保存成功但更新失败 - 多对多 Spring JPA 使用 Jointable 额外列

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