hibernate 一对多表查询时fetchMode.join 生成left outer join 出来数据重复问题

hibernate 一对多表查询时fetchMode.join 生成left outer join 出来数据重复问题

 

@OneToMany(cascade = CascadeType.ALL, mappedBy = "vote", fetch = FetchType.lazy)   //fetch = FetchType.EAGER这样是否在session.find()时会马上关联查出子表呢?
 @JoinColumn(name="voteId")
 // Fetch策略定义
 @Fetch(FetchMode.join)

 

//如果设FetchMode.join会生成left outer join语句，这样出来的结果，就可能重复，一条主表记录对多条子表记录

遍历时会有与子表数里相等的记录list

 

//所以可以用session.find(from model a where a.x=?)

//同时把fetch = FetchType.eager会执行查询主表和子表

 

Hibernate:
    select
        this_.voteId as voteId23_0_,
        this_.arrangeMode as arrangeM2_23_0_,
        this_.audit as audit23_0_,
        this_.endTime as endTime23_0_,
        this_.isopened as isopened23_0_,
        this_.notice as notice23_0_,
        this_.popularity as popularity23_0_,
        this_.startTime as startTime23_0_,
        this_.status as status23_0_,
        this_.voteADNewName as voteADN10_23_0_,
        this_.voteADOldName as voteADO11_23_0_,
        this_.voteCity as voteCity23_0_,
        this_.voteCompany as voteCom13_23_0_,
        this_.voteInfoTitle as voteInf14_23_0_,
        this_.voteLimit as voteLimit23_0_,
        this_.voteMaker as voteMaker23_0_,
        this_.voteMode as voteMode23_0_,
        this_.voteName as voteName23_0_,
        this_.votePicNewName as votePic19_23_0_,
        this_.votePicOldName as votePic20_23_0_,
        this_.voteProvince as votePro21_23_0_,
        this_.voteRemark as voteRemark23_0_,
        this_.voteType as voteType23_0_,
        this_.voterInfo as voterInfo23_0_,
        this_.voterName as voterName23_0_
    from
        Vote this_
    where
        this_.voteMaker=?
Hibernate:
    select
        votecustom0_.voteId as voteId1_,
        votecustom0_.voteCustomApplyId as voteCust1_1_,
        votecustom0_.voteCustomApplyId as voteCust1_26_0_,
        votecustom0_.status as status26_0_,
        votecustom0_.voteId as voteId26_0_,
        votecustom0_.voteApplyName as voteAppl3_26_0_,
        votecustom0_.voteApplyTypeId as voteAppl4_26_0_
    from
        VoteCustomApply votecustom0_
    where
        votecustom0_.voteId in (
            select
                this_.voteId
            from
                Vote this_
            where
                this_.voteMaker=?
        )
    order by
        votecustom0_.voteCustomApplyId asc

 //----页面取子表的数据时还是没有子表数据

 

如果用session.find("FROM Vote v left join fetch v.voteCustomApplys WHERE v.voteMaker='"+voteMaker+"'")

 

去倒页面还没不能加载到子表

必须把fetch = FetchType.eager

 

 

评论

2 楼 Matchstick 2012-06-04  

使用SELECT DISTINCT alias FROM PojoName alias LEFT JOIN FETCH ...
即可解决。

1 楼 dlheart 2012-05-14  

没看懂你什么意思啊，我遇到的问题是一对多，设了fetch = FetchType.eager，结果查出来的对象有重复，是怎么回事啊，但是数据库对象一的一方只有一条数据，多的一方是两天，结果查出来一的一方成了两条数据了，里面的对象是完全一样的