JPA/Hibernate 中实体化连接表处理复杂多对多及多实体关系

import java.io.Serializable;
import javax.persistence.Embeddable;

@Embeddable
public class CourseRatingKey implements Serializable {

    private Long studentId;
    private Long courseId;

    // 必须提供默认构造函数
    public CourseRatingKey() {}

    public CourseRatingKey(Long studentId, Long courseId) {
        this.studentId = studentId;
        this.courseId = courseId;
    }

    // getters and setters
    public Long getStudentId() {
        return studentId;
    }

    public void setStudentId(Long studentId) {
        this.studentId = studentId;
    }

    public Long getCourseId() {
        return courseId;
    }

    public void setCourseId(Long courseId) {
        this.courseId = courseId;
    }

    // 必须重写 equals 和 hashCode 方法
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        CourseRatingKey that = (CourseRatingKey) o;
        return studentId.equals(that.studentId) &&
               courseId.equals(that.courseId);
    }

    @Override
    public int hashCode() {
        return java.util.Objects.hash(studentId, courseId);
    }
}

import javax.persistence.*;

@Entity
@Table(name = "course_rating") // 假设数据库表名为 course_rating
public class CourseRating {

    @EmbeddedId
    CourseRatingKey id; // 使用 @EmbeddedId 引用复合主键类

    @ManyToOne
    @MapsId("studentId") // 将复合主键中的 studentId 映射到 Student 实体的主键
    @JoinColumn(name = "student_id") // 对应数据库中的外键列名
    Student student;

    @ManyToOne
    @MapsId("courseId") // 将复合主键中的 courseId 映射到 Course 实体的主键
    @JoinColumn(name = "course_id") // 对应数据库中的外键列名
    Course course;

    @Column(name = "rating")
    int rating; // 连接表特有的额外属性

    // 必须提供默认构造函数
    public CourseRating() {}

    public CourseRating(Student student, Course course, int rating) {
        this.student = student;
        this.course = course;
        this.rating = rating;
        this.id = new CourseRatingKey(student.getId(), course.getId());
    }

    // standard getters and setters
    public CourseRatingKey getId() {
        return id;
    }

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

    public Student getStudent() {
        return student;
    }

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

    public Course getCourse() {
        return course;
    }

    public void setCourse(Course course) {
        this.course = course;
    }

    public int getRating() {
        return rating;
    }

    public void setRating(int rating) {
        this.rating = rating;
    }
}

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

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

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

    @OneToMany(mappedBy = "student", cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<CourseRating> ratings = new HashSet<>();

    // standard constructors, getters, and setters
    public Student() {}

    public Student(String name) {
        this.name = name;
    }

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Set<CourseRating> getRatings() {
        return ratings;
    }

    public void setRatings(Set<CourseRating> ratings) {
        this.ratings = ratings;
    }

    // Helper method to add rating
    public void addRating(CourseRating rating) {
        ratings.add(rating);
        rating.setStudent(this);
    }

    public void removeRating(CourseRating rating) {
        ratings.remove(rating);
        rating.setStudent(null);
    }
}

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

@Entity
@Table(name = "course")
public class Course {

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

    @OneToMany(mappedBy = "course", cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<CourseRating> ratings = new HashSet<>();

    // standard constructors, getters, and setters
    public Course() {}

    public Course(String title) {
        this.title = title;
    }

    public Long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Set<CourseRating> getRatings() {
        return ratings;
    }

    public void setRatings(Set<CourseRating> ratings) {
        this.ratings = ratings;
    }

    // Helper method to add rating
    public void addRating(CourseRating rating) {
        ratings.add(rating);
        rating.setCourse(this);
    }

    public void removeRating(CourseRating rating) {
        ratings.remove(rating);
        rating.setCourse(null);
    }
}

// 复合主键类 (与 @EmbeddedId 示例中的 CourseRatingKey 类似，但通常字段类型与实体中的主键字段类型一致)
public class CourseRatingId implements Serializable {
    private Long student; // 字段名需要与 CourseRating 实体中作为主键的字段名匹配
    private Long course;  // 字段名需要与 CourseRating 实体中作为主键的字段名匹配

    // constructors, equals, hashCode
}

@Entity
@IdClass(CourseRatingId.class)
public class CourseRating {

    @Id
    @ManyToOne
    @JoinColumn(name = "student_id")
    private Student student; // 这里的字段名 "student" 对应 CourseRatingId 中的 "student"

    @Id
    @ManyToOne
    @JoinColumn(name = "course_id")
    private Course course; // 这里的字段名 "course" 对应 CourseRatingId 中的 "course"

    private int rating;

    // getters and setters
}