hibernate-----many-to-many

hibernate:many-to-many

以学生和老师为例
建表语句：

CREATE DATABASE `manytomany`
CHARACTER SET 'utf8';

USE `manytomany`;

DROP TABLE IF EXISTS `student`;
create table student(
	sid int auto_increment primary key,
	name varchar(10) not null
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
DROP TABLE IF EXISTS `teacher`;
create table teacher(
	tid int auto_increment primary key,
	name varchar(10) not null
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
DROP TABLE IF EXISTS `st`;
create table st(
	sid int not null,
	tid int not null
)ENGINE=InnoDB DEFAULT CHARSET=utf8;

Teacher.java

package com.test.domain;

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

public class Teacher implements java.io.Serializable {

	private Integer tid;

	private String name;
	
	private Set students = new HashSet();
	
	public Teacher() {
	}

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

	public Integer getTid() {
		return this.tid;
	}

	public void setTid(Integer tid) {
		this.tid = tid;
	}

	public String getName() {
		return this.name;
	}

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

	public Set getStudents() {
		return students;
	}

	public void setStudents(Set students) {
		this.students = students;
	}
	
	

}

Student.java:

package com.test.domain;

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

public class Student implements java.io.Serializable {

	private Integer sid;

	private String name;
	
	private Set teachers = new HashSet();

	public Student() {
	}

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

	public Integer getSid() {
		return this.sid;
	}

	public void setSid(Integer sid) {
		this.sid = sid;
	}

	public String getName() {
		return this.name;
	}

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

	public Set getTeachers() {
		return teachers;
	}

	public void setTeachers(Set teachers) {
		this.teachers = teachers;
	}

	
}

Teacher.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.test.domain.Teacher" table="teacher" catalog="manytomany">
        <id name="tid" type="java.lang.Integer">
            <column name="tid" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" length="10" not-null="true" />
        </property>
        <!--inverse="false": 由teacher操作student -->
        <set name="students" table="st" cascade="save-update" inverse="false">
        	<key column="tid"></key>
        	<many-to-many class="com.test.domain.Student" column="sid">
        	</many-to-many>
        </set>
    </class>
</hibernate-mapping>

Student.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.test.domain.Student" table="student" catalog="manytomany">
        <id name="sid" type="java.lang.Integer">
            <column name="sid" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" length="10" not-null="true" />
        </property>
        <!--inverse="true": 由teacher操作student -->
        <set name="teachers" table="st" cascade="save-update" inverse="true">
        	<key column="sid"></key>
        	<many-to-many class="com.test.domain.Teacher" column="tid">
        	</many-to-many>
        </set>
    </class>
</hibernate-mapping>

测试类,Test.java

package com.test.dao;

import org.hibernate.Session;

import com.test.domain.Student;
import com.test.domain.Teacher;

public class Test {

	public static void main(String[] args) {
		Session session = HibernateSessionFactory.getSession();
		
		Teacher teacher1 = new Teacher();
		teacher1.setName("teacher1");
		
		Teacher teacher2 = new Teacher();
		teacher2.setName("teacher2");
		
		Teacher teacher3 = new Teacher();
		teacher3.setName("teacher3");
		
		Student student1 = new Student();
		student1.setName("student1");
		
		Student student2 = new Student();
		student2.setName("student2");
		//student1.getTeachers().add(teacher1);student1.getTeachers().add(teacher2);student2.getTeachers().add(teacher1);这几句代码可以不要，因为Teacher掌握主动权。所以下面几句代码给注释掉了
//		//学生一有2个老师
//		student1.getTeachers().add(teacher1);
//		student1.getTeachers().add(teacher2);
//		
//		//学生二有一个老师
//		student2.getTeachers().add(teacher1);
		
		//因为老师是inverse="false" ,老师掌握主动权
		//第一个老师有2个学生
		teacher1.getStudents().add(student1);
		teacher1.getStudents().add(student2);
		
		//第二个老师有一个学生
		teacher2.getStudents().add(student1);
		
		session.saveOrUpdate(teacher1);
		session.saveOrUpdate(teacher2);
		session.beginTransaction().commit();
		session.close();
		
		/**执行的sql
		Hibernate: insert into manytomany.teacher (name) values (?)
		Hibernate: insert into manytomany.student (name) values (?)
		Hibernate: insert into manytomany.student (name) values (?)
		Hibernate: insert into manytomany.teacher (name) values (?)
		Hibernate: insert into st (tid, sid) values (?, ?)
		Hibernate: insert into st (tid, sid) values (?, ?)
		Hibernate: insert into st (tid, sid) values (?, ?)
		*/
		
	}

}