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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1. Hibernate中generator属性的意义
2. hibernate Key Generator 主键生成方式
3. Hibernate的主键生成机制
4. hibernate的Query cache
5. Hibernate中hbm的generator属性