Table per subclass:
父類TItem單獨映射到一張主表，為子類TBook、TDVD分別單獨設立一張子表，子表中只包含子類所擴展的屬性。同時，子表通過關系型數據庫的外鍵相關聯，如下圖所示：
數據關系圖如下：
1.表定義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.測試代碼。
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("電子工業");
????????????book1.setName("Java?beginner");
????????????book1.setPageCount(501);
????????????
????????????TBook?book2?=?new?TBook();
????????????book2.setManufacturer("機械工業");
????????????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中輸入 From TItem，在Hibernate Dynamic Query Translator中觀察到如下的SQL語句：
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
posted on 2006-07-05 15:02
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