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()
>0true);
            Assert.assertEquals(book2.getId().intValue()
>0true);
            Assert.assertEquals(dvd1.getId().intValue()
>0true);
            Assert.assertEquals(dvd2.getId().intValue()
>0true);
        } 
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
posted on 2006-07-05 15:02 knowhow 阅读(251) 评论(0)  编辑  收藏 所属分类: ORM:Hibernate及其他

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