@ManyToMany中间表附加字段设计

在使用@ManyToMany时,若中间表只有相应的外键字段可以直接建立两个对应的Entity 设置ManyToMany

@ManyToMany 两个表多对多关联

但若是中间表有自己的附加字段，这需要为中间表建立Entity

具体如下：

Teacher <=> Student 中间表 teacher_student 附加字段 id（自增），siteId（站点id方便批删除）

增加 Teacher <=> Student 关联时，增加新的TeacherStudent

Entity：

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

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    
    @Column(name = "name")
    private String name;
    
    @Column(name = "age")
    private int age;
    
    @ManyToMany(cascade = CascadeType.PERSIST, fetch=FetchType.LAZY)
    @JoinTable(name="teacher_student",joinColumns={@JoinColumn(name="tid")},inverseJoinColumns={@JoinColumn(name="sid")})
    private Set<Student> students;
    
    @OneToMany(mappedBy="teacher", fetch = FetchType.LAZY)
    private Set<TeacherStudent> teacherStudents;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Set<Student> getStudents() {
        return students;
    }

    public void setStudents(Set<Student> students) {
        this.students = students;
    }

    public Set<TeacherStudent> getTeacherStudents() {
        return teacherStudents;
    }

    public void setTeacherStudents(Set<TeacherStudent> teacherStudents) {
        this.teacherStudents = teacherStudents;
    }
}

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

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    
    @Column(name = "name")
    private String name;
    
    @Column(name = "age")
    private int age;
    
    @ManyToMany(cascade = CascadeType.PERSIST, fetch=FetchType.LAZY)
    @JoinTable(name="teacher_student", joinColumns={@JoinColumn(name="sid")}, inverseJoinColumns={@JoinColumn(name="tid")})
    private Set<Teacher> teachers;
    
    
    @OneToMany(mappedBy="student", fetch = FetchType.LAZY)
    private Set<TeacherStudent> teacherStudents;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Set<Teacher> getTeachers() {
        return teachers;
    }

    public void setTeachers(Set<Teacher> teachers) {
        this.teachers = teachers;
    }

    public Set<TeacherStudent> getTeacherStudents() {
        return teacherStudents;
    }

    public void setTeacherStudents(Set<TeacherStudent> teacherStudents) {
        this.teacherStudents = teacherStudents;
    }
}

中间表

@Entity
@Table(name = "teacher_student")
public class TeacherStudent {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    
    @ManyToOne(fetch = FetchType.LAZY)
    @Cascade(value = CascadeType.SAVE_UPDATE)
    @JoinColumn(name="tid")
    private Teacher teacher;
    
    @ManyToOne(fetch = FetchType.LAZY)
    @Cascade(value = CascadeType.SAVE_UPDATE)
    @JoinColumn(name="sid")
    private Student student;
    
    @JoinColumn
    private int siteId;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    public Student getStudent() {
        return student;
    }

    public void setStudent(Student student) {
        this.student = student;
    }

    public int getSiteId() {
        return siteId;
    }

    public void setSiteId(int siteId) {
        this.siteId = siteId;
    }
}