hibernate <one-to-one>中的property-ref属性。 
person映射文件: 
<hibernate-mapping package="hibernatetest"> 
  <class name="Person" table="person"> 
    <id name="id" column="id"> 
      <generator class="native"></generator> 
    </id> 
   <property name="name" column="name"></property> 
<one-to-one name="idcard1" property-ref="person" ></one-to-one> 
  </class> 
</hibernate-mapping> IdCard映射文件: <hibernate-mapping package="hibernatetest"> 
  <class name="IdCard1" table="idcard1"> 
    <id name="id" column="id"> 
      <generator class="native"> 
      </generator> 
    </id> 
   <property name="uselife" column="uselife"></property> 
<many-to-one name="person" column="person_id" unique="true"></many-to-one> 
  </class> 
</hibernate-mapping> 我想知道在查找person的时候,hibernate是怎么到idcard1表中去查找相应person的???? 
property-ref=“”后面是引用吗?? 
property-ref这个属性不写好像也可以做查询,这个属性在这里是什么左右???