hibernate多对多的基础理解

转载自：http://www.blogjava.net/wujun/archive/2006/04/08/39956.html

1.建表

 create   table  student
(sid  varchar ( 32 )  not   null   primary   key ,
 sname  varchar ( 16 ),
 sage  varchar ( 16 ),
)

 create   table  course
(cid  varchar ( 32 )  not   null   primary   key ,
cname  varchar ( 16 )
)

 create   table  student_course_link
(sid  varchar ( 32 )  not   null ,
cid  varchar ( 32 )  not   null ,
 primary   key (sid,cid)
)

2.写VO
StudentVO
package com.test;
import java.util.Set;
public class Student
{
    private String sid;
    private String sname;
    private String sage;

    private Set course;
    public Student()
    {
    }
   //写上get set
Course vo
package com.test;

import java.util.Set;

public class Course
{
    private String cid;
    private String cname;
    private Set student;
   //写上get set

写配置文件
Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

    <class name="com.test.Student" table="student" >

        <id name="sid" type="string" unsaved-value="null" >
            <column name="sid" sql-type="char(32)" not-null="true"/>
            <generator class="uuid.hex"/>
        </id>

        <property name="sname">
            <column name="sname" sql-type="varchar(16)" not-null="true"/>
        </property>

        <property name="sage">
            <column name="sage" sql-type="varchar(16)" not-null="true"/>
        </property>

        <set name="course" table="student_course_link" cascade="all" outer-join="false">
            <key column="sid"/>
            <many-to-many class="com.test.Course" column="cid"/>
        </set>
   
    </class>

</hibernate-mapping>

Course.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

    <class name="com.test.Course" table="course" >

        <id name="cid" type="string" unsaved-value="null" >
            <column name="cid" sql-type="char(32)" not-null="true"/>
            <generator class="uuid.hex"/>
        </id>

        <property name="cname">
            <column name="cname" sql-type="varchar(16)" not-null="true"/>
        </property>

        <set name="student" table="student_course_link" lazy="false" cascade="all">
            <key column="cid"/>
            <many-to-many class="com.test.Student" column="sid"/>
        </set>
   
    </class>

</hibernate-mapping>

接着把下面的hibernate.properties文件拷到classes目录下。。这里用的是mysql
hibernate.query.substitutions true 1, false 0, yes 'Y', no 'N'
## MySQL
hibernate.dialect net.sf.hibernate.dialect.MySQLDialect
hibernate.connection.driver_class org.gjt.mm.mysql.Driver
hibernate.connection.url jdbc:mysql://localhost:3306/wjcms
hibernate.connection.username root
hibernate.connection.password wujun
hibernate.connection.pool_size 1
hibernate.proxool.pool_alias pool1
hibernate.show_sql true
hibernate.jdbc.batch_size 0
hibernate.max_fetch_depth 1
hibernate.cache.use_query_cache true 
写测试类了..
package com.test;

import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.cfg.Configuration;
import net.sf.hibernate.*;
import java.util.Set;
import java.util.HashSet;
import java.sql.*;
import java.util.List;
import java.util.Iterator;

public class TestManyToMany
{
    SessionFactory sf;
    Session session;
    public TestManyToMany()
    {
        try
        {
            Configuration cfg = new Configuration();
            sf = cfg.addClass(Student.class).addClass(Course.class).buildSessionFactory();
        }
        catch(HibernateException ex)
        {
            ex.printStackTrace();
        }
    }
    public void doCreate()
    {
        try
        {
            session = sf.openSession();

            Student student = new Student();
            student.setSname("小王");
            student.setSage("22");

            Set courseSet = new HashSet();
            Course course = null;
            for(int i=0;i<2;i++)
            {
                course = new Course();
                if(i==0)
                    course.setCname("c++");
                else if(i==1)
                    course.setCname("java");
                courseSet.add(course);
            }
            student.setCourse(courseSet);
            
            session.save(student);
            session.flush();
            session.connection().commit();

        }
        catch(HibernateException ex)
        {
            ex.printStackTrace();
        }
        catch(SQLException ex1)
        {
            ex1.printStackTrace();
        }
        finally
        {
                try{
                    session.close();
                }
                catch(HibernateException ex2){
                }
        }

    }
    public void doQuery()
    {
        try{
            session = sf.openSession();
            Query q = session.createQuery("select s from Student as s");
            List l = q.list();
            Student s = null;
            Course course = null;
            for(int i=0;i<l.size();i++)
            {
                s = (Student)l.get(i);
                System.out.println("姓名： "+s.getSname());
                System.out.println("年龄： "+s.getSage());
                System.out.println("所选的课程：");
                Iterator it = s.getCourse().iterator();
                while(it.hasNext())
                {
                    course = (Course)it.next();
                    System.out.println("课程名： "+course.getCname());
                }


            }

        }
        catch(HibernateException ex){
            ex.printStackTrace();
        }
        finally{
            try{
                session.close();
            }
            catch(HibernateException ex2){
            }
        }
    }
    public static void main(String[] args)
    {
        TestManyToMany t = new TestManyToMany();
        //t.doCreate();
        t.doQuery();
    }
}