Spring JPA One To Many Infinite Recursion

im trying to return to a JPA data (converted to DTO, ofcourse) where it has a @OneToMany and @ManyToOne bidirectional relationship. Im currently apply thing fix. The problem is that the output is recusrive. comments has post has comments then has posts (comments -> post -> coments -> so on..).

I only wnat to have something like this

{
	"post_id": 1
    "user": {
        // user data
    },
    "description": "some description",
    "images": "{images,images}",
    "tags": "{tags, tags}",
	"comments": [
	 {
		//some comments data
		
	 },
	 {
		//some comments data
	 }
	]
    "lastUpdated": "2020-04-08T14:23:18.000+00:00"
}

Here are my code

This is my Posts.class

@Data
@Entity
@Table(name = "posts")
@EntityListeners(AuditingEntityListener.class)
public class Posts {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	@Column(name = "post_id")
	private Long post_id;

	@ManyToOne
	@JoinColumn(name = "user_id", nullable = false)
	private Users user;
	
	@Column(name = "description")
	private String description;
	
	@Column(name="images")
	private String images;
	
	@Column(name="tags")
	private String tags;
	
	@OneToMany(
		fetch = FetchType.LAZY,
		mappedBy = "post",
		cascade = CascadeType.ALL,
		orphanRemoval = true
	)
	@JsonIgnoreProperties(value = { "comments" ,"hibernateLazyInitializer", "handler" }, allowSetters = true)
	//@JsonManagedReference
	private List<Comments> comments;
	
		
	@LastModifiedDate
	@Column(name = "last_updated")
	private Date lastUpdated;
	
	
	public void addComments(Comments comment) {
		this.comments.add(comment);
	}
}

Here is my PostDTO.class

@Data
public class PostDTO {

	private Long post_id;
	private UserDTO user;
	private String description;
	private String images;
	private String tags;
	private List<CommentsDTO> comments;
	private Date lastUpdated;
	

}

This is my Comments.class

@Data
@Entity
@Table(name = "comments")
@EntityListeners(AuditingEntityListener.class)
public class Comments {
	
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	@Column(name="comment_id")
	private Long comment_id;
	
	@OneToOne
	@JoinColumn(name = "user_id")
	private Users user;

	@Column(name = "description")
	private String description;
	
	@Column(name="images")
	private String images;
	
	@ManyToOne
	@JoinColumn(name ="post_id" , nullable = false)
	@JsonIgnoreProperties(value = { "post" ,"hibernateLazyInitializer", "handler" }, allowSetters = true)
	//@JsonBackReference
	private Posts post;
	
	@Column(name="last_updated")
	@LastModifiedDate
	private Date lastUpdated;
	
}

Here is my CommentsDTO.class

@Data
public class CommentsDTO {
	
	private Long comment_id;
		
	private UserDTO user;
	
	private String description;
	
	private PostDTO post;
	
	private String images;
	
	private Date lastUpdated;
}

Here is my REST Controller

@GetMapping
public @ResponseBody ResponseEntity<List<PostDTO>>  getAll() throws Exception {
	
	return new ResponseEntity<List<PostDTO>>(service.getAll(), HttpStatus.OK);
}

Here is my service

public List<PostDTO> getAll() throws Exception  {
	return repo.findAll()
			   .stream()
			   .map(this::convert)
			   .collect(Collectors.toList());
}

private PostDTO convert(Posts e) {
	return  mapper.map(e, PostDTO.class);
}

Hope someone can shed light on my issue. Kinda lost as of this time.

Problem is when you convert Post into PostDTO then by using ModelMapper it calls all field's getter of Post for PostDTO. So this happened recursively for this
mapper.map(e, PostDTO.class)

So, just remove private PostDTO post from CommentDTO ,
then modelmapper don't try to set PostDTO->comment-> post field.
And you don't need bidirectional relation in DTO. DTO is all about what you want to show in response.

You are breaking the json serialization cycle on the wrong class.

You are sending a list of PostDTO, but applied JsonBackReference to Comments and JsonManagedReference to Posts

Update

Note that ObjectMapper class, JsonManagedReference and JsonBackReference may from 2 packages

• com.fasterxml.jackson.databind.ObjectMapper
• com.fasterxml.jackson.annotation.JsonManagedReference
• com.fasterxml.jackson.annotation.JsonBackReference

or:

• org.codehaus.jackson.map.ObjectMapper
• org.codehaus.jackson.annotate.JsonManagedReference
• org.codehaus.jackson.annotate.JsonBackReference

If you are not consistent between all of them, the mis-matched annotation will be ignored and you will still experience infinite loop during serialization.

Use JsonIgnoreProperties along with Manage and backreference .

 @Data
@Entity
@Table(name = "comments")
@EntityListeners(AuditingEntityListener.class)
public class Comments {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name="comment_id")
private Long comment_id;
@OneToOne
@JoinColumn(name = "user_id")
private Users user;
@Column(name = "description")
private String description;
@Column(name="images")
private String images;
@ManyToOne
@JoinColumn(name ="post_id" , nullable = false)
@JsonIgnoreProperties(value = { "comments" ,"hibernateLazyInitializer", "handler" }, allowSetters = true)
@JsonBackReference
private Posts post;
@Column(name="last_updated")
@LastModifiedDate
private Date lastUpdated;
}

And Your Post class should be

@Data
@Entity
@Table(name = "posts")
@EntityListeners(AuditingEntityListener.class)
public class Posts {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "post_id")
private Long post_id;
@ManyToOne
@JoinColumn(name = "user_id", nullable = false)
private Users user;
@Column(name = "description")
private String description;
@Column(name="images")
private String images;
@Column(name="tags")
private String tags;
@OneToMany(
fetch = FetchType.LAZY,
mappedBy = "post",
cascade = CascadeType.ALL,
orphanRemoval = true
)
@JsonIgnoreProperties(value = { "post" ,"hibernateLazyInitializer", "handler" }, allowSetters = true)
@JsonManagedReference
private List<Comments> comments;
@LastModifiedDate
@Column(name = "last_updated")
private Date lastUpdated;
public void addComments(Comments comment) {
this.comments.add(comment);
}
}

Also I would suggest to Use Getter and Setter annotation instead of @Data .Because Tostring() method will cause recursion also .