Spring+Hibernate:无法删除单向关系中的子级

Question

我试着在这里找到类似的问题，我在这里找到了这个，但它没有太大的帮助。

这正是我的问题所在。问题是@ondelete迫使我建立双向关系，对吗？如果可能的话，我想保持单向性。

java.sql.SQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`blogapp2`.`post_comments`, CONSTRAINT `FKrvgf8o4dg5kamt01me5gjqodf` FOREIGN KEY (`comments_id`) REFERENCES `comment` (`id`))

  @GetMapping("/dashboard/showposts/deletecomment/{id}")
    public String deleteComment(@PathVariable("id") Long id) {
        commentService.deleteComment(id);
        return "redirect:/admin/dashboard/showposts";
    }

 @OneToMany(cascade = CascadeType.ALL)
    private List<Comment> comments = new ArrayList<>();

L.E：我修改了我的处理程序方法，看起来像这样

 @GetMapping("/dashboard/showposts/deletecomment/{id}")
    public String deleteComment(@PathVariable("id") Long id) {
        List<Comment> comments = commentService.findAll();
        Comment comment = commentService.findBYId(id);
        comments.remove(comment);
        return "redirect:/admin/dashboard/showposts";
    }

Answer 1

你可以在不创建双向关系的情况下这样做，但在这样做时有一个警告，我稍后会讲到这一点，让我们看看如何在单向关系中做到这一点。

首先，您需要在实体关系上指定orphanremoval=true

@OneToMany(cascade = { CascadeType.ALL }, orphanRemoval = true)
List<Comment> comments = new ArrayList();

// Now I am assuming you have equals and hash code methods are implemented in your comment class,

// So all you need to load the Comment Entity by its id and then have to call

Comment comment = dao.findById(id);
comments.remove(comment);

// This will delete the comment from table and will keep all comments as it is.

// Another way is to iterate the comments list and find matching Comment object (add the method in transaction)

@Service
class PostService {

    @Transactional
    public Comment deleteComment(Integer commentId) {
       Post post = repository.findById(id);
       List<Comment> comments = post.getComments();
       Comment comment = comments.stream().filter(c -> c.getId().equals(commentId)).findAny()
     .orElseThrow(() -> new IllegalArgumentException("Invalid comment id"));
      
      comments.remove(comment);

      return comment;
    }

}

 

注意事项：

1. post.getComments() // will load all comments from database
2. comments.remove(comment) // will trigger additional INSERT statements

然后它将从注释表中删除该条目，因此这是使用单向关系必须付出的性能代价。