hibernate小积累

最新推荐文章于 2022-01-02 20:35:32 发布

zjlolife

最新推荐文章于 2022-01-02 20:35:32 发布

阅读量508

点赞数

CC 4.0 BY-SA版权

分类专栏： hibernate

本文链接：https://blog.youkuaiyun.com/zjlolife/article/details/8846181

hibernate 专栏收录该内容

18 篇文章

订阅专栏

本文探讨了Hibernate中一对多关联映射的fetch与lazy属性的作用方式，以及不同设置下产生的SQL语句差异；同时介绍了Hibernate的一级缓存机制，并强调了级联操作与lazy属性之间的区别；最后提到了配置二级缓存时需要注意的顺序问题。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

①一对多的关联映射中set集合中fetch与lazy：

当fetch="join"的时候当加载teacher的时候会立即加载student,此时lazy="false",即延迟加载自动取消，即发出一条语句:

  select
        teacher0_.id as id0_1_,
        teacher0_.name as name0_1_,
        teacher0_.age as age0_1_,
        students1_.teacherid as teacherid0_3_,
        students1_.id as id3_,
        students1_.id as id1_0_,
        students1_.name as name1_0_,
        students1_.age as age1_0_ 
    from
        t_teacher teacher0_ 
    left outer join
        t_studnet students1_ 
            on teacher0_.id=students1_.teacherid 
    where
        teacher0_.id=?

当fetch="select"的时候当加载teacher的时候会立即加载student,此时lazy="true",

   select
        teacher0_.id as id0_0_,
        teacher0_.name as name0_0_,
        teacher0_.age as age0_0_ 
    from
        t_teacher teacher0_ 
    where
        teacher0_.id=?
select
        students0_.teacherid as teacherid0_1_,
        students0_.id as id1_,
        students0_.id as id1_0_,
        students0_.name as name1_0_,
        students0_.age as age1_0_ 
    from
        t_studnet students0_ 
    where
        students0_.teacherid=?

②hibernate缓存：
一级缓存：session级缓存是缓存实体对象的，不会缓存对象属性

③级联cascade与lazy，不要错误的认为各种加载会产生级联现象，级联操作仅仅存在各个关联对象中，1000个session对象在缓存中，只要有关系就会级联

④配置二级缓存的时候，要注意配置顺序，比如先是session-factory,再是property,mapping,class