
 "id": 1,
 "content": "1 comment",
 "replies" :[
 {
 "id": 2,
 "content": "reply 1 to comment 1"
 },
 {
 "id": 3,
 "content": "reply 2 to comment 1"
 }
 ]
 }
 {
 "id": 2,
 "content": "reply 1 to comment 1"
 }
 {
 "id": 2,
 "content": "reply 1 to comment 1"
 }
}

I have spent several days on this without success. I have tried using @jsonIgnore and other jackson annotations without success. Any suggestions or recommendations? Thank you in adavance. you are appreciated!

Answer 1

You should use jpa method:

List<Comment> findByChildrenCommentsIsNull();

to get all the root comments and their nested replies.

• magicmory: thanks for the hint. What I actually wanted is commentRepository.findByParentCommentIsNull()

Answer 2

the answer is:

List<Comment> comments = commentRepository.findByParentCommentIsNull();

• Sangam Belose: Dont just include the code. Kindly explain how your answer will solve the issue.Try to follow stackoverflow.com/help/how-to-answer