Hibernate（十）继承结构映射

Hibernate中继承结构映射有三种实现方式：

使用一张表（映射文件名与超类相同）

每个类一张表（抽象类也对应表。每个表中只有当前类中的属性）

每个具体类对应一张表（抽象类不对应表。每个表中都有全部的信息，包括继承过来的信息）

这里以论坛帖子和回复为例。
整个继承结构使用一张表（每个列不可以有not null约束）

超类

package test.hibernate.hbmExtends;

import java.util.Date;

public class Article {

private Integer id;
private String title;
private String content;
private Date postTime;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public Date getPostTime() {
return postTime;
}
public void setPostTime(Date postTime) {
this.postTime = postTime;
}

}

package test.hibernate.hbmExtends;

public class Topic extends Article{

private int type;//精华、置顶

public int getType() {
return type;
}

public void setType(int type) {
this.type = type;
}

}

package test.hibernate.hbmExtends;

public class Reply extends Article{

private int floor;

public int getFloor() {
return floor;
}

public void setFloor(int floor) {
this.floor = floor;
}

}

这里只有一个配置文件Article.hbm.xml

<?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="test.hibernate.hbmExtends">
<!--
discriminator-value属性：用于鉴别是哪个类的一个值，表示这
个值就是这个类。 如果不写，默认为类的全限定名。
-->
<class name="Article" table="article" discriminator-value="Article">
<id name="id" type="integer" column="id">
<generator class="native" />
</id>

<discriminator type="string" column="class_"></discriminator>

<property name="title" />
<property name="content" />
<property name="postTime" type="timestamp" />

<subclass name="Topic" discriminator-value="Topic">
<property name="type"></property>
</subclass>

<subclass name="Reply" discriminator-value="Reply">
<property name="floor"></property>
</subclass>

</class>
</hibernate-mapping>

package test.hibernate.hbmExtends;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

public class App {

private static SessionFactory sessionFactory = new Configuration()//
.configure()//
.addClass(Article.class)// 添加Hibernate实体类（加载对应的映射文件）
.buildSessionFactory();

@Test
public void testSave() throws Exception {
Session session = sessionFactory.openSession();
session.beginTransaction();
// --------------------------------------------

// 构建对象
Article article = new Article();
article.setTitle("这是一篇文章");

Topic topic = new Topic();
topic.setTitle("这是一张帖子");

Reply reply = new Reply();
reply.setTitle("这是一张回复");

// 保存
session.save(article);
session.save(topic);
session.save(reply);

// --------------------------------------------
session.getTransaction().commit();
session.close();
}

@Test
public void testGet() throws Exception {
Session session = sessionFactory.openSession();
session.beginTransaction();

// 获取数据
// Article article=(Article) session.get(Article.class, 1);
// Topic topic=(Topic) session.get(Topic.class, 2);
// Reply reply=(Reply) session.get(Reply.class, 3);

Article article = (Article) session.get(Article.class, 1);
Article topic = (Article) session.get(Article.class, 2);
Article reply = (Article) session.get(Article.class, 3);

System.out.println(article);
System.out.println(topic);
System.out.println(reply);

session.getTransaction().commit();
session.close();
}
}

表结构
article



每个类一张表
Article.hbm.xml

<?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="test.hibernate.hbmExtends2">
<!-- 采用每个类一张表的方式，抽象类也对应表 -->
<class name="Article" table="article2">
<id name="id" type="integer" column="id">
<generator class="native" />
</id>

<property name="title" />
<property name="content" />
<property name="postTime" type="timestamp" />
<!-- 定义子类Topic -->
<joined-subclass name="Topic" table="topic2">
<key column="id"></key>
<property name="type"></property>
</joined-subclass>
<!-- 定义子类Reply -->
<joined-subclass name="Reply" table="reply2">
<key column="id"></key>
<property name="floor"></property>
</joined-subclass>

</class>
</hibernate-mapping>

package test.hibernate.hbmExtends2;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

public class App {

private static SessionFactory sessionFactory = new Configuration()//
.configure()//
.addClass(Article.class)// 添加Hibernate实体类（加载对应的映射文件）
.buildSessionFactory();

@Test
public void testSave() throws Exception {
Session session = sessionFactory.openSession();
session.beginTransaction();
// --------------------------------------------

// 构建对象
Article article = new Article();
article.setTitle("这是一篇文章");

Topic topic = new Topic();
topic.setTitle("这是一张帖子");

Reply reply = new Reply();
reply.setTitle("这是一张回复");

// 保存
session.save(article);
session.save(topic);
session.save(reply);

// --------------------------------------------
session.getTransaction().commit();
session.close();
}

@Test
public void testGet() throws Exception {
Session session = sessionFactory.openSession();
session.beginTransaction();

// 获取数据
// Article article=(Article) session.get(Article.class, 1);
// Topic topic=(Topic) session.get(Topic.class, 2);
// Reply reply=(Reply) session.get(Reply.class, 3);

Article article = (Article) session.get(Article.class, 1);
Article topic = (Article) session.get(Article.class, 2);
Article reply = (Article) session.get(Article.class, 3);

System.out.println(article);
System.out.println(topic);
System.out.println(reply);

session.getTransaction().commit();
session.close();
}
}

article2



reply2



topic2



每个具体类对应一张表

<?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="test.hibernate.hbmExtends3">
<!-- 采用每个具体类一张表的形式，抽象类不对应表。
abstract默认为false,设为true表示本类不对应表
（类可以不是abstract的）， 这时就会忽略table属性 -->
<class name="Article" abstract="false" table="article3">
<id name="id">
<!-- 这里native生成策略不能用 -->
<!-- 使用每个具体类一张表的方式时，主键生成策略不能是identity。因为在整个 继承结构中，主键值是不能重复的。 -->
<generator class="hilo">
<param name="table">hi_value</param>
<param name="column">next_value</param>
<param name="max_lo">5</param>
</generator>
</id>

<property name="title" />
<property name="content" />
<property name="postTime" type="timestamp" />
<!-- 子类Topic -->
<union-subclass name="Topic" table="topic3">
<property name="type"></property>
</union-subclass>
<!-- 子类Reply -->
<union-subclass name="Reply" table="reply3">
<property name="floor"></property>
</union-subclass>

</class>
</hibernate-mapping>

article3





reply3



topic3