双向关联：多对多

最新推荐文章于 2019-12-26 15:18:57 发布

码农wind

最新推荐文章于 2019-12-26 15:18:57 发布

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分类专栏： Hibernate

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本文介绍了一个简单的Java程序，使用Hibernate框架实现教师与学生之间的多对多关系。通过定义Teacher和Student类及其映射文件，展示了如何在数据库中建立这种关系，并提供了一个测试类来演示数据的保存。

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Teacher.java

package com.domain;

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

public class Teacher {
	private Integer id;
	private String name;
	private Set<Student> students = new HashSet<Student>();
	public Integer getId() {
		return id;
	}
	public void setId(Integer 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;
	}
	
}

Student.java

package com.domain;

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

public class Student {
	private Integer id;
	private String name;
	private Set<Teacher> teachers = new HashSet<Teacher>();
	public Integer getId() {
		return id;
	}
	public void setId(Integer 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;
	}
	
}

Teacher.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.domain">

	<class name="Teacher" table="teacher">		
		<id name="id">
			<generator class="native"/>
		</id>
		<property name="name" column="name"/>
		 <set name="students" table="teacher_student">
        	<key column="teacher_id"/>
        	<many-to-many class="Student" column="student_id"/>
        </set>
	</class>
	
</hibernate-mapping>

Student.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

    <session-factory>
        <property name="connection.username">root</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate2</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.password">123456</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hbm2ddl.auto">create</property>
        <property name="show_sql">true</property>
        
        <mapping resource="com/domain/Department.hbm.xml"/>
        <mapping resource="com/domain/Employee.hbm.xml"/>
        
        <mapping resource="com/domain/Teacher.hbm.xml"/>
        <mapping resource="com/domain/Student.hbm.xml"/>
    </session-factory>

</hibernate-configuration>

测试类：

package com.junit;

import org.hibernate.Session;
import org.junit.Test;

import com.domain.Student;
import com.domain.Teacher;
import com.utils.HibernateSessionFactory;

public class ManyToMany {

	@Test
	public void add(){
		
		Teacher teacher1 = new Teacher();
		teacher1.setName("李老师");
		
		Teacher teacher2 = new Teacher();
		teacher2.setName("张老师");
		
		Student student1 = new Student();
		student1.setName("张三");
		student1.getTeachers().add(teacher1);
		student1.getTeachers().add(teacher2);
		
		Student student2 = new Student();
		student2.setName("李四");
		student2.getTeachers().add(teacher1);
		student2.getTeachers().add(teacher2);
		
//		teacher1.getStudents().add(student1);
//		teacher1.getStudents().add(student2);
//		
//		teacher2.getStudents().add(student1);
//		teacher2.getStudents().add(student2);
		
		Session session = HibernateSessionFactory.getSession();
		session.beginTransaction();
		
		session.save(teacher1);
		session.save(teacher2);
		session.save(student1);
		session.save(student2);
		
		session.getTransaction().commit();
		HibernateSessionFactory.closeSession();
	}
}