hibernate 联合主键查询 请教

对于 a 表 和  b 表 关联 ，a表中的order_id 为主键， b表中也有order_id但是 并没有 设为外键,
但在 hibernate 配置文件中 配置 成 一对多的形式a.hbm.xml
<set name="set" table="TB_ORDER_LOG"  inverse="true" lazy="false"> 
    <key column="ORDER_ID"/> 
    <one-to-many class="entity.TbOrderLog"/>
  </set> b.hbm.xml
<hibernate-mapping>
    <class name="entity.TbOrderLog" table="TB_ORDER_LOG" schema="PAY">
        <composite-id >
           
            <key-property name="orderAmount" type="java.lang.Double">
                <column name="ORDER_AMOUNT" precision="12" />
            </key-property>
            <key-property name="orderState" type="java.lang.Long">
                <column name="ORDER_STATE" precision="2" scale="0" />
            </key-property>
            <key-property name="operationTime" type="java.util.Date">
                <column name="OPERATION_TIME" length="11" />
            </key-property>
            <key-property name="operatorIp" type="java.lang.String">
                <column name="OPERATOR_IP" length="80" />
            </key-property>
            <key-property name="note" type="java.lang.String">
                <column name="NOTE" length="600" />
            </key-property>
        </composite-id>
        
        
       <property   name="orderId"   column="order_id"   type="string"   />       
       
       
            <many-to-one   name="order"   class="entity.TbOrder"   insert="false"   update="false"   cascade="save-update"   >   
                  <column   name="order_id"   />   
            </many-to-one>  
      
    </class>
</hibernate-mapping>想查出一个主键对应的 所有信息和  关联的信息，关联的信息 在 set中 ，
public List test()
{
String hql="from TbOrder  o  where o.orderId=?";
 
 TbOrder order=(TbOrder)getSession().createQuery(hql).setString(0, "2008102813JY00000545").uniqueResult();
 System.out.println(order.getOrderId());
 System.out.println(order.getPayAccountId());
 System.out.println(order.getSet().size());
 
 return null;
}请问 为什么 getSet().size()为0?