Hibernate关联映射 --- 多对多实例分析（双向关联）

最新推荐文章于 2025-12-05 17:02:52 发布

最新推荐文章于 2025-12-05 17:02:52 发布 · 75 阅读

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#java #数据库

本文详细解析了使用Hibernate框架在Java中实现多对多关系（如教师与学生）的原理与步骤，包括实体类定义、映射文件配置以及通过测试类验证实现效果。重点介绍了多对多关系的双向关联特性及其在实际开发中的应用。

Hibernate关联映射 --- 多对多实例分析（双向关联）

一概念分析

1．多对多的经典实例（Teacher – Student）

二代码分析

1．Teacher类

package com.hbsi.domain;

import java.util.Set;

//单向一对多 Teacher 一对多 Student

public class Teacher {

private int id;

private String name;

private Set<Student> students;

public Teacher() {

super();

// TODO Auto-generated constructor stub

}

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 Set<Student> getStudents() {

return students;

}

public void setStudents(Set<Student> students) {

this.students = students;

}

2．Stduent类

package com.hbsi.domain;

import java.util.Set;

public class Student {

private int id;

private String name;

private Set<Teacher> teachers;

public Student() {

super();

// TODO Auto-generated constructor stub

}

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 Set<Teacher> getTeachers() {

return teachers;

}

public void setTeachers(Set<Teacher> teachers) {

this.teachers = teachers;

}

3．Teacher的映射文件 Teacher.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

</id>

<many-to-many class="Student" column="student_id"></many-to-many>

</set>

</class>

</hibernate-mapping>

4.Student的映射文件 Student.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

</id>

<many-to-many class="Teacher" column="teacher_id"></many-to-many>

</set>

</class>

</hibernate-mapping>

5.测试类

public class Many2Many {

public static void main(String[] args) {

// add();

query(2);

}

//保存

public static void add() {

Session session = null;

Transaction transaction = null;

try {

session = HibernateUtil.getSession();

transaction = session.beginTransaction();

// 添加

Teacher t1 = new Teacher();

t1.setName("王老师");

Teacher t2 = new Teacher();

t2.setName("李老师");

Student s1 = new Student();

s1.setName("王同学");

Student s2 = new Student();

s2.setName("李同学");

Set<Student> ss = new HashSet<Student>();

ss.add(s1);

ss.add(s2);

t1.setStudents(ss);// 告诉Hibernate老师教了那两个学生

t2.setStudents(ss);

session.save(t1);

session.save(t2);

session.save(s1);

session.save(s2);

transaction.commit();

} finally {

if (session != null) {

session.close();

}

//查询

public static void query(int id) {

Session session = null;

try {

session = HibernateUtil.getSession();

Teacher teacher = (Teacher) session.get(Teacher.class, id);

System.out.println("教室的姓名:" + teacher.getName());

System.out.println("教室的学生列表：");

Iterator<Student> iterator = teacher.getStudents().iterator();

while (iterator.hasNext()) {

Student student = iterator.next();

System.out.println(student.getName() + " ");

}

System.out.println( );

Student student = (Student) session.get(Student.class, id);

System.out.println("学生的姓名:"+student.getName());

System.out.println("学生被教的老师:");

Iterator<Teacher> iterator2 = student.getTeachers().iterator();

while(iterator2.hasNext()){

Teacher teacher2 = iterator2.next();

System.out.println(teacher2.getName()+" ");

}

System.out.println();

} finally {

if (session != null) {

session.close();

}

注：

（1）Set<Teacher> tt = new HashSet<Teacher>();

tt.add(t1);

tt.add(t2);

s1.setTeachers(tt);

s2.setTeachers(tt);

如果在测试保存的时候添加会报错，因为前边已经添加了，已经更新数据库了，再更新会报

org.hibernate.exception.ConstraintViolationException错误，所以要注意

（2）映射文件中的信息一定要写对

<many-to-many class="Student" column="student_id"></many-to-many>

</set>