java - Hibernate 添加到 List 时重新创建连接表

Question

我有一个包含 Comment 列表的 Story，用 JoinTable 映射。我注意到每次我向列表中添加新评论时，hibernate 都会删除并重新创建连接表中与故事相关的所有条目。我希望它只是向表中添加一个新行。在下面的代码中，保存方法由 Spring Data 实现。我错过了什么吗？谢谢。

故事.java:

@Entity
public class Story implements Serializable {
    @OneToMany
    @JoinTable(name="UserComment", joinColumns = @JoinColumn(name = "Story_id"), inverseJoinColumns = @JoinColumn(name = "Comment_id"))
    private List<Comment> userComments;
    ...

注释.java:

@Entity
public class Comment implements Serializable {
...

添加新评论:

Comment comment = new Comment();
comment.setContent(content);
commentRepository.save(comment);
story.getUserComments().add(comment);
storyRepository.save(story);

Hibernate 记录 storyRepository.save(story) 执行:

Hibernate: delete from UserComment where Story_id=?
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)
Hibernate: insert into UserComment (Story_id, Comment_id) values (?, ?)

库版本:

• hibernate 4.3.5
• Spring 数据 JPA 1.6.0

Answer 1

这是所用单向包的预期行为。根据 [Hibernate 反模式][1]:

The bag semantics has the worst performance when it comes to the number of operations since it always re-creates the entire collection. Hibernate issues a delete statement to remove all associations of the old collection from the association table. Then, it issues N inserts to add all associations representing the new collection to the association table. Hibernate does not analyze how many elements have been changed in the collection.

1. 您可以通过将它变成一个 id-bag 来优化它，它是一个索引列表。
2. 您可以将具有 2 个@ManyToOne 关联的 UserComment 映射映射到 Story 和 Comment，因此您的包将变成一个 mappedBy 双向包，这比它的单向对应包更有效(因为 mappedBy 包不会控制关联，因为它将是@ManyToOne 端将状态转换传播到 SQL 语句)。