假設Team和Student是1對多的關系，而student中只有team_id和name兩個屬性，我們可以不建立Student實體類，采用element的方式，由于bag可以允許重復，所以，在我們根據team刪除其下某一個student的時候，hibernate不知道具體要刪除哪一條數據，所以，只有講team下所有student全部刪除，然后再重新插入不應該刪除的數據，這樣會對效率有很大影響，針對這種情況，可以采用idbag標簽，在student中加一個字段cid來唯一標識每一個student
數據庫結構：
?
create
?
table
?teamIDBag?(id?
varchar
(
32
),teamname?
varchar
(
32
));
create
?
table
?studentIDBag(team_id?
varchar
(
32
),name?
varchar
(
32
),cid?
varchar
(
32
));
Pojo:
?
package
?Collection.IDBag;
import
?java.util.ArrayList;
import
?java.util.List;
import
?java.util.Map;
public
?
class
?Team?
{
???
private
?String?id;
???
private
?String?teamname;
???
private
?List?students
=
new
?ArrayList();
public
?String?getId()?
{
????
return
?id;
}
public
?
void
?setId(String?id)?
{
????
this
.id?
=
?id;
}
public
?String?getTeamname()?
{
????
return
?teamname;
}
public
?
void
?setTeamname(String?teamname)?
{
????
this
.teamname?
=
?teamname;
}
public
?List?getStudents()?
{
????
return
?students;
}
public
?
void
?setStudents(List?students)?
{
????
this
.students?
=
?students;
}
}
?Team.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"
>
<!--
?
????Mapping?file?autogenerated?by?MyEclipse?-?Hibernate?Tools
-->
<
hibernate-mapping
>
<
class?
name
="Collection.IDBag.Team"
?table
="teamIDBag"
?
>
????
<
id?
name
="id"
?unsaved-value
="null"
>
??????
<
generator?
class
="uuid.hex"
></
generator
>
????
</
id
>
????
<
property?
name
="teamname"
?type
="string"
?column
="teamname"
></
property
>
???
????
<
idbag?
name
="students"
?table
="studentIDBag"
?cascade
="all,delete-orphan"
?
>
??????
<
collection-id?
type
="string"
?column
="cid"
>
????????
<
generator?
class
="uuid.hex"
></
generator
>
??????
</
collection-id
>
??????
<
key?
column
="team_id"
></
key
>
??????
<
element?
type
="string"
?column
="name"
></
element
>
????
</
idbag
>
</
class
>
</
hibernate-mapping
>
?
Hibernate.cfg.xml
?
<?
xml?version='1.0'?encoding='UTF-8'
?>
<!
DOCTYPE?hibernate-configuration?PUBLIC
??????????"-//Hibernate/Hibernate?Configuration?DTD?3.0//EN"
??????????"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"
>
<!--
?Generated?by?MyEclipse?Hibernate?Tools.???????????????????
-->
<
hibernate-configuration
>
<
session-factory
>
????
<
property?
name
="connection.username"
>
root
</
property
>
????
<
property?
name
="connection.url"
>
????????jdbc:mysql://localhost:3306/schoolproject?characterEncoding=gb2312
&
useUnicode=true
????
</
property
>
????
<
property?
name
="dialect"
>
????????org.hibernate.dialect.MySQLDialect
????
</
property
>
????
<
property?
name
="myeclipse.connection.profile"
>
mysql
</
property
>
????
<
property?
name
="connection.password"
>
1234
</
property
>
????
<
property?
name
="connection.driver_class"
>
????????com.mysql.jdbc.Driver
????
</
property
>
????
<
property?
name
="hibernate.dialect"
>
????????org.hibernate.dialect.MySQLDialect
????
</
property
>
????
<
property?
name
="hibernate.show_sql"
>
true
</
property
>
????
<
property?
name
="current_session_context_class"
>
thread
</
property
>
????
<
property?
name
="jdbc.batch_size"
>
15
</
property
>
????
<
mapping?
resource
="Collection/IDBag/Team.hbm.xml"
?
/>
</
session-factory
>
</
hibernate-configuration
>
?
測試代碼：
?
package
?Collection.IDBag;
import
?java.io.File;
import
?java.util.Map;
import
?org.hibernate.Session;
import
?org.hibernate.SessionFactory;
import
?org.hibernate.Transaction;
import
?org.hibernate.cfg.Configuration;
public
?
class
?Test?
{
????
public
?
static
?
void
?main(String[]?args)?
{
????????String?filePath
=
System.getProperty(
"
user.dir
"
)
+
File.separator
+
"
src/Collection/IDBag
"
+
File.separator
+
"
hibernate.cfg.xml
"
;
????????File?file
=
new
?File(filePath);
????????System.out.println(filePath);
????????SessionFactory?sessionFactory
=
new
?Configuration().configure(file).buildSessionFactory();
????????Session?session
=
sessionFactory.openSession();
????????Transaction?t
=
session.beginTransaction();
????????
????
????????
//
????????Team?team1=new?Team();
//
????????team1.setTeamname("team1");
//
????????
//
????????Team?team2=new?Team();
//
????????team2.setTeamname("team2");
//
????????
//
???????
//
???????
//
//
????????
//
由于Bag映射可以重復，所以這里重復保存student
//
????????team1.getStudents().add("tom1");
//
????????team1.getStudents().add("tom1");
//
????????team2.getStudents().add("tom2");
//
????????
//
????????
//
????????
//
????????session.save(team1);
//
????????session.save(team2);
????????
????????Team?t1
=
(Team)session.createQuery(
"
from?Team?t?where?t.teamname='team1'
"
).uniqueResult();
????????t1.getStudents().remove(
0
);
????????t.commit();
????????
????}
}
?
運行結果：
Hibernate: select team0_.id as id0_, team0_.teamname as teamname0_ from teamIDBag team0_ where team0_.teamname='team1'
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_, students0_.cid as cid0_ from studentIDBag students0_ where students0_.team_id=?
Hibernate: delete from studentIDBag where cid=?
可以紅色部分，刪除student時是根據cid刪的，如果不使用idbag,則會出類似delete from studentIDBag where team_id=?的操作，然后會接著跟一個insert操作，來恢復本不應該刪除的數據
更多文章、技術交流、商務合作、聯系博主
微信掃碼或搜索：z360901061
微信掃一掃加我為好友
QQ號聯系： 360901061
您的支持是博主寫作最大的動力，如果您喜歡我的文章，感覺我的文章對您有幫助，請用微信掃描下面二維碼支持博主2元、5元、10元、20元等您想捐的金額吧，狠狠點擊下面給點支持吧，站長非常感激您！手機微信長按不能支付解決辦法：請將微信支付二維碼保存到相冊，切換到微信，然后點擊微信右上角掃一掃功能，選擇支付二維碼完成支付。
【本文對您有幫助就好】元
