Table per class hierarchy
前兩種方式，都要進行多表操作，這樣帶來的性能的消耗量是相當可觀的，不利于高并發量的數據存取。
Table per class hierarchy提供了另外一中選擇。
實際開發中，通過冗余字段表達同類型數據是很多情況下的選擇。
建立一個數據表T_Item包含了所有商品可能用到的字段。另外，為了區分不同的商品，還需要引入一個用于區分的字段。
1.數據表如下圖：
2.數據表定義sql
use?sample;
DROP?TABLE?T_Item;
CREATE?TABLE?T_Item?(
???????id?INT?NOT?NULL?AUTO_INCREMENT
?????,?category?VARCHAR(10)
?????,?name?VARCHAR(50)
?????,?manufacturer?VARCHAR(50)
?????,?regioncode?VARCHAR(30)
?????,?pagecount?INT
?????,?PRIMARY?KEY?(id)
);
3.配置文件
TItem.hbm.xml:
注意，discriminator定義要緊跟在id定義之后。如果在property之后定義，會報錯誤。
(meta*,subselect?,cache?,synchronize*,comment?,tuplizer
*,(id|composite-id),discriminator?,natural-id?,(version|timestamp)?,(property|many-to-one|one-to-one|component|dynamic-component|properties|any|map|set|list|bag|idbag|array|primitive-array)*,((join*,subclass*)|joined-subclass*|union-subclass*),loader?,sql-insert?,sql-update?,sql-delete?,filter*,resultset*,(query|sql-query)*)
<?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>
????????
????????<discriminator?column="category"?type="string"></discriminator>
????????????????
????????<property?name="name"?column="name"/>
????????<property?name="manufacturer"?column="manufacturer"/>????????
????????
????????<subclass?name="TBook"?discriminator-value="1">
????????????<property?name="pageCount"?column="pagecount"></property>
????????</subclass>
????????
????????<subclass?name="TDVD"?discriminator-value="2">
????????????<property?name="regionCode"?column="regioncode"></property>
????????</subclass>????????
???????????????
????</class>
</hibernate-mapping>
4.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("byf");
????????????book1.setName("Java?beginner");
????????????book1.setPageCount(501);
????????????
????????????TBook?book2?=?new?TBook();
????????????book2.setManufacturer("yyy");
????????????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)?{
????????????//?TODO:?handle?exception
????????????e.printStackTrace();
????????????Assert.fail(e.getMessage());
????????????if(tran?!=?null)?{
????????????????try?{
????????????????????tran.rollback();
????????????????}?catch?(Exception?e1)?{
????????????????????//?TODO:?handle?exception
????????????????????e1.printStackTrace();
????????????????}
????????????}
????????}
????}
????
????public?void?testSelect(){
????????List?list?=?session.createQuery("?from?TBook").list();
????????
????????Iterator?it?=?list.iterator();
????????while?(it.hasNext())?{
????????????TBook?book?=?(TBook)it.next();
????????????System.out.println(book.getName());????????????
????????}
????????
????????list?=?session.createQuery("?from?TDVD").list();
????????it?=?list.iterator();
????????while?(it.hasNext())?{
????????????TDVD?dvd?=?(TDVD)it.next();
????????????System.out.println(dvd.getName());????????????
????????}????????
????}
}
4.查詢結果
posted on 2006-07-05 15:04
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