jpa 多表关联，头痛，求大佬指点

之前用的 mybatis，各种查询都是自己写，非常快捷

最近开始练习使用 jpa

涉及到多表关联，用起来有点头痛

我写了一个 demo,涉及 3 张表，学生,老师，学生-老师关联表

Student

@Entity
@Table
@Data
public class Student {

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

    @Column(length = 32)
    private String name;

    @JoinTable(name = "student_and_teacher",
            joinColumns = {@JoinColumn(name = "studentId", referencedColumnName = "id")},
            inverseJoinColumns = {@JoinColumn(name = "teacherId", referencedColumnName = "id")},
            foreignKey = @ForeignKey(name = "none", value = ConstraintMode.NO_CONSTRAINT),
            inverseForeignKey = @ForeignKey(name = "none", value = ConstraintMode.NO_CONSTRAINT))
    @ManyToMany
    private List<Teacher> teachers;



}

其中的 @JoinTable 就是表明要关联到学生-老师关联表中去

Teacher 类

@Entity
@Table
@Data
public class Teacher {

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

    @Column(length = 32)
    private String name;


}

然后就是学生-老师关联

student-teacher

@Entity
@Table(name = "teacher_and_lesson")
@Data
public class StudentAndTeacher {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column
    private Long studentId;

    @Column
    private Long teacherId;
}

这一套工作的很好，可以查询出学生-老师关系，添加一些数据后，执行查询学生的方法，可以得到

{"id":1,"name":"Joe","teachers":[{"id":1,"name":"王老师"},{"id":2,"name":"李老师"}]}

但是，这个时候，我想增加一个课程表，设定每个老师教一个课程

Lesson

@Entity
@Table
@Data
public class Lesson {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(length = 32)
    private String name;
}

然后，就是增加老师-课程关联关系

TeacherAndLesson

@Entity
@Table
@Data
public class TeacherAndLesson {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column
    private Long lessonId;

    @Column
    private Long teacherId;
}

这样的话，就需要在老师实体类中，增加一个课程的关联关系


@Entity
@Table
@Data
public class Teacher {

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

    @Column(length = 32)
    private String name;

    @JoinTable(name = "teacher_and_lesson",
            joinColumns = {@JoinColumn(name = "teacherId", referencedColumnName = "id")},
            inverseJoinColumns = {@JoinColumn(name = "lessonId", referencedColumnName = "id")},
            foreignKey = @ForeignKey(name = "none", value = ConstraintMode.NO_CONSTRAINT),
            inverseForeignKey = @ForeignKey(name = "none", value = ConstraintMode.NO_CONSTRAINT))
    @OneToOne
    private Lesson lesson;

}

这样写了之后，程序启动完成，自动创建的 teacher_and_lesson 表中，会多出一个 student_id 出来，

没搞懂是为啥。😭

求大佬指点，谢谢。。。