继承关系中的第三种方式：利用<union-subclass>（补充）

继承关系中的第三种方式：利用<union-subclass>

 

代码：

 

映射文件（其他的代码和其他继承关系相同）

 

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">

 

<hibernate-mapping package="qau.edu.union">

 

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

   

       <id name="id" column="t_id">

          <generator class="hilo"/>

       </id>

      

     

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

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

      

       <!-- 配置继承关系 （利用union-subclass进行）-->

      

       <union-subclass name="Teacher" table="TEACHER">

          

           <property name="job"/>

          

       </union-subclass>

      

      

    </class>

   

</hibernate-mapping>

 

 

执行结果：

 

进行Save操作的结果：

 

 

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, t_id)

    values

        (?, ?, ?)

Hibernate:

    insert

    into

        TEACHER

        (t_name, t_date, job, t_id)

    values

        (?, ?, ?, ?)

 

 

 

 

只有两条记录，说明还是比较方便的。

 

获取对象的操作的执行结果：

 

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 t2_0_0_,

        person0_.t_date as t3_0_0_,

        person0_.job as job1_0_,

        person0_.clazz_ as clazz_0_

    from

        ( select

            t_id,

            t_name,

            t_date,

            null as job,

            0 as clazz_

        from

            t_person

        union

        select

            t_id,

            t_name,

            t_date,

            job,

            1 as clazz_

        from

            TEACHER

    ) person0_

where

    person0_.t_id=?

名字是：AAA

Hibernate:

    select

        teacher0_.t_id as t1_0_0_,

        teacher0_.t_name as t2_0_0_,

        teacher0_.t_date as t3_0_0_,

        teacher0_.job as job1_0_

    from

        TEACHER teacher0_

    where

        teacher0_.t_id=?

工作是：Teacher

 

 

 

通过这样的执行结果可以看出：在执行子类的查询的时候只是访问的是子类的表，但是进行父类的查询的时候却是进行的两张表的查询。这是比较麻烦的事情。

但是这是这种方式<union-subclass>的一种优势。