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[原]Hibernate多對多(雙向)

[標題]:[原]Hibernate多對多(雙向)
[時間]:2009-6-19
[摘要]:Hibernate雙向多對多關聯。如:一個學生對應多門課程，一門課程也對應多名學生。
[關鍵字]:Hibernate，ORM，關聯，多對多，持久化，雙向，映射
[環境]:MyEclipse7，Hibernate3.2，MySQL5.1
[作者]:Winty (wintys@gmail.com) http://www.aygfsteel.com/wintys

[正文]:
 Hibernate單向多對多關聯。如:一個學生對應多門課程，一門課程也對應多名學生。本例單向關聯，只考慮學生到課程的一對多關聯。
1、概述
a.實體類
public class Student{
 ......
 private Set<Course> courses;
 ......
}

public class Course{
 ......
 private Set<Student> students;
 ......
}

b.數據庫表
 Student與Course各對應一張數據庫表，再建一張關聯表student_course (studentid,courseid)，保存多對多關聯。其中，student_course表的主鍵為studentid與courseid的聯合。

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、實體類:
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;
 //實現雙向"多對多"關聯
 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、數據庫表:
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)
);

-- 關聯表
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">


<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">


<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" />
 
 <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">


<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、使用測試:
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為兩個集合共有
 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中設置了cascade="all"，就不需要手動保存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:查詢Course及其學生列表

<%@ 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 + " ");
 out.println("name:" + name + " ");
 out.println("students: ");

 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 + " ");
 out.println("    name:" + studentName + " ");
 }
 out.println("<hr/>");
 }
 %>

</body>
</html>

5、運行結果

Web頁面顯示:
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
--------------------------------------------------------------------------------

[參考資料]:
Hibernate 多對多雙向關聯-熔巖 : http://lavasoft.blog.51cto.com/62575/39344

原創作品，轉載請注明出處。
作者:Winty (wintys@gmail.com)
博客:http://www.aygfsteel.com/wintys

posted on 2009-06-19 22:50 天堂露珠閱讀(398) 評論(0) 編輯收藏所屬分類: Hibernate

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