浅谈Hibernate中加载的三种类型

一：Hibernate实体对象的加载

专注于为中小企业提供成都网站设计、成都做网站服务,电脑端+手机端+微信端的三站合一,更高效的管理,为中小企业洛南免费做网站提供优质的服务。我们立足成都，凝聚了一批互联网行业人才，有力地推动了成百上千企业的稳健成长，帮助中小企业通过网站建设实现规模扩充和转变。

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。