Hibernate实体层次设计(三)

Hibernate实体层次设计(三)

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