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我的使用背景：

v??????? 有新聞和新聞類型，一條新聞只能屬于一個類型，一種新聞類型可以對應多條新聞。

v??????? 在數據庫中，新聞受新聞類型外鍵約束，并可以級聯刪除

v??????? 在 Hibernate 中，實現級聯刪除

v??????? jkakfl

?

（一） 創建數據庫表和關系

DROP? TABLE? NewsType;

CREATE? TABLE NewsType

(

?????? TypeID? NUMBER(10) PRIMARY KEY? NOT NULL,

?????? TypeName? VARCHAR2(400) NOT NULL,

?????? DirName?? VARCHAR2(400) NOT NULL,

?????? TemplateName VARCHAR2(400) NOT NULL

);

DROP? SEQUENCE NEWSTYPE_SEQ;

CREATE? SEQUENCE NEWSTYPE_SEQ? INCREMENT BY 1 START WITH 1;

?

DROP? TABLE? News;

CREATE? TABLE? News

(

?????? NewsID? NUMBER(10) PRIMARY KEY NOT NULL,

??????? TypeID? NUMBER(10) NOT NULL,

?????? Title? VARCHAR2(400) NOT NULL,

?????? HitCount NUMBER(10) DEFAULT? 0 NOT NULL,

?????? IssuseDate? DATE NOT NULL,

?????? DeployerID? NUMBER(10) NOT? NULL,

?????? Origin? VARCHAR2(400)? NOT? NULL,

?????? URL? VARCHAR2(400) NOT NULL,

?????? KEYWORDS VARCHAR(400) ,

??????? Priority? NUMBER(10)? DEFAULT? 0 NOT NULL,

?????? Special? VARCHAR2(400) ,

?????? Description? VARCHAR2(400),

?????? Author? VARCHAR2(400),

?????? Topic?? VARCHAR2(400)

);

DROP SEQUENCE NEWS_SEQ;

CREATE SEQUENCE NEWS_SEQ? INCREMENT BY? 1 START WITH 1;

?

在 oralce 中，設置數據表的約束關系如下圖：

???
???（二） 實現數據表到 POJO 的映射

映射類，我們略去，此處主要顯示配置文件

ü???????? News.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

??????????????????????????? "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<!-- DO NOT EDIT: This is a generated file that is synchronized -->

<!-- by MyEclipse Hibernate tool integration.?????????????????? -->

<!-- Created Fri Nov 11 21:59:47 CST 2005???????????????????????? -->

<hibernate-mapping package="com.scenechina.vr.model">

?????? <class name="News" table="NEWS" lazy="false">

?????? ?????? <id name="newsid" column="NEWSID" type="java.lang.Long">

?????? ?????? ?????? <generator class="sequence">

?????? ?????? ?????? ?????? <param name="sequence">NEWS_SEQ</param>

?????? ?????? ?????? </generator>

?????? ?????? </id>

?????? ?????? <property name="typeid" column="TYPEID" type="java.lang.Long" not-null="true"/>

?????? ?????? <property name="title" column="TITLE" type="java.lang.String" not-null="true"/>

?????? ?????? <property name="hitcount" column="HITCOUNT" type="java.lang.Long" not-null="true"/>

?????? ?????? <property name="issusedate" column="ISSUSEDATE" type="java.util.Date" not-null="true"/>

?????? ?????? <property name="deployerid" column="DEPLOYERID" type="java.lang.Long" not-null="true"/>

?????? ?????? <property name="origin" column="ORIGIN" type="java.lang.String" not-null="true"/>

?????? ?????? <property name="url" column="URL" type="java.lang.String" not-null="true"/>

?????? ?????? <property name="keywords" column="KEYWORDS" type="java.lang.String"/>

?????? ?????? <property name="priority" column="PRIORITY" type="java.lang.Long" not-null="true"/>

?????? ?????? <property name="special" column="SPECIAL" type="java.lang.String"/>

?????? ?????? <property name="description" column="DESCRIPTION" type="java.lang.String"/>

?????? ?????? <property name="author" column="AUTHOR" type="java.lang.String"/>

?????? ?????? <property name="topic" column="TOPIC" type="java.lang.String"/>

?????? ?????? <set name="newsset" cascade="all" inverse="true" lazy="false" order-by="NEWSDETIALID" table="Newsdetials">

?????? ?????? ?????? <key column="newsid"/>

?????? ?????? ?????? <one-to-many class="Newsdetials"/>

?????? ?????? </set>

?????? ?????? <set name="picset" cascade="all" inverse="true" lazy="false" table="Picture">

?????? ?????? ?????? <key column="newsid"/>

?????? ?????? ?????? <one-to-many class="Picture"/>

?????? ?????? </set>

????? ????? <many-to-one name="newstype" column="TYPEID" entity-name="com.model.Newstype" insert="false" update="false"/>

?????? </class>

</hibernate-mapping>

?

ü???????? Newstype.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

??? "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

?????? <!--

??? Created by the Middlegen Hibernate plugin

?

??? http://boss.bekk.no/boss/middlegen/

??? http://hibernate.sourceforge.net/

-->

?????? <class name="com.scenechina.vr.model.Newstype" table="NEWSTYPE" lazy="false">

?????? ?????? <id name="typeid" type="java.lang.Long" column="TYPEID">

?????? ?????? ?????? <generator class="assigned"/>

?????? ?????? </id>

?????? ?????? <property name="typename" type="java.lang.String" column="TYPENAME" not-null="true" length="100"/>

?????? ?????? <property name="dir" type="java.lang.String" column="DIRNAME" not-null="true" length="100"/>

?????? ?????? <property name="templatename" type="java.lang.String" column="TEMPLATENAME" not-null="true" length="100"/>

?????? ?????? <!-- associations -->

????? ????? <set name="news" cascade="all-delete-orphan" inverse="true">

????? ????? ????? <key column="TYPEID"/>

????? ????? ????? <one-to-many class="com.model.News"/>

????? ????? </set>

?????? </class>

</hibernate-mapping>

?

其實這是個雙向以對多關系。

?

（三） 在 DAO 中實現級聯刪除

??????? // 刪除新聞類型記錄

??????? dao.getNewsTypeDAO().deleteObjects(typeIDs);

typeID 是新聞類型的主鍵

執行此操作將會刪除所有此新聞類型的新聞。

news 是一個 Set 類型的變量，用來存放此類型的所有的新聞。

（四） 刪除時遇到的問題

在數據庫中，如果設置了約束關系，那么一定要允許級聯刪除，否則，你在執行刪除時會拋出異常。

如果我們的數據庫關系設置如下：

???畫圈的那個選項沒有選上的話 ，那么我們在執行的時候就會拋出如下的異常：

006-04-06 13:20:16 ERROR [http-8080-Processor23] (JDBCExceptionReporter.java:72

?- ORA-02292: 違反完整約束條件 (SC.NEWS_TYPE_RELATIONS) - 已找到子記錄日志

?

rg.hibernate.exception.ConstraintViolationException: could not execute update q

ery

?????? at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.j

va:69)

?????? at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelp

r.java:43)

?????? at org.hibernate.hql.ast.exec.BasicExecutor.execute(BasicExecutor.java:8

)

?

問題的關鍵在如下兩點：

1.?????? 數據庫中要允許數據表的級聯刪除

2.?????? 在映射文件中要將級聯刪除配置正確

?

?

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