如何spring jpa hibernate創建多對一但沒有外鍵的實體

Question

我有兩個具有多對一關系的表，但它們沒有外鍵。 就像Student很多，而Teacher是一個，

實體例如：

@Entity
@Table(name = "student")
class Student {


   @Column(name = "TeacherName")
   private String teacherName;

   @ManyToOne
   private Teacher teacher
}


@Entity
@Table(name = "teacher")
class Teacher {

 private String name;
}

當我查詢學生時，sql 是：

select * from Student as st INNER JOIN Teacher as tcr ON st.TeacherName = tcr.name;

我發現@ManyToOne不能工作，看起來它需要一個外鍵。 表不能提供這樣雖然。

有人能告訴我如何配置實體嗎？

Answer 1

您必須使用以下映射：

public class Teacher  {

    @OneToMany(mappedBy = "teacher")
    private Set<Student> students;

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

public class Student {
    @ManyToOne
    @JoinColumn(name = "teacherName", referencedColumnName = "name")
    private Teacher teacher;

}

然后在 HQL 中：

select s from Student s INNER JOIN s.teacher t where t.name = :name 

或者，如果您想保留當前的映射，那么您需要使用 hql 中的“舊”連接樣式來實現非外鍵列的連接：

select s from Student s, Teacher t where t.name = s.teacherName and t.name = :name