Hibernate中加載的類型有幾種

這篇文章主要講解了“Hibernate中加載的類型有幾種”，文中的講解內(nèi)容簡單清晰，易于學習與理解，下面請大家跟著小編的思路慢慢深入，一起來研究和學習“Hibernate中加載的類型有幾種”吧！

一：Hibernate實體對象的加載

比如說：用戶和訂單的關系是一對多，雖然它們有關聯(lián)，但是默認是延遲加載Lazy=“true”，最終得到的是代理對象，如果要訪問代理對象的屬性的話，則會拋出異常，

解決方法：leftjoinfetch迫切抓取連接

selectufromUseruleftjoinfetchOrdero;

二：Hibernate普通屬性

默認是：lazy=“false”

如果要改為延遲方法較麻煩

三：Hibernate集合對象

setlistmap默認Lazy=“true”

1:List

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

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

key子元素用于映射外鍵列，而map-key子元素則用于映射Map集合的Key。

感謝各位的閱讀，以上就是“Hibernate中加載的類型有幾種”的內(nèi)容了，經(jīng)過本文的學習后，相信大家對Hibernate中加載的類型有幾種這一問題有了更深刻的體會，具體使用情況還需要大家實踐驗證。這里是億速云，小編將為大家推送更多相關知識點的文章，歡迎關注！