Question

我不确定使用JPA建立一对一关系时会缺少什么。

第二个表中的字段username_id被创建为MUL密钥，我期待外键，这是怎么回事？

@Entity
@Table(name="userandpassword")
public class LoginAndPassword {

    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    private Long username_id;

    @Column(name = "username")
    private String username;

    @Column(name = "user_password")
    private String user_password;

    @OneToMany(cascade = CascadeType.ALL)
    List<GradeEntity> g;

//getters, setters

@Entity
@Table(name = "grades")
public class GradeEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "grade")
    private String grade;

    @Column(name = "comment")
    private String comment;

    @ManyToOne
    @JoinColumn(name= "username_id")
    private LoginAndPassword loginAndPassword;

//getters,setters

Answer 1

您需要在@OneToMany

中添加mappedBy

 @OneToMany(cascade = CascadeType.ALL, mappedBy = "loginAndPassword")
 List<GradeEntity> g;

Answer 2

基本上，您需要指定

@OneToMany(mappedBy = "loginAndPassword", cascade = CascadeType.ALL)
List<GradeEntity> g;

这是一个很好的教程，解释了JPA和Hibernate OneToMany关系映射，我强烈建议您检查一下。

JPA and Hibernate One To Many Relationship Mapping Example with Spring Boot and MySQL

如何在JPA中实现一对多关系

2 个答案: