Question

当我查询与另一个实体有OneToOne关系的实体时，我遇到了问题。这是场景：

数据库表：

create table people (
    id decimal(10,0) NOT NULL,
    email varchar(512) NOT NULL
);

create table users (
    email varchar(512) NOT NULL
);

测试数据：

insert into users (email) values ('jhon@domain.com');
insert into users (email) values ('mary@domain.com');

insert into people (id, email) values (1, 'jhon@domain.com');
insert into people (id, email) values (2, 'mary@domain.com');

实体：

@Entity(name = "people")
public class Person implements Serializable {

    @Column
    @Id
    private long id;

    @Column
    private String email;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

}

@Entity(name = "tbl_users")
public class User implements Serializable {

    @Id
    private String email;

    @OneToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    @JoinColumn(name = "email", referencedColumnName = "email")
    private Person person;

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

调用：

...
User user = entityManager.find(User.class, "jhon@domain.com");
...

在de调用之后，hibernate的日志显示：

select user1_.email as email2_0_, person2_.id as id1_1_, person2_.email as email1_1_
from users user1_ left outer join people person2_ on user1_.email=person2_.id
where user1_.email=?

正如您所看到的，连接错误是因为将users.email与people.id（ user1_.email = person2_.id ）进行比较，因此它返回用户没有相应的人。

关于如何修复它的任何想法？

非常感谢!!

Answer 1

我认为您应该重新考虑您的数据模型。 User和Person之间的关系看起来更像是继承。

对于你的映射问题，他们会在这里看到进一步的讨论：

JPA providers: why do relationships/FKs to non-PK columns work in Hibernate and EclipseLink?

Does the JPA specification allow references to non-primary key columns?

Answer 2

严格来说，the JPA specification does not allow references to non-primary key columns。它可能适用于某些JPA实现，但它不合适。

但是，我认为你可以通过使关系双向，并由非主键的一方拥有来实现这一点：

@Entity
public class Person {

    @Id
    private long id;

    @OneToOne
    @JoinColumn(name = "email")
    private User user;

    public String getEmail() {
        return user.getEmail();
    }

    public void setEmail(String email) {
        // left as an exercise for the reader
    }

}

@Entity
public class User {

    @Id
    private String email;

    @OneToOne(mappedBy = "user")
    private Person person;

}

我实际上并没有尝试过，所以告诫hackor 。

非主键列的OneToOne关系

2 个答案: