Many-To-Many （学生、课程、分数）

最新推荐文章于 2025-11-21 11:54:14 发布

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本文介绍了如何使用Java实现学生、课程及分数之间的多对多关系管理。通过建立Student、Course和Score三个实体类，利用注解定义了这些实体类间的关联关系。特别地，文章详细解释了如何使用JPA（Java Persistence API）的@ManyToMany、@JoinTable和@ManyToOne注解来维护多对多的关系。

[align=center][size=xx-large][color=red][b]Many-To-Many （学生、课程、分数）[/b][/color][/size][/align]
[color=red]多对多：[/color]
一个学生可以选多门课
一门课可以被多个学生选修

[color=red]多对一：[/color]
多组分数对应一个学生
多组分数对应一门课程

[color=red]多对多要有三张表[/color] 分别为：[color=red]student、course、sorce[/color]
[color=red]一、Student.java[/color]


import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;

@Entity
public class Student {
	private int id;
	private String name;
	private Set<Course> courses = new HashSet<Course>();

	@ManyToMany
         //设置第三张表score与student和course表之间的外键连接，操作其中两张表的数据时，成绩表数据也会被操作
	@JoinTable(name="score",
		joinColumns=@JoinColumn(name="student_id", referencedColumnName="id"),
		inverseJoinColumns=@JoinColumn(name="course_id", referencedColumnName="id")
		)
	public Set<Course> getCourses() {
		return courses;
	}
	public void setCourses(Set<Course> courses) {
		this.courses = courses;
	}
	@Id
	@GeneratedValue
	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;
	}

}

[color=red]二、Course.java[/color]


import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Course {
	private int id;
	private String name;
	@Id
	@GeneratedValue
	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;
	}

}

[color=red]
三、Score.java[/color]



import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="score")
public class Score {
	private int id;
	private int score;
	private Student student;
	private Course course;
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public int getScore() {
		return score;
	}
	public void setScore(int score) {
		this.score = score;
	}
	@ManyToOne
	@JoinColumn(name="student_id")
	public Student getStudent() {
		return student;
	}
	public void setStudent(Student student) {
		this.student = student;
	}

	@ManyToOne
	@JoinColumn(name="course_id")
	public Course getCourse() {
		return course;
	}
	public void setCourse(Course course) {
		this.course = course;
	}

}