Save successful but Update failed - Many to Many Spring JPA with extra column using Jointable

Question

Am getting an error while updating the existing entity with below approach using PostRepository save method.

Here are my objects,

@Entity
public class Post {
  @Id
  private String postId;
  private String postName;
  @OneToMany(mappedBy = "Post", cascade = CascadeType.ALL)
  private Collection<PostTag> postTags = new HashSet<PostTag>();
}

@Entity
public class Tag {
  @Id
  private String tagId;
  private String tagName;
  @OneToMany(mappedBy = "tag", cascade = CascadeType.ALL)
  @JsonIgnore
  private Collection<PostTag> postTags = new HashSet<PostTag>();
}

@Entity
public class PostTag {
  @EmbeddedId
  private PostTagId postTagId = new PostTagId();
  
  @ManyToOne
  @MapsId("postId")
  @JoinColumn(name = "post_Id")
  @JsonIgnore
  private Post post;
  
  @ManyToOne
  @MapsId("tagId")
  @JoinColumn(name = "tag_Id")
  private Tag tag;
  
  //extra columns ommited
}


@Embeddable
public class PostTagId implements Serializable {
  private String postId;
  private String tagId;
  //equals & hashcode ommited
}

I try to save the post as in the form of below POST json,

{
  "postId": "post-001",
  "postName": "post-001",
  "postTags": [
    {
      "tag": {
        "tagId": "tag-001",
        "tagName": "tag-001"
      }
    }
  ]
}

Service implementation looks as below,

public Post save(Post post){
    Post newPost = new Post();
    newPost.setPostName(Post.getPostName());
    newPost.setPostId(Post.getPostId());
    for (PostTag posttag : post.getPostTags()) {
      PostTag newPostTag = new PostTag();
      Tag dbTag = tagRepo.getById(posttag.getTag().getTagId());
      if(dbTag == null){
        Tag newtag = new Tag();
        newtag.setTagId(posttag.getTag().getTagId());
        newtag.setTagName(posttag.getTag().getTagName());
        tagRepo.save(newTag);
        dbTag = newTag;
      }
      newPostTag.setTag(dbTag);
      newPostTag.setPost(newPost);
      newPost.getPostTags().add(newPostTag);
    }
    return PostRepository.save(newPost);
}

The above code works first time and creates record in POST & TAG & POSTTAG. But when i run the save again with same input it complains below error,

javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [PostTagId@c03f34a0]

Clearly it says there is already an obj which is there in PostId + TagId combination, But how can i just do update or merge in that case for only PostTag entity extra fields if there is already same combination available?

Please help.

Answer 1

There was already same question on next link, so it maybe helps you: answer