java如何在JPA（Hibernate）中映射一对多关系和复合主键？

Question

我的桌子是这样的：

School
-------
school_id (pk)
...

Student
school_id (pk) (fk)
student_id (pk)
...

因此，使用JPA（Hibernate），我尝试了类似的方法

@Entity
@Table("SCHOOL")
public School {
    @Column(name = "SCHOOL_ID")
    private String schoolId;
    
    @OneToMany
    private List<Student> students;
}

@Entity
@Table("STUDENT")
public Student {
    @EmbeddedId
    private StudentPK studentPK;

    @ManyToOne
    @JoinColumn(name = "SCHOOL_ID")
    private School school; 
}

@Embeddable
public StudentPK implements Serializable {
    @Column(name = "SCHOOL_ID")
    private String schoolId;

    @Column(name = "STUDENT_ID"
    private String studentId;
}

当我这样做时，我经常会收到一个错误，表明在运行时违反了外键约束。我怀疑JPA试图生成一个名为“SCHOOL_ID”的新外键，而不是使用我的组合键中的现有列，但我不确定如何强制它使用现有列

Answer 1

这些关系的映射方式应该有所不同：

@Entity
@Table("SCHOOL")
public School {
    @Column(name = "SCHOOL_ID")
    private String schoolId;
    
    @OneToMany(mappedBy="school")
    private List<Student> students;
}

@Entity
@Table("STUDENT")
public Student {
    @EmbeddedId
    private StudentPK studentPK;

    @ManyToOne
    @MapsId("schoolId")
    private School school; 
}

@Embeddable
public StudentPK implements Serializable {
    @Column(name = "SCHOOL_ID")
    private String schoolId;

    @Column(name = "STUDENT_ID"
    private String studentId;
}

注意School.students上的@OneToMany.mappedBy属性和Student.school上的@MapsId注释

第2.4.1节JPA 2.2 spec中讨论了派生恒等式（带有示例）