????????????????? hibernate繼承關(guān)系映射大概有5種,這5種繼承關(guān)系映射里面,我覺得最有效最常用的一種方式非常好.就說說這種吧.先來說說hibernate繼承關(guān)系什么時(shí)候使用.
???????????? (1)?hibernate繼承關(guān)系什么時(shí)候使用?
???????????? 很多例子都是說一個(gè)動(dòng)物類,然后是老虎類啊,獅子類啊之類去繼承動(dòng)物類.例子很好,但是實(shí)際應(yīng)用中我根據(jù)這個(gè)提出了一個(gè)完全可行的解決方案,很有成就感!
???????????? 在項(xiàng)目里面,遇到這樣一個(gè)問題,大概有30多張表,里面都有共性的字段,每張表都需要走審核流程,如果針對(duì)每張表都做相應(yīng)的審核模塊,代碼重復(fù)不說,那工作量就大了.針對(duì)這個(gè)就需要用到hibernate繼承關(guān)系映射了,所有共性的字段都提取出來,把審核模塊做成公共的模塊!這中間又涉及用到了java反射機(jī)制.
??????????? (2)開始例子
??????????? 先把30多張表共性的字段整理出來, id主鍵字段(String 類型的 主鍵生成方式是uuid),因?yàn)閡uid按著計(jì)算,據(jù)說得300年才能出現(xiàn)重復(fù)的數(shù)據(jù),300年以后我早就入古了,軟件維護(hù)找我,嘿嘿,連骨灰都沒嘍!得了,跑題了.......繼續(xù)!
????????? 共有的字段:
???????? id???? varchar?? 32
???????? fileName?? varchar? 100
??????? audState??? varchar? 2
??????? tableName? varchar? 50 (這個(gè)字段存表名,表1的名字table1,就存table1,表2的名字table2,就存table2......反射時(shí)候用)
????????? 上面是所有表中共有的字段.再拿30多張表中的一張table1表來舉例子吧.table1表里面自己特有的字段如下:
???????? isDel?? varchar? 2
??????? fileTypeId?? int????4
??????? code1?? varchar?? 50
??????? code2?? varchar? 50
??????? code3?? varchar? 50
?????????hibenrate繼承關(guān)系映射開始了
??????? 把共有的字段提出來做一個(gè)配置文件TcommTable.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"
>
<!--
?
????Mapping?file?autogenerated?by?MyEclipse?-?Hibernate?Tools
-->
<
hibernate-mapping
>
????
<
class?
name
="com.hibernate.po.TcommTable"
?abstract
="true"
?dynamic-insert
="true"
>
????????
<
id?
name
="id"
?type
="string"
>
????????????
<
column?
name
="id"
?
/>
????????????
<
generator?
class
="uuid"
?
/>
????????
</
id
>
????????
<
property?
name
="fileName"
?type
="string"
>
????????????
<
column?
name
="fileName"
?length
="100"
?
/>
????????
</
property
>
????????
????????
<
property?
name
="audState"
?type
="string"
>
????????????
<
column?
name
="audState"
?length
="2"
?
/>
????????
</
property
>
????????
?
<
property?
name
="tableName"
?type
="string"
?insert
="false"
>
????????????
<
column?
name
="tableName"
?length
="32"
?
/>
????????
</
property
>
????
</
class
>
</
hibernate-mapping
>
上面的配置文件是抽象的abstract ="true" ?.
要生成相應(yīng)的po:
??????? public abstract class TcommTable implements Serializable {
??????????????? private String id;
??????????????? private String fileName;
???????????????private String tableName;
????????????? //生成set/get()方法
??????? }
table1表特有的字段生成配置文件和po,都是TcommTable 的子類
table1表的配置文件Table1.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"
>
<!--
?
????Mapping?file?autogenerated?by?MyEclipse?-?Hibernate?Tools
-->
<
hibernate-mapping
>
????
<
union-subclass?
name
="com.hibernate.po.Table1"
?table
="Table1"
?extends
="com.hibernate.po.TcommTable "
>
??????
????????????
????????????
<
property?
name
="isDel"
?type
="string"
>
????????????????
<
column?
name
="isDel"
?length
="2"
?
/>
????????????
</
property
>
????????????????
<
column?
name
="fileTypeId"
?
/>
????????????
</
property
>
????????????????
<
column?
name
="code1"
?length
="50"
?
/>
????????????
</
property
>
????????????????
<
column?
name
="code2"
?length
="50"
?
/>
????????????
</
property
>
????????????????
<
column?
name
="code3"
?length
="50"
?
/>
????????????
</
property
>
???
??????
</
union-subclass
>
</
hibernate-mapping
>
?
??table1的po:
????public class Table1? extends TcommTable {
?????????????????private String isDel;????
???????????????? private String fileTypeId;
???????????????? private String code1;
???????????????? private String code2;
??????????????? ?private String code3;
???????????????? //生成set/get()方法
??????? }
?????? (2)運(yùn)用java的反射機(jī)制實(shí)現(xiàn)模塊的共用性
?????? 當(dāng)30多張表公用一個(gè)審核模塊的時(shí)候,把抽象類TcommTable傳到審核模塊,如何知道這個(gè)抽象類是那張具體的表呢?就用到了java反射機(jī)制了,因?yàn)槌橄箢悷o法new出對(duì)象來,所以就要用java反射機(jī)制.
????? 在審核的action里面實(shí)現(xiàn)java的反射機(jī)制,主要代碼如下:
???? String tableName = request.getParameter("tableName");
???? String allName = "com.hibernate.po." + tableName;
??? TcommTable?tomm = (TcommTable) Class.forName(allName).newInstance();
????這樣,就能得到table1所有的字段(公共字段和table1特有的字段),然后把要審核的內(nèi)容放進(jìn)tomm這個(gè)對(duì)象里面就行了.注意,java反射機(jī)制必須要帶上類的完整包名,否則反射出錯(cuò).tableName字段是區(qū)分30多張表的識(shí)別字段,通過這個(gè)字段,hibernate就自動(dòng)可以判斷出是哪個(gè)表和相應(yīng)的類了,然后通過反射就能得到相應(yīng)類的所有字段了,因?yàn)楣沧侄畏旁谝粋€(gè)抽象類里面,抽象類無法new對(duì)象,所以只能通過反射機(jī)制來實(shí)現(xiàn)了.
?
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