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hibernate中的继承关系

 

  1. 1.       hibernate中的继承关系

 

代码;

 

<1>POJO类:(Person类)

 

package qau.edu;

 

import java.util.Date;

 

public class Person {

 

//  成员变量;

   

    private int id ;

    private String name ;

    private Date date ;

   

//  相应的getter和setter方法;

   

    public int getId() {

       return id;

    }

    public void setId(int id) {

       this.id = id;

    }

    public String getName() {

       return name;

    }

    public void setName(String name) {

       this.name = name;

    }

    public Date getDate() {

       return date;

    }

    public void setDate(Date date) {

       this.date = date;

    }

   

 

   

   

}

 

 

 

Teacher类)

 

package qau.edu;

 

public class Teacher extends Person {

 

//  成员变量;

   

    private String job ;

   

   

//  相应的getter和setter 方法;

   

    public void setJob(String job){

      

       this.job = job ;

    }

    public String getJob(){

      

       return job ;

    }

}

 

 

 

<2>、关系映射文件;

 

Person

 

<?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="qau.edu">

 

    <class name="Person" table="t_person" discriminator-value=http://www.mamicode.com/"Person">

   

       <id name="id" column="t_id">

          <generator class="native"/>

       </id>

      

       <!-- 配置辨别项 -->

      

       <discriminator column="TYPE"/>

      

       <property name="name" column="t_name"/>

       <property name="date" column="t_date"/>

      

       <!-- 配置继承关系 -->

      

       <subclass name="Teacher" discriminator-value=http://www.mamicode.com/"Teacher">

          <property name="job" column="T_job"/>

       </subclass>

      

      

    </class>

   

</hibernate-mapping>

 

 

 

<3>、测试类;(进行相关的保存和查询的操作)

 

 

package qau.edu;

 

import java.util.Date;

 

import org.hibernate.Session;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

 

public class RenTest {

 

        

         private Session session ;

         private Transaction tr ;

        

        

         @Before

         public void init(){

                  

//               打开Session ;

                  

                   session = new Configuration().configure().buildSessionFactory().openSession();

                  

//               开启事务;

                  

                   tr = session.beginTransaction();

                  

                  

         }

        

        

         @After

         public void destroy(){

                  

//               提交事务;

                  

                   tr.commit();

                  

//               关闭会话;

                  

                   session.close();

         }

        

        

        

//     进行保存操作;

        

         @Test

         public void testSave() {

                  

//               实例化对象;

                  

                   Person per = new Person();

                  

//               设置属性值;

                  

                   per.setName("AAA");

                   per.setDate(new Date());

                  

                  

//               实例化Teacher对象;

                  

                   Teacher teacher = new Teacher();

                  

//               设置属性值;

                  

                   teacher.setName("BB");

                   teacher.setDate(new Date());

                   teacher.setJob("Teacher");

                  

//               保存对象;

                  

                   session.save(per);

                   session.save(teacher);

                  

 

                  

         }

        

        

//     进行查询操作;

        

         @Test

         public void testGet(){

                  

//               获取对象;

                  

                   Person  per = (Person)session.get(Person.class, 1);

                  

//               输出;

                  

                   System.out.println("名字是:" + per.getName());

                  

//               获取teacher对象;

                  

                   Teacher ter = (Teacher)session.get(Teacher.class, 2);

                  

//               输出:

                  

                   System.out.println("工作是:" + ter.getJob());

         }

 

}

 

 

 

执行结果:

 

 

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

Hibernate:

    select

        person0_.t_id as t1_0_0_,

        person0_.t_name as t3_0_0_,

        person0_.t_date as t4_0_0_,

        person0_.T_job as T5_0_0_,

        person0_.TYPE as TYPE0_0_

    from

        t_person person0_

    where

        person0_.t_id=?

名字是:AAA

Hibernate:

    select

        teacher0_.t_id as t1_0_0_,

        teacher0_.t_name as t3_0_0_,

        teacher0_.t_date as t4_0_0_,

        teacher0_.T_job as T5_0_0_

    from

        t_person teacher0_

    where

        teacher0_.t_id=?

        and teacher0_.TYPE=‘Teacher‘

工作是:Teacher

Hibernate:

    insert

    into

        t_person

        (t_name, t_date, TYPE)

    values

        (?, ?, ‘Person‘)

Hibernate:

    insert

    into

        t_person

        (t_name, t_date, T_job, TYPE)

    values

        (?, ?, ?, ‘Teacher‘)

 

 

 

 

另一种方法:

 

 

代码:

 

映射文件:

 

 

<?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="qau.edu">

 

    <class name="Person" table="t_person">

   

       <id name="id" column="t_id">

          <generator class="native"/>

       </id>

      

     

       <property name="name" column="t_name"/>

       <property name="date" column="t_date"/>

      

       <!-- 配置继承关系 -->

      

       <joined-subclass name="Teacher">

      

          <key column="T_Id"/>

          <property name="job"/>

       </joined-subclass>

      

      

    </class>

   

</hibernate-mapping>

 

 

其他的代码相同:

 

执行结果:

 

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

Hibernate:

    insert

    into

        t_person

        (t_name, t_date)

    values

        (?, ?)

Hibernate:

    insert

    into

        t_person

        (t_name, t_date)

    values

        (?, ?)

Hibernate:

    insert

    into

        Teacher

        (job, T_Id)

    values

        (?, ?)

 

 

 

通过上面知道:

 

 

第一种方式也就是<subclass>时候进行插入的时候是在一张表中进行的,但是在第二种的时候却是:

进行插入父类数据的时候是只在父表中进行的,但是当进行子类数据的插入时候却是先进行的父表的插入,然乎再进行的子类表的插入,因为第一种方式只是生成了一张表,第二种则是生成了两个表。

 

 

 

hibernate中的继承关系