保存对象、关系映射

首先是Event类，

 

public class Event {
	 private int id;

	    private String title;
	    private Date date;
	    private Set participants = new HashSet();
	    

	    public Event() {}


	    public Date getDate() {
	        return date;
	    }

	    public void setDate(Date date) {
	        this.date = date;
	    }

	    public String getTitle() {
	        return title;
	    }

	    public void setTitle(String title) {
	        this.title = title;
	    }


		public int getId() {
			return id;
		}


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


		public Set getParticipants() {
			return participants;
		}


		public void setParticipants(Set participants) {
			this.participants = participants;
		}

}

其对应的hibernate映射文件为：Event.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cjq.hibernate.tutorial.domain">
	<class name="Event" table="HI_EVENTS">
        <id name="id" column="EVENT_ID">
            <generator class="native"/>
        </id>
        <property name="date" type="timestamp" column="EVENT_DATE"/>
        <property name="title"/>
        <set name="participants" table="HI_PERSON_EVENT">
        	<key column="EVENT_ID"/>
        	<many-to-many column="PERSON_ID" class="PERSON"/>
        </set>
    </class>
</hibernate-mapping>

事件与人有多对多的关联。

Person类为：

public class Person {
	 	private int id;
	    private int age;
	    private String firstname;
	    private String lastname;
	    private Set events = new HashSet(); 
	    
	    private Set emailAddresses = new HashSet();
		public int getAge() {
			return age;
		}
		public void setAge(int age) {
			this.age = age;
		}
		public String getFirstname() {
			return firstname;
		}
		public void setFirstname(String firstname) {
			this.firstname = firstname;
		}
		public String getLastname() {
			return lastname;
		}
		public void setLastname(String lastname) {
			this.lastname = lastname;
		}
		public Set getEvents() {
			return events;
		}
		public void setEvents(Set events) {
			this.events = events;
		}
		public void setId(int id) {
			this.id = id;
		}
		public int getId() {
			return id;
		}
		public Set getEmailAddresses() {
			return emailAddresses;
		}
		public void setEmailAddresses(Set emailAddresses) {
			this.emailAddresses = emailAddresses;
		}
		
		@SuppressWarnings("unchecked")
		public void addToEvnet(Event event){
			this.getEvents().add(event);
			event.getParticipants().add(this);
		}
		
		public void removeFromEvent(Event event){
			this.getEvents().remove(event);
			event.getParticipants().remove(this);
		}

}

其对应的hibernate配置文件Person.hbm.xml为：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cjq.hibernate.tutorial.domain">
	<class name="Person" table="HI_PERSON">
        <id name="id" column="PERSON_ID">
            <generator class="native"/>
        </id>
        <property name="age"/>
        <property name="firstname"/>
        <property name="lastname"/>
        <set name="events" table="HI_EVENT">
        	<key column="PERSON_ID"/>
        	<many-to-many column="EVENT_ID" class="Event"/>
        </set>
        <set name="emailAddresses" table="HI_PERSON_EMAIL_ADDR">
        	<key column="PERSON_ID"/>
        	<element type="string" column="EMAIL_ADDR"/>
        </set>
    </class>
</hibernate-mapping>

这里，也体现出人与事件多对多的关系，同时，还加入的人的email地址的元素，用集合表示，说明有一个可能有多个email。

下面就要对定义的两个实体进行操作。

首先，创建一个Event实例，并将具体数据存入数据库：

private void createAndStoreEvent(String title, Date theDate){
		Session session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		
		Event event = new Event();
		event.setDate(theDate);
		event.setTitle(title);
		session.save(event);
		
		
		session.getTransaction().commit();
		
		//HibernateUtil.getSessionFactory().close();
		
	}

同样，对Person实例的操作：

private void createPerson(int age,String firstname,String lastname){
		Session session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		
		Person person = new Person();
		person.setAge(age);
		person.setFirstname(firstname);
		person.setLastname(lastname);
		session.save(person);
		
		session.getTransaction().commit();
	}

上面两个方法只是简单的保存数据，并未建立关联。

为事件添加关联：

private void addPersonToEvent(int personId,int eventId){
		Session session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		
		Person person = (Person)session.load(Person.class, personId);
		Event event = (Event)session.load(Event.class, eventId);
		person.getEvents().add(event);
		
		session.getTransaction().commit();
		
	}

为人添加关联，针对于人与email的关系：

private void addEmailToPerson(int personId,String emailAddress){
		Session session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		
		Person person = (Person)session.load(Person.class, personId);
		person.getEmailAddresses().add(emailAddress);
		
		session.getTransaction().commit();
	}

在为事件添加关联，也可以使用两个不同的事务进行操作：

private void addPersonToEvent2(int personId,int eventId){
		Session session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		
		Person person = (Person)session.createQuery("select p from Person p left join fetch p.events where p.id=:pid").setParameter("pid", personId).uniqueResult();
		Event event = (Event)session.load(Event.class, eventId);
		session.getTransaction().commit();
		//End of first unit of work;
		person.getEvents().add(event);
		
		//begin second unit of work;
		Session session2 = HibernateUtil.getSessionFactory().getCurrentSession();
		session2.beginTransaction();
		session2.update(person);
		session2.getTransaction().commit();
		System.out.println("finish");
		
	}

补充说明一下：

获取实体列表操作如下：

private List getEventList(String title, Date theDate){
		Session session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		
		
		List list = session.createQuery("from Event").list();
		
		session.getTransaction().commit();
		
		return list;
	}

说明："from Event"中Event为实体的类名，而不数据库的表名。