hibernate学习之m:m映射

1、包结构:


2、源代码：
Course.java

package domain;

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

public class Course {
	private String id;
	private String cid;
	private String course;
	private Set<Student> students=new HashSet<Student>();

	public Course() {
	}

	public Course(String cid, String course) {
		this.cid = cid;
		this.course = course;
	}

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getCid() {
		return cid;
	}

	public void setCid(String cid) {
		this.cid = cid;
	}

	public String getCourse() {
		return course;
	}

	public void setCourse(String course) {
		this.course = course;
	}

	public Set<Student> getStudents() {
		return students;
	}

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

Student.java:

package domain;

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

public class Student {
	private String id;
	private String sid;
	private String name;
	private Set<Course> courses=new HashSet<Course>();
	public Student(){};
	public Student(String sid,String name){
		this.sid=sid;
		this.name=name;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getSid() {
		return sid;
	}
	public void setSid(String sid) {
		this.sid = sid;
	}
	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;
	}
	
}

HbnUtil.java:

package util;

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

public class HbnUtil {
	private static SessionFactory sessionFactory;
	private HbnUtil(){}
	public static synchronized SessionFactory getSessionFactory(){
		if(sessionFactory==null){
			sessionFactory=new Configuration().configure().buildSessionFactory();
		}
		return sessionFactory;
	}
}

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="dialect">org.hibernate.dialect.Oracle9Dialect</property>
        <property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:myorcl</property>
        <property name="connection.username">myorcl</property>
        <property name="connection.password">embed</property>
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="myeclipse.connection.profile">myorcl</property>
    	<!--<property name="hibernate.connection.release_mode">AFTER_TRANSACTION</property>
    	-->
    	<property name="show_sql">true</property>
    	<mapping resource="domain/Student.hbm.xml"/>
    	<mapping resource="domain/Course.hbm.xml"/>
    </session-factory>

</hibernate-configuration>

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 package="domain">
	<class name="Course" table="COURSE">
		<id name="id" column="id">
			<generator class="uuid"></generator>
		</id>
		<property name="cid" column="cid"></property>
		<property name="course" column="course"></property>
		<set name="students" table="SC" inverse="true">
			<key column="CFK"></key>
			<many-to-many class="Student" column="SFK"></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 package="domain">
	<class name="Student" table="STUDENT">
		<id name="id" column="ID">
			<generator class="uuid"></generator>
		</id>
		<property name="sid" column="SID"></property>
		<property name="name" column="NAME"></property>
		<set name="courses" table="SC" cascade="all">
			<key column="SFK"></key>
			<many-to-many class="Course" column="CFK"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

Test.java:

package test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;

import util.HbnUtil;
import domain.Course;
import domain.Student;


public class Test {
	public static void main(String[] args){
		SessionFactory sf=HbnUtil.getSessionFactory();
		Session session=sf.openSession();
		session.beginTransaction();
		
		Student s1=new Student("sid4","li");
		Course c1=new Course("cid4","C++");
		Student s2=new Student("sid5","li");
		Course c2=new Course("cid5","C++");
		
		s1.getCourses().add(c1);
		s1.getCourses().add(c2);
		c2.getStudents().add(s2);
		
		//session.save(s1);
		//session.save(c1);
		//session.save(c2);
		//session.save(s2);
		Object obj=session.get(Student.class, "4028e4282e091aa1012e091aa5420001");
		session.delete(obj);
		session.flush();
		
		session.getTransaction().commit();
		session.close();
		sf.close();
	}
}

以上代码使用中间表SC实现了多对多关系映射，但我还有一个疑问：就是如果中间表SC还想加入一个score（学生分数）字段，该如何处理呢？网上有人说将多对多映射拆成两个一对多映射。大家都是这么做的么？