一对多映射 Hibernate

Question

我试图在数据库的 Comment 表中使用帖子 id 的外键保留 6 条评论，但最后 3 条评论使用新添加的外键覆盖了前 3 条评论。

测试类：

Comments comments = new Comments("1st Comment", new Date(System.currentTimeMillis()));
Comments comments2 = new Comments("2st Comment", new Date(System.currentTimeMillis()));
Comments comments3 = new Comments("3st Comment", new Date(System.currentTimeMillis()));

ArrayList<Comments> arrayList = new ArrayList<>();
arrayList.add(comments);
arrayList.add(comments2);
arrayList.add(comments3);

// Insert Without Comment
Post post1 = new Post("1st Post", "1st Post Description", new ArrayList<Comments>(), new Date(System.currentTimeMillis()));
postReposetory.save(post1);

// Insert With Comment
Post post2 = new Post("2st Post", "2st Post Description", arrayList, new Date(System.currentTimeMillis()));
postReposetory.save(post2);

// Update (Insert Comment)
post1.setComments(arrayList);
post1.setUpdatedAt(new Date(System.currentTimeMillis()));
postReposetory.save(post1);

Answer 1

您总共创建了 3 个评论实例（因此数据库表中有 3 条记录），而不是每个帖子 3 个实例。

当您更新 post1 评论时，您会将 post2 评论作为参数，因此从 comments 到 post2 的外键将更改为 post1。

如果您希望每个帖子有 3 条评论，则总共需要 6 个评论实例（2 个帖子 * 3 条评论）。

Answer 2

发生这种情况是因为您放置了相同的注释对象，然后 hibernate 认为您想要将注释的连接从 post2 更改为 post1。

因此您必须重新构建这三个注释。

    Comments comments = new Comments("1st Comment", new Date(System.currentTimeMillis()));
    Comments comments2 = new Comments("2st Comment", new Date(System.currentTimeMillis()));
    Comments comments3 = new Comments("3st Comment", new Date(System.currentTimeMillis()));

    ArrayList arrayList = new ArrayList();
    arrayList.add(comments);
    arrayList.add(comments2);
    arrayList.add(comments3);

    // Insert With Comment
    Post post1 = new Post("1st Post", "1st Post Description", new ArrayList(), new Date(System.currentTimeMillis()));
    postReposetory.save(post1);
    
    // Insert Without Comment
    Post post2 = new Post("2st Post", "2st Post Description", arrayList, new Date(System.currentTimeMillis()));
    postReposetory.save(post2);

    // Update (Insert Comment)
    comments = new Comments("1st Comment", new Date(System.currentTimeMillis()));
    comments2 = new Comments("2st Comment", new Date(System.currentTimeMillis()));
    comments3 = new Comments("3st Comment", new Date(System.currentTimeMillis()));
    post1.setComments(List.of(comments, comments2, comments3));
    post1.setUpdatedAt(new Date(System.currentTimeMillis()));
    postReposetory.save(post1);

这样就创建了另外三个对象用于评论。