JPA如何在@OneToMany关系的列上添加唯一约束如用户名 [英] JPA How add unique contraint on column for @OneToMany relation like on username

问题描述

我有一个代表网站的Site类和一个User类. Site可以具有多个User.

I have a Class Site that represents a website and a Class User. A Site can have multiple Users.

class Site {

    private int site_ID;

    @OneToMany // with a join table
    private List<User> users;
    // ...
}

class User {

    private int user_ID;

    private String name;

    private String lastname;

    private String username;

    private String password;

}

我想在所有站点上都允许使用相同的用户名，但是每个站点只能使用一个用户名.

I want to allow same username to exist on all Sites, but only one by site.

Site/User/username
1   /1   /username1
1   /2   /username2
2   /3   /username1

我该怎么做?

推荐答案

让用户获得站点引用:

@ManyToOne(optional=false)
private Site site;

现在将约束添加到用户:

Now add the constraint to user:

@Table(uniqueConstraints = {
    @UniqueConstraint(columnNames = { "username", "site" }))
} @Entity
public class User{
// etc
}

您还必须更改站点映射:

You will also have to change the Site mapping:

@OneToMany(mappedBy="site")
private List<User> users;

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