Hibernate入门07_继承映射02_joined方式

一、hibernate继承映射之joined方式

joined方式：子类从父类继承的字段存放在父类的表里，子类自己独有的字段存在自己的表里

二、还是以Student继承Person为例

三、代码

public class Person {private Integer id;private String name;private String age;//get/set...
}public class Student extends Person {private String school;//get/set...
}

Person.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">
<!-- Generated 2017-3-27 22:49:29 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="com.hibernate.n2n"><class name="Person" table="PERSONS"><id name="id" type="java.lang.Integer"><column name="ID" /><generator class="native" /></id><property name="name" type="java.lang.String"><column name="NAME" /></property><property name="age" type="java.lang.String"><column name="AGE" /></property><joined-subclass name="Student" table="STUDENTS"><key column="STUDENT_ID"></key><property name="school" type="string" column="SCHOOL"></property></joined-subclass></class>
</hibernate-mapping>

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration><session-factory><!-- 配置链接数据库的基本信息 --><property name="connection.username">root</property><property name="connection.password">root</property><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="connection.url">jdbc:mysql://localhost:3306/hibernate01</property><!-- hibernate的基本信息 --><!-- hibernate使用的数据库方言 --><property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property><!-- 执行操作时是否在控制台打印sql语句 --><property name="show_sql">true</property><!-- 是否对sql进行格式化 --><property name="format_sql">true</property><!-- 指定自动生成数据表的策略 --><property name="hbm2ddl.auto">update</property><!-- 设置hibernate的隔离级别 --><property name="connection.isolation">2</property><!-- 删除对象后，设置其OID为null --><property name="use_identifier_rollback">true</property><!-- 配置C3P0数据源 --><property name="c3p0.max_size">100</property><property name="c3p0.min_size">5</property><property name="c3p0.acquire_increment">2</property><property name="c3p0.idle_test_period">2000</property><property name="c3p0.timeout">2000</property><property name="c3p0.max_statements">10</property><!-- 设置JDBC的statement读取数据库的时候每次从数据库中读取记录条数，这个值100合适，太大会损耗内存，小了速度慢 --><property name="jdbc.fetch_size">100</property><!-- 设置数据库进行批量删除，更新，插入的时候批次的大小，30比较合适 --><property name="jdbc.batch_size">30</property><!-- 指定关联的hbm.xml文件 --><mapping resource="com/hibernate/n2n/Person.hbm.xml"/>      </session-factory>
</hibernate-configuration>

测试代码，Test

package com.hibernate.n2n;import static org.junit.Assert.*;import java.util.List;
import java.util.Set;import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;public class HibernateTest {private SessionFactory sessionFactory;private Session session;private Transaction transaction;/**** 插入性能稍弱*/@Testpublic void testSave(){Person person = new Person();person.setAge("22");person.setName("AA");session.save(person);Student student = new Student();student.setSchool("BB");student.setAge("18");student.setName("CC");session.save(student);}/**** 查询性能也稍弱* 没有冗余的字段*/@Testpublic void testQuery(){//查询父类数据，只需查询一张表List<Person> persons = session.createQuery("FROM Person").list();System.out.println(persons.size());//查询父类数据，也只需查询一张表List<Student> students = session.createQuery("FROM Student").list();System.out.println(students.size());}@Beforepublic void init() {System.out.println("HibernateTest.init()");// 1.创建一个sessionFactory对象Configuration configuration = new Configuration().configure();ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()).buildServiceRegistry();sessionFactory = configuration.buildSessionFactory(serviceRegistry);// 2.创建一个session对象session = sessionFactory.openSession();// 3.开启事务transaction = session.beginTransaction();}@Afterpublic void destroy() {System.out.println("HibernateTest.destroy()");// 5.提交事务transaction.commit();// 6.关闭sessionsession.close();// 7.关闭SessionFactorysessionFactory.close();}}

四，运行结果