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

magicmory :

@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!

Trần Quốc Vũ :

You should use jpa method:

List<Comment> findByChildrenCommentsIsNull();

to get all the root comments and their nested replies.