Table per subclass:
父类TItem单独映射到一张主表，为子类TBook、TDVD分别单独设立一张子表，子表中只包含子类所扩展的属性。同时，子表通过关系型数据库的外键相关联，如下图所示：
数据关系图如下：
1.表定义sql如下
use sample;
DROP TABLE T_DVD;
DROP TABLE T_Book;
DROP TABLE T_Item;
CREATE TABLE T_Item (
id INT NOT NULL AUTO_INCREMENT
, name VARCHAR(50)
, manufacturer VARCHAR(50)
, PRIMARY KEY (id)
);
CREATE TABLE T_Book (
id INT NOT NULL
, pagecount INT
, PRIMARY KEY (id)
, INDEX (id)
, CONSTRAINT FK_T_Book_1 FOREIGN KEY (id)
REFERENCES T_Item (id)
);
CREATE TABLE T_DVD (
id INT NOT NULL
, regioncode VARCHAR(30)
, PRIMARY KEY (id)
, INDEX (id)
, CONSTRAINT FK_T_DVD_1 FOREIGN KEY (id)
REFERENCES T_Item (id)
);
2.配置文件
TItem.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="cn.blogjava.start">
<class name="TItem" table="T_Item" catalog="sample">
<id name="id" column="id">
<generator class="native" />
</id>
<property name="name" column="name"/>
<property name="manufacturer" column="manufacturer"/>
<joined-subclass name="TDVD" table="T_DVD" catalog="sample">
<key column="id" />
<property name="regionCode" column="regioncode" />
</joined-subclass>
<joined-subclass name="TBook" table="T_Book" catalog="sample">
<key column="id" />
<property name="pageCount" column="pagecount" />
</joined-subclass>
</class>
</hibernate-mapping>
3.测试代码。
package cn.blogjava.start;
import java.util.Iterator;
import java.util.List;
import junit.framework.Assert;
import junit.framework.TestCase;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
public class HibernateTest extends TestCase {
Session session = null;
protected void setUp() {
try {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
session = sessionFactory.openSession();
} catch (HibernateException e) {
e.printStackTrace();
}
}
protected void tearDown() {
try {
session.close();
} catch (HibernateException e) {
e.printStackTrace();
}
}
public void testInsert() {
Transaction tran = null;
try {
tran = session.beginTransaction();
TBook book1 = new TBook();
book1.setManufacturer("电子工业");
book1.setName("Java beginner");
book1.setPageCount(501);
TBook book2 = new TBook();
book2.setManufacturer("机械工业");
book2.setName("Thinking in java");
book2.setPageCount(1201);
TDVD dvd1 = new TDVD();
dvd1.setManufacturer("columnibia");
dvd1.setName("Lord king");
dvd1.setRegionCode("5 area");
TDVD dvd2 = new TDVD();
dvd2.setManufacturer("sony");
dvd2.setName("Forrest gump");
dvd2.setRegionCode("3 area");
session.save(book1);
session.save(book2);
session.save(dvd1);
session.save(dvd2);
session.flush();
tran.commit();
Assert.assertEquals(book1.getId().intValue()>0, true);
Assert.assertEquals(book2.getId().intValue()>0, true);
Assert.assertEquals(dvd1.getId().intValue()>0, true);
Assert.assertEquals(dvd2.getId().intValue()>0, true);
} catch (HibernateException e) {
e.printStackTrace();
Assert.fail(e.getMessage());
if(tran != null) {
try {
tran.rollback();
} catch (Exception e1) {
e1.printStackTrace();
}
}
}
}
public void testSelect(){
List list = session.createQuery(" from TItem").list();
Iterator it = list.iterator();
while (it.hasNext()) {
TItem item = (TItem)it.next();
System.out.println(item.getName());
}
}
}
4.在HQL Scratchpad中输入 From TItem，在Hibernate Dynamic Query Translator中观察到如下的SQL语句：
select
titem0_.id as id16_,
titem0_.name as name16_,
titem0_.manufacturer as manufact3_16_,
titem0_1_.regioncode as regioncode17_,
titem0_2_.pagecount as pagecount18_,
case
when titem0_1_.id is not null then 1
when titem0_2_.id is not null then 2
when titem0_.id is not null then 0
end as clazz_
from
sample.T_Item titem0_
left outer join
sample.T_DVD titem0_1_
on titem0_.id=titem0_1_.id
left outer join
sample.T_Book titem0_2_
on titem0_.id=titem0_2_.id