hibernate - 如何在spring boot data jpa中链接@Entity之间的外键

Question

技术:

1. MySQL 8
2. spring-boot-starter-parent 2.3.3.RELEASE
3. 使用 spring-boot-starter-data-jpa

错误:

nested exception is org.springframework.dao.DataIntegrityViolationException: **could not execute statement; SQL [n/a]; constraint [null];** 
java.sql.SQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`emr`.`user_detail`, CONSTRAINT `user_detail_ibfk_1` FOREIGN KEY (`id`) REFERENCES `facility` (`id`))

DDL:

create table facility
(
    id INTEGER PRIMARY KEY AUTO_INCREMENT,
    name varchar(60),
    address varchar(200)
);
    
create table user_detail
(
    id INTEGER PRIMARY KEY AUTO_INCREMENT,
    username varchar(20) not null unique,
    contactNo varchar(12),
    facilityId int unsigned
    foreign key (id) references facility(id)
);

Java 类:

@Entity
@Table(name= "user_detail")
public class User {
    
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    private String username;

    @Column (name="contactNo")
    private String contactNo;
        
    @Column (name="facilityId")
    private Integer facilityId;
    
    //getter and setter
}
    
@Entity
@Table(name="facility")
public class Facility {
    
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    private String name;
}

假设 facility 表有 1 行 Id=1 和 name='Facility 1'我正在尝试在 user_detail 表中为 facilityId=1 插入一行，但收到​​错误消息

据我所知，无法找到 facilityId 是 Facility.java 中的字段 id 并假设 null user_detail.facilityId 列中不允许的值

我完全无法让代码理解 id 是外键字段。尝试了 @JoinColumn 的一些组合但没有成功。

Answer 1

异常表明，当您尝试保存 User 时，它将 null 保存为 facilityId。

要完成这项工作，您需要将设施指定为用户实体中的另一个表(您做错了)。

@Entity
@Table(name= "user_detail")
public class User {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    private String username;
    @Column (name="contactNo")
    private String contactNo;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "facilityId", referencedColumnName = "id")
    private Facility facility;
    
    //getter and setter
}

根据您的要求，您需要指定关系。看来这里的关系应该是一对一的，所以我就这样标记了。