jpa OneToMany&多对一 [英] jpa OneToMany & ManyToOne

问题描述

我的模型中有一个oneToMany和ManyToOne映射:

i have a oneToMany and ManyToOne mapping in my models:

班级用户

@OneToMany (cascade = { CascadeType.REFRESH, CascadeType.DETACH }, fetch = FetchType.EAGER)
    private Set<Judgement> judgements;

班级判决

@ManyToOne(cascade = { CascadeType.REFRESH, CascadeType.DETACH})
    @JoinColumn(name = "user_id")
    private User judge;

在数据库中，我必须将表作为用户和判断"，当我尝试运行代码时，它显示错误为:

and in DB, i have to tables as Users and Judgements, when i tried to run my code, it showed error as:

Caused by: org.postgresql.util.PSQLException: ERROR: relation "users_judgements" does not exist

这是否意味着我必须手动创建表users_judgements，jpa无法自动为我创建关系? RoR可以做到...谢谢.

does that mean i have to create the table users_judgements by hand, jpa cannot automatically create the relationship for me? RoR can do it...Thanks.

推荐答案

如果您在JUDGMENT表中有来自USER表user_id的外键，则不需要其他表.那就是@JoinColumn(name ="user_id").

If you have a foreign key from USER table, user_id, in JUDGMENT table then there is no need to have another table. That will be the @JoinColumn(name = "user_id").

查看您是否缺少某些东西；我看不到任何" mappedBy "属性，在您的情况下该属性将为用户".

See if you are missing something; I can not see any "mappedBy" attribute, which will be "user" in your case.

请看一下这篇文章；该链接将带您进入第4页，并提供有关一对多关系的详细信息.值得阅读整篇文章.

Please take a look at this article; page 4 that the link will take you, give details about one-to-many relationship. It will be worth reading the whole article.

http://www. javaworld.com/javaworld/jw-01-2008/jw-01-jpa2.html?page=4

此外，同一教程的第1部分非常适合基础知识；

Also, the part 1 of the same tutorial is good for basics;

http://www.javaworld.com/javaworld/jw-01-2008/jw-01-jpa1.html

这篇关于jpa OneToMany&多对一的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！