hibernate的一对多时即时抓取策略

组织机构是一颗树型机构，一个父类对应多个子类。该对象的xml文件为

  

    

    
      
    

           
              
                  机构名称
              
          

        
              
                  职能描述
              
          

       

        
          
          
        

         
              
                  部门电话
              
          


          
              
                  排序号
              
           
  

形成机构树时，需要查询出所有节点，并且会根据节点来获取子节点。所以应该采用即时抓取。
方法一：设置lazy为false 也就是即时抓取
使用getHibernateTemplate().loadAll(Organization.class);能达到目的但会发出n+1条sql语句

  select
        this_.ID as ID0_0_,
        this_.ORGANIZATION_NAME as ORGANIZA2_0_0_,
        this_.DESCRIPTION as DESCRIPT3_0_0_,
        this_.PID as PID0_0_,
        this_.ORGANIZATION_TEL as ORGANIZA5_0_0_,
        this_.ORDER_NUM as ORDER6_0_0_ 
    from
        g_organization this_

Hibernate: 
    select
        childern0_.PID as PID1_,
        childern0_.ID as ID1_,
        childern0_.ID as ID0_0_,
        childern0_.ORGANIZATION_NAME as ORGANIZA2_0_0_,
        childern0_.DESCRIPTION as DESCRIPT3_0_0_,
        childern0_.PID as PID0_0_,
        childern0_.ORGANIZATION_TEL as ORGANIZA5_0_0_,
        childern0_.ORDER_NUM as ORDER6_0_0_ 
    from
        g_organization childern0_ 
    where
        childern0_.PID=? 
    order by
        childern0_.ORDER_NUM
。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。

第一条sql查询出所有记录，接下来会发出n条记录来获取所有相关的子记录。查询时间大概
20:26:18,105 INFO OrganizationBoTest:51 - *******发费时间******203

所以可以看出这种方式并不是最佳选择。
方法二： 设置抓取策略fetch="join" 并loadAll时只发送一条sql语句 fetch="join"只对load和get方法 还有就是条件查询会起作用，而对hsql的查询是不会有影响的

   select
        this_.ID as ID0_1_,
        this_.ORGANIZATION_NAME as ORGANIZA2_0_1_,
        this_.DESCRIPTION as DESCRIPT3_0_1_,
        this_.PID as PID0_1_,
        this_.ORGANIZATION_TEL as ORGANIZA5_0_1_,
        this_.ORDER_NUM as ORDER6_0_1_,
        childern2_.PID as PID3_,
        childern2_.ID as ID3_,
        childern2_.ID as ID0_0_,
        childern2_.ORGANIZATION_NAME as ORGANIZA2_0_0_,
        childern2_.DESCRIPTION as DESCRIPT3_0_0_,
        childern2_.PID as PID0_0_,
        childern2_.ORGANIZATION_TEL as ORGANIZA5_0_0_,
        childern2_.ORDER_NUM as ORDER6_0_0_ 
    from
        g_organization this_ 
    left outer join
        g_organization childern2_ 
            on this_.ID=childern2_.PID 
    order by
        childern2_.ORDER_NUM

发费时间大概为
20:28:01,450 INFO OrganizationBoTest:51 - ********发费时间*****178
但存在一个问题就是，对于许多其他查询应用可能不会操作子记录，也就没有立即抓取子节点的必要，而且这样会浪费内存。