两种针对继承的HBM文件编写方法

首先，有三个实体对象User，Student, Teacher

其中三者共同的属性是name,password,fullname,均定义在User中，Student和Teacher继承User

如果要在hibernate配置文件中定义上面的关系，有两种方法

（1）使用<union-subclass>          使用这种方式，三个表的字段名称必须完全相同（name,password,fullname）

< class  table ="userinfo"  name ="cm.hxex.exam.model.User" >      < id  name ="id"  column ="ID" >        < generator  class ="uuid.hex" />      </ id >      < property  name ="name"  column ="NAME" />      < property  name ="password"  column ="PASSWORD" />      < property  name ="fullname"  column ="FULLNAME" />      < union-subclass  table ="teacher"  name ="cn.hxex.exam.mode.Teacher" >          < many-to-one  column ="class_id"  cascade ="save-update"  name ="classes" />      </ union-subclass >       < union-subclass  table ="student"  name ="cn.hxex.exam.mode.Student" >         < set  cascade ="all"  lazy ="true"  table ="TEACHER_CLASS"  name ="classes" >           < key  column ="TEACHER_ID" />           < many-to-many  class ="cn.hxex.exam.model.Classes"  column ="CLASS_ID" />         </ set >       </ union-subclass > </ class >

 （2）使用单独的<class>

           可以解决字段名不一样的问题，但在每个子类中都要进行相应的属性定义，造成配置重复

  < class  table ="USERINFO"  name ="cn.hxex.exam.model.User" >      < id  name ="id"  column ="ID" >        < generator  class ="uuid.hex" />      </ id >      < property  name ="name"  column ="NAME" />      < property  name ="password"  column ="PASSWORD" />      < property  name ="fullname"  column ="FULLNAME" />    </ class >      < class  table ="STUDENT"  name ="cn.hxex.exam.model.Student" >      < id  name ="id"  column ="ID" >        < generator  class ="uuid.hex" />      </ id >      < many-to-one  column ="CLASS_ID"  cascade ="save-update"  name ="classes" />      < property  name ="name"  column ="NAME" />      < property  name ="password"  column ="PASSWORD" />      < property  name ="fullname"  column ="FULLNAME" />    </ class >      < class  table ="TEACHER"  name ="cn.hxex.exam.model.Teacher" >      < id  name ="id"  column ="ID" >        < generator  class ="uuid.hex" />      </ id >      < set  inverse ="true"  name ="papers" >        < key  column ="TEACHER_ID" />        < one-to-many  class ="cn.hxex.exam.model.TestPaper" />      </ set >      < set  cascade ="all"  lazy ="true"  table ="TEACHER_CLASS"  name ="classes" >        < key  column ="TEACHER_ID" />        < many-to-many  class ="cn.hxex.exam.model.Classes"  column ="CLASS_ID" />      </ set >      < property  name ="name"  column ="NAME" />      < property  name ="password"  column ="PASSWORD" />      < property  name ="fullname"  column ="FULLNAME" />    </ class >