多对多投射

多对多映射

多对多映射表现为在两个表之外产生一个中间表,其主键为两个表的外键.

如下:

Person与Event为多对多关联.除了产生person,event表外,还会产生person_event表.

映射文件:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.lwf.hibernate.many2many"><class name="Event" table="EVENTS"><id name="id" column="Event_ID"><generator type="timestamp" column="Event_Date"/><set name="participants" table="Person_Event" inverse="true"><key column="Event_ID"/><many-to-many column="Person_id" ><id name="id" column="Person_ID"><generator table="Person_Event" ><key column="Person_id"/><many-to-many column="Event_ID" table="Person_Email_Addr" ><key column="Person_id"/><element type="string" column="Emai_Addr"/></set></class></hibernate-mapping>

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POJO

package com.lwf.hibernate.many2many;import java.util.HashSet;import java.util.Set;public class Person {private long id;private String name;private int age;private Set events = new HashSet();private Set emailAddress = new HashSet();public long getId() {return id;}public void setId(long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public Set getEvents() {return events;}public void setEvents(Set events) {this.events = events;}public Set getEmailAddress(){return emailAddress;}public void setEmailAddress(Set emailAddress){this.emailAddress = emailAddress;}}

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package com.lwf.hibernate.many2many;import java.util.Date;import java.util.HashSet;import java.util.Set;public class Event {private long id;private String title;private Date date;private Set participants = new HashSet();public Event(){}public long getId() {return id;}public void setId(long id) {this.id = id;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}public Date getDate() {return date;}public void setDate(Date date) {this.date = date;}public Set getParticipants() {return participants;}public void setParticipants(Set participants) {this.participants = participants;}}

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测试类:

package com.lwf.hibernate.many2many;import java.util.Date;import java.util.Iterator;import java.util.Set;import org.hibernate.Session;import com.lwf.hibernate.util.HibernateUtil;import com.lwf.hibernate.util.MapUtil;public class Many2ManyTest {public static void main(String[] args) {//addPerson();//addEvent();//addPersonToEvent(1L,1L);//addEmaiAddrToPerson(1L,"zhang@126.com");//save();load();}public static void load(){MapUtil map = new MapUtil();map.begin();Session session = map.getSession();Person aPerson = (Person)session.load(Person.class, 1L);System.out.println(aPerson.getName());Set events = aPerson.getEvents();for (Iterator iterator = events.iterator(); iterator.hasNext();) {Event event = (Event) iterator.next();System.out.println(event.getTitle());System.out.println(event.getDate());}map.commit();map.close();}public static void addEmaiAddrToPerson(Long personId,String emailAddr){Session session = HibernateUtil.getSession();session.beginTransaction();Person aPerson = (Person)session.load(Person.class, personId);aPerson.getEmailAddress().add(emailAddr);HibernateUtil.commit(session);}public static void addPersonToEvent(Long personId, Long eventId){Session session = HibernateUtil.getSession();session.beginTransaction();Person aPerson = (Person)session.load(Person.class, personId);Event anEvent = (Event)session.load(Event.class, eventId);aPerson.getEvents().add(anEvent);HibernateUtil.commit(session);}public static void addPerson(){Session session = HibernateUtil.getSession();session.beginTransaction();Person person = new Person();person.setName("li");person.setAge(16);session.save(person);HibernateUtil.commit(session);}public static void addEvent(){Session session = HibernateUtil.getSession();session.beginTransaction();Event event = new Event();event.setTitle("event_title2");event.setDate(new Date());session.save(event);HibernateUtil.commit(session);}public static void save(){MapUtil map = new MapUtil();map.begin();Person person = new Person();person.setName("person1");person.setAge(22);Event event = new Event();event.setTitle("title1");event.setDate(new Date());map.save(event);Event event1 = new Event();event1.setTitle("title2");event1.setDate(new Date());map.save(event1);person.getEvents().add(event);person.getEvents().add(event1);map.save(person);map.commit();map.close();}}

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