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     */    @Test    public 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     */    @Test    public 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());    }    @Before    public 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();    }    @After    public void destroy() {        System.out.println("HibernateTest.destroy()");        // 5.提交事务        transaction.commit();        // 6.关闭session        session.close();        // 7.关闭SessionFactory        sessionFactory.close();    }}

四，运行结果