Hibernate中加载的类型有几种

这篇文章主要讲解了“Hibernate中加载的类型有几种”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“Hibernate中加载的类型有几种”吧！

一：Hibernate实体对象的加载

比如说：用户和订单的关系是一对多，虽然它们有关联，但是默认是延迟加载Lazy=“true”，最终得到的是代理对象，如果要访问代理对象的属性的话，则会抛出异常，

解决方法：leftjoinfetch迫切抓取连接

selectufromUseruleftjoinfetchOrdero;

二：Hibernate普通属性

默认是：lazy=“false”

如果要改为延迟方法较麻烦

三：Hibernate集合对象

setlistmap默认Lazy=“true”

1:List

Java代码  <listnamelistname="diarys"table="petDiary"cascade="all"inverse="true"> <keycolumnkeycolumn="petId"></key> <indexcolumnindexcolumn="listindex"></index> <one-to-manyclassone-to-manyclass="com.lovo.po.PetDiary"/> </list>  <listnamelistname="diarys"table="petDiary"cascade="all"inverse="true">   <keycolumnkeycolumn="petId"></key>   <indexcolumnindexcolumn="listindex"></index>   <one-to-manyclassone-to-manyclass="com.lovo.po.PetDiary"/> </list>

2:set

Java代码  <setnamesetname="orders" table="t_order" cascade="all" inverse="true" lazy="true" > <keycolumnkeycolumn="fk_customer_id"></key> <one-to-manyclassone-to-manyclass="Order"/> </set>  <setnamesetname="orders" table="t_order" cascade="all" inverse="true" lazy="true" > <keycolumnkeycolumn="fk_customer_id"></key> <one-to-manyclassone-to-manyclass="Order"/> </set>

3:map

Java代码  privateMapschool=newHashMap();   publicMapgetSchool(){  returnschool;  }  publicvoidsetSchool(Mapschool){  this.school=school;  }   privateMapschool=newHashMap();   publicMapgetSchool(){  returnschool;  }  publicvoidsetSchool(Mapschool){  this.school=school;  }

Xml代码  <mapnamemapname="school"table="schools"> <keycolumnkeycolumn="pid"not-null="true"/> <map-keytypemap-keytype="string"column="indet"/> <elementtypeelementtype="float"column="score"/> </map>  privateMapschool=newHashMap();   publicMapgetSchool(){  returnschool;  }  publicvoidsetSchool(Mapschool){  this.school=school;  }   privateMapschool=newHashMap();   publicMapgetSchool(){  returnschool;  }  publicvoidsetSchool(Mapschool){  this.school=school;  }

Xml代码  <mapnamemapname="school"table="schools"> <keycolumnkeycolumn="pid"not-null="true"/> <map-keytypemap-keytype="string"column="indet"/> <elementtypeelementtype="float"column="score"/> </map>

key子元素用于映射外键列，而map-key子元素则用于映射Map集合的Key。

感谢各位的阅读，以上就是“Hibernate中加载的类型有几种”的内容了，经过本文的学习后，相信大家对Hibernate中加载的类型有几种这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！