javaGrowing

首先一開始我可以獲得一個頻道的channelId，我根據這個channelId得到一個首頁區塊的List，我在hibernate中配置homepagearea的加載方式，這樣就可以通過homepage的到關聯的欄目column(多對一關系)，然后我還是使用hibernate的自動加載，取到column關聯的專題subject(一對多關系)。
這時候問題出來了，由于column到subject的關聯沒有帶channel信息，所以，我取到的subject實際上是一個column下所有的subject，而我期望的是要得到，一個homepagearea下根據channelId和columnId取得的subject.

解決思路：
希望通過hibernate直接建立homepage和subject的1對多關聯關系

解決方法
首先我改變原來利用工具生成的hibernate配置文件和entitybean
先列出原來的homepagearea的配置文件
<?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>
<class
??? name="com.easou.wapsearch.channel.entity.CsHomepageArea"
??? table="CS_HOMEPAGE_AREA"
??? schema="WAPUSER"
??? lazy="true"
>
??? <id
??????? name="id"
??????? type="long"
??????? column="ID"
??????? length="22"
??? >
??? ?<generator class="assigned">
??? ??
??? ?</generator>
??? </id>
??? <property
??????? name="createdBy"
??????? type="long"
??????? column="CREATED_BY"
??????? length="22"
??? />
??? <property
??????? name="createdDate"
??????? type="timestamp"
??????? column="CREATED_DATE"
??????? length="7"
??? />
??? <property
??????? name="isMore"
??????? type="long"
??????? column="IS_MORE"
??????? length="22"
??? />
??? <property
??????? name="name"
??????? type="string"
??????? column="NAME"
??????? length="50"
??? />
??? <property
??????? name="rowCount"
??????? type="long"
??????? column="ROW_COUNT"
??????? length="22"
??? />
??? <property
??????? name="showCount"
??????? type="long"
??????? column="SHOW_COUNT"
??????? length="22"
??? />
??? <property
??????? name="theOrder"
??????? type="long"
??????? column="THE_ORDER"
??????? length="22"
??? />
??? <property
??????? name="updateBy"
??????? type="long"
??????? column="UPDATE_BY"
??????? length="22"
??? />
??? <property
??????? name="updateDate"
??????? type="timestamp"
??????? column="UPDATE_DATE"
??????? length="7"
??? />

??? <!-- Associations -->
??? <!-- bi-directional many-to-one association to CsChannel -->
??? <many-to-one
??????? name="csChannel"???????
??? >
??????? <column name="CHANNEL_ID" length="22"/>
??? </many-to-one>
??? <!-- bi-directional many-to-one association to CsColumn -->
??? <many-to-one
??????? name="csColumn"???????
??? >
??????? <column name="COLUMN_ID" length="22"/>
??? </many-to-one>

</class>
</hibernate-mapping>

為了讓homepagearea和subject形成一種一對多的關系，我增加的一個
<set name="csSubjects" inverse="true" cascade="save-update"
???lazy="false" order-by="THE_ORDER" table="CS_SUBJECT"
???outer-join="true">
???<key>
????<column name="CHANNEL_ID" index="CHANNEL_ID" />
????<column name="COLUMN_ID" index="COLUMN_ID" />
???</key>
???<one-to-many
????class="com.easou.wapsearch.channel.entity.CsSubject" />
</set>
但是由于hibernate一對多映射的一端必須是主鍵，而且我這里需要關聯的還是2列信息，所以我還必須要修改配置文件的主鍵設置
<composite-id mapped="false" unsaved-value="none">
????? <key-many-to-one name="csChannel" column="CHANNEL_ID"></key-many-to-one>
???<key-many-to-one name="csColumn" column="COLUMN_ID"></key-many-to-one>
</composite-id>
并且遮蔽掉原有的channel和column多對一關聯關系，否則會報告重復錯誤
<!-- Associations
?? bi-directional many-to-one association to CsChannel
??<many-to-one name="csChannel" lazy="true">
???<column name="CHANNEL_ID" length="22" />
??</many-to-one>
?? bi-directional many-to-one association to CsColumn
??<many-to-one name="csColumn" lazy="true">
???<column name="COLUMN_ID" length="22" />
??</many-to-one>

??-->
這樣hibernate才會在加載homepagearea時自動把subject的關聯信息也加載進來了

最后的homepagearea配置文件
<?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>
?<class name="com.easou.wapsearch.channel.entity.CsHomepageArea"
??table="CS_HOMEPAGE_AREA" schema="WAPUSER" lazy="true">
??<composite-id mapped="false" unsaved-value="none">
????? <key-many-to-one name="csChannel" column="CHANNEL_ID"></key-many-to-one>
???<key-many-to-one name="csColumn" column="COLUMN_ID"></key-many-to-one>
??</composite-id>
??<property name="createdBy" type="long" column="CREATED_BY"
???length="22" />
??<property name="createdDate" type="timestamp"
???column="CREATED_DATE" length="7" />
??<property name="isMore" type="long" column="IS_MORE"
???length="22" />
??<property name="name" type="string" column="NAME" length="50" />
??<property name="rowCount" type="long" column="ROW_COUNT"
???length="22" />
??<property name="showCount" type="long" column="SHOW_COUNT"
???length="22" />
??<property name="theOrder" type="long" column="THE_ORDER"
???length="22" />
??<property name="updateBy" type="long" column="UPDATE_BY"
???length="22" />
??<property name="updateDate" type="timestamp"
???column="UPDATE_DATE" length="7" />

??<!-- Associations
?? bi-directional many-to-one association to CsChannel
??<many-to-one name="csChannel" lazy="true">
???<column name="CHANNEL_ID" length="22" />
??</many-to-one>
?? bi-directional many-to-one association to CsColumn
??<many-to-one name="csColumn" lazy="true">
???<column name="COLUMN_ID" length="22" />
??</many-to-one>

??-->
??<set name="csSubjects" inverse="true" cascade="save-update"
???lazy="false" order-by="THE_ORDER" table="CS_SUBJECT"
???outer-join="true">
???<key>
????<column name="CHANNEL_ID" index="CHANNEL_ID" />
????<column name="COLUMN_ID" index="COLUMN_ID" />
???</key>
???<one-to-many
????class="com.easou.wapsearch.channel.entity.CsSubject" />

??</set>

?</class>

</hibernate-mapping>

經驗總結：
1、本來使用hibernate的加載策略就是為了把一些業務邏輯直接融合在數據庫關系當中，但是由于自己邏輯沒有考慮清楚造成了加載時信息的丟失(而且我覺得我的表結構有問題，不知有有沒有dba給我指點一下問題)。
2、hibernate的一對多關聯關系多端是1端是針對主鍵的，所以不論你是關聯的是1列2列還是3列，它們都應該是你的1端的主鍵或者聯合主鍵(其實一對一，多對一，多對多的原理也是相似的)。

參考資料：hibernate_reference(3.2)