如何让jpa休眠创建具有多对一但没有外键的实体

Question

我有两个具有多对一关系的表，但它们没有外键。 就像Student 很多，而Teacher 就是其中之一，

例如实体：

@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;
}

当我查询学生时，sql是：

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

我发现@ManyToOne 不起作用，它看起来需要一个外键。但是该表无法提供此类信息。

谁能告诉我如何配置实体？

Answer 1

您必须使用以下映射：

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 如果您想保留当前映射，那么您需要在 hql 中使用“旧”样式的连接来实现非外键列的连接：

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