hibernate 单向多对多关联映射练习

hibernate多对多关联关系映射
多个teacher对应多个student
由于多对多关系必须借助关联表来表达关联关系，所以多对多关系只有两种情况：一是带关联表的双向多对对映射，另一种是带关联表的单向多对多映射。
Teacher.java

package com.aabnn.vo;

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

public class Teacher {
	private int id;
	private String name;
	private Set<Student> students=new HashSet<Student>();
	public int getId() {
		return id;
	}
	public Teacher(){
		
	}
	public Teacher(String name,Set<Student> students){
		this.name=name;
		this.students=students;
	}
	@SuppressWarnings("unused")
	private 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;
	}
}

Student.java

package com.aabnn.vo;

public class Student {
	private int id;
	private String name;
	public Student(){}
	public Student(String name){
		this.name=name;
	}
	public int getId() {
		return id;
	}
	
	@SuppressWarnings("unused")
	private void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

HibernateUtil.java

package com.aabnn.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
	private static SessionFactory sf;
	static{
		sf=new Configuration().configure().buildSessionFactory();
	}
	public static SessionFactory getSessionFactory(){
		return sf;
	}
}

Test.java

package com.aabnn.test;

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

import org.hibernate.Transaction;
import org.hibernate.classic.Session;

import com.aabnn.util.HibernateUtil;
import com.aabnn.vo.Student;
import com.aabnn.vo.Teacher;

public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Session sess=HibernateUtil.getSessionFactory().openSession();
		Transaction tx=sess.beginTransaction();
		try{
			Student s1=new Student("xiaojian");
			Student s2=new Student("wangpeng");
			Student s3=new Student("hongsheng");
			Set<Student> students=new HashSet<Student>();
			students.add(s1);
			students.add(s2);
			students.add(s3);
			Teacher t1=new Teacher("wangshuang",students); 
			sess.persist(t1);
			tx.commit();
		}catch(Exception e){
			tx.rollback();
		}finally{
			HibernateUtil.getSessionFactory().close();
		}
	}

}

hibernate.cfg.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">

<hibernate-configuration>
	<session-factory>
	<!--mysql connection  -->
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/mytest</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">root</property>
		<!--c3p0 connection pool  -->
		<property name="hibernate.c3p0.max_size">20</property>
		<property name="hibernate.c3p0.min_size">2</property>
		<property name="hibernate.c3p0.max_statements">100</property>
		<property name="hibernate.c3p0.idle_test_period">3000</property>
		<property name="hibernate.c3p0.acquire_increment">2</property>
		<property name="hibernate.c3p0.validate">true</property>
		<!-- mysql dialect -->
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>
		<property name="hibernate.show_sql">true</property>
		<mapping resource="com/aabnn/vo/Teacher.hbm.xml" />
		<mapping resource="com/aabnn/vo/Student.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

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.aabnn.vo">

	<class name="Teacher" table="teacher">
		<comment>先映射主键</comment>
		<id name="id" column="id">
			<generator class="identity" />
		</id>	
		<property name="name" type="string" column="name" />
		<set name="students" table="teacherstudent" cascade="save-update">
			<key column="teacherid" />
			<many-to-many class="Student" column="studentid" />
		</set>
	</class>
	<!--name 的值是Teacher类集合属性，table值是关联表，cascade值是在操作数据库是否级联.-->
	<!-- key值是关联表的外键 -->
	<!--many-to-many 描述关联表。-->
</hibernate-mapping>

Student.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.aabnn.vo">

	<class name="Student" table="student">
		<comment>先映射主键</comment>
		<id name="id" column="id">
			<generator class="identity" />
		</id>	
		<property name="name" type="string" column="name" />
	</class>
	
</hibernate-mapping>

mysql archive

 create database mytest;  
 create table teacher(  
 id integer unsigned not null auto_increment,  
 name varchar(45),  
 primary key(id));  
 create table student(  
 id integer unsigned not null auto_increment,  
 name varchar(45),  
 primary key(id));  
 create table teacher_student(  
 teacherid integer unsigned not null,  
 studentid integer unsigned not null,  
 primary key(teacherid,studentid));