[标题]:[原]Hibernate多对多(双向)
[时间]:2009-6-19
[摘要]:Hibernate双向多对多关联。如:一个学生对应多门课程，一门课程也对应多名学生。
[关键字]:Hibernate，ORM，关联，多对多，持久化，双向，映射
[环境]:MyEclipse7，Hibernate3.2，MySQL5.1
[作者]:Winty (wintys@gmail.com) http://www.blogjava.net/wintys
[正文]:
Hibernate单向多对多关联。如:一个学生对应多门课程，一门课程也对应多名学生。本例单向关联，只考虑学生到课程的一对多关联。
1、概述
a.实体类
public class Student{
......
private Set<Course> courses;
......
}
public class Course{
......
private Set<Student> students;
......
}
b.数据库表
Student与Course各对应一张数据库表，再建一张关联表student_course (studentid,courseid)，保存多对多关联。其中，student_course表的主键为studentid与courseid的联合。
c.配置文件
Student.hbm.xml:
......
<set name="courses" table="student_course" cascade="all">
<key column="studentid" />
<many-to-many column="courseid" class="wintys.hibernate.manytomany.Course"/>
</set>
......
Course.hbm.xml:
......
<set name="students" table="student_course" inverse="true" >
<key column="courseid"/>
<many-to-many column="studentid" class="wintys.hibernate.manytomany.Student" />
</set>
......
2、实体类:
Student.java:
package wintys.hibernate.manytomany;
import java.util.Set;
/**
* @version 2009-06-19
* @author Winty (wintys@gmail.com)
*
*/
public class Student {
private Integer id;
private String name;
private Set<Course> courses;
public Student(){
}
public Student(String name){
this.name = name;
}
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<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
}
Course.java:
package wintys.hibernate.manytomany;
import java.util.Set;
/**
* @version 2009-06-19
* @author Winty (wintys@gmail.com)
*
*/
public class Course {
private Integer id;
private String name;
//实现双向"多对多"关联
private Set<Student> students;
public Course(){
}
public Course(String name){
this.name = name;
}
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;
}
}
3、数据库表:
db.sql:
CREATE TABLE student(
id int(4) NOT NULL UNIQUE,
name varchar(100),
PRIMARY KEY(id)
);
CREATE TABLE course(
id int(4) NOT NULL UNIQUE,
name varchar(100),
PRIMARY KEY(id)
);
-- 关联表
CREATE TABLE student_course(
studentid int(4) NOT NULL,
courseid int(4) NOT NULL,
PRIMARY KEY(studentid,courseid),
CONSTRAINT FK_studentid FOREIGN KEY(studentid) REFERENCES student(id),
CONSTRAINT FK_courseid FOREIGN KEY(courseid) REFERENCES course(id)
);
4、映射文件:
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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="wintys.hibernate.manytomany.Student" table="student" catalog="db">
<id name="id" type="int">
<column name="id" not-null="true"/>
<generator class="increment" />
</id>
<property name="name" />
<set name="courses" table="student_course" cascade="all">
<key column="studentid" />
<many-to-many column="courseid" class="wintys.hibernate.manytomany.Course"/>
</set>
</class>
</hibernate-mapping>
Course.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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="wintys.hibernate.manytomany.Course" table="course" catalog="db">
<id name="id" type="int">
<column name="id" not-null="true"/>
<generator class="increment" />
</id>
<property name="name" />
<!-- 实现双向"多对多"关联 -->
<set name="students" table="student_course" inverse="true" >
<key column="courseid"/>
<many-to-many column="studentid" class="wintys.hibernate.manytomany.Student" />
</set>
</class>
</hibernate-mapping>
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">
<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>
<session-factory>
<property name="connection.username">root</property>
<property name="connection.url">
jdbc:mysql://localhost:3306/db?useUnicode=true&characterEncoding=utf-8
</property>
<property name="dialect">
org.hibernate.dialect.MySQLDialect
</property>
<property name="myeclipse.connection.profile">MySQLDriver</property>
<property name="connection.password">root</property>
<property name="connection.driver_class">
com.mysql.jdbc.Driver
</property>
<property name="show_sql">true</property>
<mapping resource="wintys/hibernate/manytomany/Student.hbm.xml" />
<mapping resource="wintys/hibernate/manytomany/Course.hbm.xml" />
</session-factory>
</hibernate-configuration>
4、使用测试:
DAO.java:
package wintys.hibernate.manytomany;
import java.util.List;
public interface DAO {
public void insert();
public <T> List<T> selectAll(String hql);
}
DAOBean.java:
package wintys.hibernate.manytomany;
import java.util.List;
import java.util.HashSet;
import java.util.Set;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
/**
* @version 2009-06-19
* @author Winty (wintys@gmail.com)
*
*/
public class DAOBean implements DAO {
public void insert() {
Transaction tc = null;
try{
Course c1,c2,c3;
Student s1,s2;
Set<Course> cs1 , cs2;
c1 = new Course("Course 1");
c2 = new Course("Course 2");
c3 = new Course("Course 3");
s1 = new Student("Student 1");
s2 = new Student("Student 2");
cs1 = new HashSet<Course>();
cs2 = new HashSet<Course>();
//c2为两个集合共有
cs1.add(c1);
cs1.add(c2);
cs2.add(c2);
cs2.add(c3);
s1.setCourses(cs1);
s2.setCourses(cs2);
Session session = HibernateUtil.getSession();
tc = session.beginTransaction();
/*
在Student.hbm.xml中设置了cascade="all"，就不需要手动保存c1/c2/c3
session.save(c1);
session.save(c2);
session.save(c3);
*/
session.save(s1);
session.save(s2);
tc.commit();
}catch(HibernateException e){
try{
if(tc != null)
tc.rollback();
}catch(Exception ex){
System.err.println(ex.getMessage());
}
System.err.println(e.getMessage());
}finally{
HibernateUtil.closeSession();
}
}
@SuppressWarnings("unchecked")
public <T> List<T> selectAll(String hql) {
List<T> items = null;
Transaction tc = null;
try{
Session session = HibernateUtil.getSession();
tc = session.beginTransaction();
Query query = session.createQuery(hql);
items = query.list();
tc.commit();
}catch(HibernateException e){
try{
if(tc != null){
tc.rollback();
items = null;
}
}catch(Exception ex){
System.err.println(ex.getMessage());
}
System.err.println(e.getMessage());
}finally{
//HibernateUtil.closeSession();
}
return items;
}
}
HibernateUtil.java:
package wintys.hibernate.manytomany;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
/**
* Hibernate Session管理
* @author Winty
*/
public class HibernateUtil {
private static SessionFactory factory = null;
private static ThreadLocal<Session> threadLocal;
static {
try{
factory = new Configuration()
.configure()
.buildSessionFactory();
}catch(HibernateException e){
System.err.println(e.getMessage());
}
threadLocal = new ThreadLocal<Session>();
}
private HibernateUtil(){
}
public static Session getSession()throws HibernateException{
Session session = threadLocal.get();
if(session == null){
session = factory.openSession();
threadLocal.set(session);
}
return session;
}
public static void closeSession()throws HibernateException{
Session session = threadLocal.get();
if(session != null){
session.close();
}
threadLocal.set(null);
}
}
course.jsp:查询Course及其学生列表
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%@ page import="wintys.hibernate.manytomany.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'index.jsp' starting page</title>
</head>
<body>
<%
List<Course> courses = null;
DAO dao = new DAOBean();
//dao.insert();
courses = dao.selectAll("from Course");
Iterator<Course> it = courses.iterator();
while(it.hasNext()){
Course course = it.next();
int id = course.getId();
String name = course.getName();
out.println("id:" + id + "<br />");
out.println("name:" + name + "<br />");
out.println("students:<br />");
Set<Student> students = course.getStudents();
Iterator<Student> itc = students.iterator();
while(itc.hasNext()){
Student student = itc.next();
int studentId = student.getId();
String studentName = student.getName();
out.println(" id:" + studentId + "<br />");
out.println(" name:" + studentName + "<br />");
}
out.println("<hr/>");
}
%>
</body>
</html>
5、运行结果
Web页面显示:
id:1
name:Course 1
students:
id:1
name:Student 1
--------------------------------------------------------------------------------
id:2
name:Course 2
students:
id:2
name:Student 2
id:1
name:Student 1
--------------------------------------------------------------------------------
id:3
name:Course 3
students:
id:2
name:Student 2
--------------------------------------------------------------------------------
[参考资料]:
Hibernate 多对多双向关联-熔岩 : http://lavasoft.blog.51cto.com/62575/39344
原创作品，转载请注明出处。
作者:Winty (wintys@gmail.com)
博客:http://www.blogjava.net/wintys
posted on 2009-06-19 22:50
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