hibernate单向多对多

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{
    ......
}

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:
......

2、实体类:
Student.java:

package wintys.hibernate.manytomany;

import java.util.Set;

/**
* @version 2009-06-19
* @author Winty ([e-mail])
*
*/
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 ([e-mail])
*
*/
public class Course {
    private Integer id;
    private String name;
   
    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;
    }
}



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" />
    </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&amp;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 ([e-mail])
*
*/
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);
    }
}



index.jsp:查询Student及其课程列表

<%@ 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<Student> students = null;
        DAO dao = new DAOBean();
        dao.insert();
        students = dao.selectAll("from Student");
           
        Iterator<Student> it = students.iterator();
        while(it.hasNext()){
            Student student = it.next();
            int id = student.getId();
            String name = student.getName();
            out.println("id:" + id + "<br />");
            out.println("name:" + name + "<br />");
            out.println("courses:<br />");
           
            Set<Course> cards = student.getCourses();
            Iterator<Course> itc = cards.iterator();
            while(itc.hasNext()){
                Course course = itc.next();
                int courseId = course.getId();
                String courseName = course.getName();
                out.println("&nbsp;&nbsp;&nbsp; id:" + courseId + "<br />");
                out.println("&nbsp;&nbsp;&nbsp; name:" + courseName + "<br />");
            }
            out.println("<hr/>");
        }
    %>

  </body>
</html>


5、运行结果
控制台显示:

......
Hibernate: insert into db.course (name, id) values (?, ?)
Hibernate: insert into db.course (name, id) values (?, ?)
Hibernate: insert into db.course (name, id) values (?, ?)
Hibernate: insert into db.student (name, id) values (?, ?)
Hibernate: insert into db.student (name, id) values (?, ?)
Hibernate: insert into student_course (studentid, courseid) values (?, ?)
Hibernate: insert into student_course (studentid, courseid) values (?, ?)
Hibernate: insert into student_course (studentid, courseid) values (?, ?)
Hibernate: insert into student_course (studentid, courseid) values (?, ?)
......


Web页面显示:
id:1
name:Student 1
courses:
    id:1
    name:Course 1
    id:2
    name:Course 2
--------------------------------------------------------------------------------
id:2
name:Student 2
courses:
    id:3
    name:Course 3
    id:2
    name:Course 2
--------------------------------------------------------------------------------

[参考资料]:
Hibernate 多对多单向关联-熔岩 : http://lavasoft.blog.51cto.com/62575/39324