持久列表关系spring数据mongodb

Question

What's wrong, I tried to add new comment to comments list, the comment is mapped as list on Post class.

Here's my code.

Post.java

@Document
public class Post {

    @Id
    private String id;

    @DBRef
    private List<Comment> comments;

    public void addComment(Comment comment) {
    if (comments == null) {
        comments = new ArrayList<>();
    }
    this.comments.add(comment);
    }
    // getters and setters....
}

Comment.java

@Document
public class Comment {

    @Id
    private String id;
    private String comment;
    private int rating;

    // getters and setters....
}

Test.class

@Test
public void savePostWithComments() {
    Post post = postRepository.findAll().get(1);

    Comment comment = new Comment();
    comment.setComment("comment");
    comment.setRating(5);

    post.addComment(comment);
    postRepository.save(post);
}

The test fail with this error

org.springframework.data.mapping.model.MappingException: Cannot create a reference to an object with a NULL id.

All help appreciated !

Answer 1

Referencing to spring-data-mongodb docs

Important The mapping framework does not handle cascading saves. If you change an Account object that is referenced by a Person object, you must save the Account object separately. Calling save on the Person object will not automatically save the Account objects in the property accounts.

Adding

commentRepository.save(comment);

before persisting Post object reslove the problem