14 继承(一)(整个继承树映射到一张表)

 

人类(Person)  , 男人(Men)继承"人"类, 女人(Women)继承"人"类,  UML如下:

 

 

映射到如下的t_person表中, 有以下6个字段:

1 int  id                             //主键

2 varchar  name                 //父类中的姓名

3 int  age                          //父类中的年龄      

4 int/varchar   type             //区分"人","男人","女人"  的专用字段, 默认类型是varchar, 也可以指定为int类型.  叫鉴别器字段

                                                           //Person类:type值设为0, Men类:type值设为1, Women类:type值设为2

 

5 varchar   a                      //"男人"类专有属性   

6 varchar   b                      //"女人"类专有属性    

 

Person, Men, Women 三个类这里就不显示了,但简单, 想看了附件中有源码

 

Person.hbm.xml 如下:

<?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="extends_test.extends_1" auto-import="false"><class name="Person" table="t_person" discriminator-value="0"><!-- "鉴别值"为0 --><!-- 父类的属性 --><id name="id"><generator class="native"/></id><!-- 重点:鉴别器 --><!-- 指定type字段,做区分父子具体类型用 ,各类还要指定"鉴别值": discriminator-value="1"--><discriminator column="type" type="int"/><!-- 父类的属性 --><property name="name"/><!-- 父类的属性 --><property name="age"/><!-- Mem子类的映射 --><subclass name="Men" discriminator-value="1"><!-- "鉴别值"为1 --><!-- Men类专有的属性a --><property name="a"/></subclass><!-- Women子类的映射 --><subclass name="Women" discriminator-value="2"><!-- "鉴别值"为2 --><!-- Women类专有的属性b --><property name="b"/></subclass></class></hibernate-mapping>

 

保存与查询操作:

package extends_test.extends_1;import org.hibernate.Session;import org.hibernate.Transaction;import dao.HibernateUtil;/** * 继承关系的映射(方法一) *  * 总个继承树映射到一张表 *  */public class Test{/** * @param args */public static void main(final String[] args){//add();query();}/** * 查询测试 */public static void query(){Session session = null;try{session = HibernateUtil.getSeesion();final Person p = (Person) session.get(Person.class, 2); //ID为2的记录是  Men类型System.out.println(p.getClass());//get()第一个参数用了 Person.class//能识别出是class extends_test.extends_1.Men类型}finally{if (session != null){session.close();}}}/** * 添加测试 */public static void add(){final Person p1 = new Person();p1.setName("我是Person类");final Men m1 = new Men();m1.setName("我是男人类");m1.setA("a");final Women w1 = new Women();w1.setName("我是女人类");w1.setB("b");Session session = null;try{session = HibernateUtil.getSeesion();final Transaction tx = session.beginTransaction();session.save(p1);session.save(m1);session.save(w1);tx.commit();//SQL如下 //Hibernate: insert into t_person (name, age, type) values (?, ?, 0)//Hibernate: insert into t_person (name, age, a, type) values (?, ?, ?, 1)//Hibernate: insert into t_person (name, age, b, type) values (?, ?, ?, 2)}finally{if (session != null){session.close();}}}}