浅谈Hibernate中加载的三种类型

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。

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