一个cascade笔记

在one-to-many设置中通常都是把many放设置位save-update，但这样会出现问题.

比如班级(Classlist)和班级公告(Notify)是一对多的关系

java 代码

Session session = factory.openSession();
    Transaction tx= session.beginTransaction();
    Classlist c = (Classlist) session.load(Classlist.class, 25389l);
    Notify nofity =  new Notify();
    nofity.setClasslist(c);
    c.getNotify().add(nofity);
    nofity.setClasslist(c);
    session.save(nofity);
    tx.commit();
    session.close();

执行的SQL语句:

sql 代码

Hibernate: select classlist0_.id as id0_, classlist0_.className as className0_ from classlist classlist0_ where classlist0_.id=?
Hibernate: select notify0_.classlist_id as classlis7___, notify0_.id as id__, notify0_.id as id3_, notify0_.notify_type as notify_t2_3_, notify0_.title as title3_, notify0_.content as content3_, notify0_.accessory as accessory3_, notify0_.postDate as postDate3_, notify0_.classlist_id as classlis7_3_, notify0_.role_id as role_id3_, role1_.id as id0_, role1_.name as name0_, role1_.uri as uri0_, role1_.classlist_id as classlis4_0_, role1_.user_id as user_id0_, classlist2_.id as id1_, classlist2_.className as className1_, user3_.id as id2_, user3_.USER_TYPE as USER_TYPE2_, user3_.loginID as loginID2_, user3_.password as password2_, user3_.sex as sex2_, user3_.birthday as birthday2_, user3_.realName as realName2_, user3_.nickName as nickName2_, user3_.tel as tel2_, user3_.address as address2_, user3_.describ as describ2_, user3_.studentNumber as student12_2_ from notify notify0_ left outer join role role1_ on notify0_.role_id=role1_.id left outer join classlist classlist2_ on role1_.classlist_id=classlist2_.id left outer join users user3_ on role1_.user_id=user3_.id where notify0_.classlist_id=?
Hibernate: insert into notify (title, content, accessory, postDate, classlist_id, role_id, notify_type) values (?, ?, ?, ?, ?, ?, 'com.talent.domain.Notify')

 

但如果是跨Session，情况就大不一样了.

 

java 代码

Session session = factory.openSession();
        Transaction tx= session.beginTransaction();
        Classlist c = (Classlist) session.load(Classlist.class, 25389l);
        c.getNotify().iterator();
        tx.commit();
        session.close();

        session = factory.openSession();
        tx= session.beginTransaction();
        Notify nofity =  new Notify();
        nofity.setClasslist(c);
        c.getNotify().add(nofity);
        nofity.setClasslist(c);
        session.save(nofity);
        tx.commit();
        session.close();

 

sql 代码

Hibernate: select classlist0_.id as id0_, classlist0_.className as className0_ from classlist classlist0_ where classlist0_.id=?
Hibernate: select notify0_.classlist_id as classlis7___, notify0_.id as id__, notify0_.id as id3_, notify0_.notify_type as notify_t2_3_, notify0_.title as title3_, notify0_.content as content3_, notify0_.accessory as accessory3_, notify0_.postDate as postDate3_, notify0_.classlist_id as classlis7_3_, notify0_.role_id as role_id3_, role1_.id as id0_, role1_.name as name0_, role1_.uri as uri0_, role1_.classlist_id as classlis4_0_, role1_.user_id as user_id0_, classlist2_.id as id1_, classlist2_.className as className1_, user3_.id as id2_, user3_.USER_TYPE as USER_TYPE2_, user3_.loginID as loginID2_, user3_.password as password2_, user3_.sex as sex2_, user3_.birthday as birthday2_, user3_.realName as realName2_, user3_.nickName as nickName2_, user3_.tel as tel2_, user3_.address as address2_, user3_.describ as describ2_, user3_.studentNumber as student12_2_ from notify notify0_ left outer join role role1_ on notify0_.role_id=role1_.id left outer join classlist classlist2_ on role1_.classlist_id=classlist2_.id left outer join users user3_ on role1_.user_id=user3_.id where notify0_.classlist_id=?
Hibernate: insert into notify (title, content, accessory, postDate, classlist_id, role_id, notify_type) values (?, ?, ?, ?, ?, ?, 'com.talent.domain.Notify')
Hibernate: update classlist set className=? where id=?
Hibernate: update notify set title=?, content=?, accessory=?, postDate=?, classlist_id=?, role_id=? where id=?
Hibernate: update notify set title=?, content=?, accessory=?, postDate=?, classlist_id=?, role_id=? where id=?
Hibernate: update notify set title=?, content=?, accessory=?, postDate=?, classlist_id=?, role_id=? where id=?
Hibernate: update notify set title=?, content=?, accessory=?, postDate=?, classlist_id=?, role_id=? where id=?
Hibernate: update notify set title=?, content=?, accessory=?, postDate=?, classlist_id=?, role_id=? where id=?

为什么第二种情况会多了这么多UPDATE呢？

1.因为在classlist被第一个session关闭，classlist变成了游离对象，没有被session关联。
2.在nofity.setClasslist(c)时候，classlist被关联到Session中成为po.
3.因为配置文件中many方设置的cascade选项是save-update,classlist会被结连更新
4.当classlist被更新的时候，由于one方设置的也是save-update,所以和classlist相互关联的notify也会被更新

如果我们把many方设置为none就可以了。

但这样又会产生问题，如果我们保存notify，Hibernate会报一个异常，提示引用了一个未保存的临时对象。

解决的方法可以是每次都保存one的那边.

java 代码

Session session = factory.openSession();
    Transaction tx= session.beginTransaction();
    Classlist c = new Classlist();
    Notify notify =  new Notify();

    c.getNotify().add(notify);
    notify.setClasslist(c);
    session.save(c);
    tx.commit();
    session.close();

sql 代码

insert into classlist (className) values (?)
insert into notify (title, content, accessory, postDate, classlist_id, role_id, notify_type) values (?, ?, ?, ?, ?, ?, 'com.talent.domain.Notify')