內蒙古java團隊

??????
??????我的例子是一個全國省和市的數據表，省為一個表，市為一個表，所使用的數據庫是MySQL 4.1.11。表的結構如下：

?1 CREATE ? TABLE ? IF ? NOT ? EXISTS ?Province
?2 (
?3 ???Guid??????????????????????????? INT ???????????????????????????? NOT ? NULL ?AUTO_INCREMENT,
?4 ???Provincename??????????????????? VARCHAR ( 16 )???????????????????? NOT ? NULL ,
?5 ??? PRIMARY ? KEY ?(Guid)
?6 )?TYPE = InnoDB;
?7
?8 CREATE ? TABLE ? IF ? NOT ? EXISTS ?City
?9 (
10 ???Guid??????????????????????????? INT ???????????????????????????? NOT ? NULL ?AUTO_INCREMENT,
11 ???Cityname??????????????????????? VARCHAR ( 32 )???????????????????? NOT ? NULL ,
12 ???ProvinceID????????????????????? INT ???????????????????????????? NOT ? NULL ,
13 ??? PRIMARY ? KEY ?(Guid)
14 )?TYPE = InnoDB;
15
16 ALTER ? TABLE ?City? ADD ? CONSTRAINT ?CityRFProvince? FOREIGN ? KEY ?(ProvinceID)?
17 ??? REFERENCES ?Province?(Guid)? ON ? DELETE ? CASCADE ? ON ? UPDATE ? RESTRICT ;

Province表做為主控方，City表做為被控方，兩者之間是雙向的一對多關系。用Middlegen生成的Province.hbm.xml文件，修改后的內容如下：

?1 <? xml?version="1.0" ?>
?2 <! DOCTYPE?hibernate-mapping?PUBLIC
?3 ????"-//Hibernate/Hibernate?Mapping?DTD?2.0//EN"
?4 ????"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"? >
?5 ????
?6 < hibernate-mapping >
?7 <!-- ?
?8 ????Created?by?the?Middlegen?Hibernate?plugin?2.1
?9
10 ????http://boss.bekk.no/boss/middlegen/
11 ????http://www.hibernate.org/
12 -->
13
14 < class?
15 ???? name ="com.xxx.hibernate.Province" ?
16 ????table ="Province"
17 >
18 ???? < meta? attribute ="class-description" ?inherit ="false" >
19 ???????@hibernate.class
20 ????????table="Province"
21 ???? </ meta >
22
23 ???? < id
24 ???????? name ="guid"
25 ????????type ="int"
26 ????????column ="Guid"
27 ???? >
28 ???????? < meta? attribute ="field-description" >
29 ???????????@hibernate.id
30 ????????????generator-class="native"
31 ????????????type="int"
32 ????????????column="Guid"
33
34
35 ???????? </ meta >
36 ???????? < generator? class ="native" ? />
37 ???? </ id >
38
39 ???? < property
40 ???????? name ="provincename"
41 ????????type ="java.lang.String"
42 ????????column ="Provincename"
43 ????????not-null ="true"
44 ????????length ="16"
45 ???? >
46 ???????? < meta? attribute ="field-description" >
47 ???????????@hibernate.property
48 ????????????column="Provincename"
49 ????????????length="16"
50 ????????????not-null="true"
51 ???????? </ meta > ????
52 ???? </ property >
53
54 ???? <!-- ?Associations? -->
55 ??
56 ???? <!-- ?bi-directional?one-to-many?association?to?City? -->
57 ???? < set
58 ???????? name ="cities"
59 ????????lazy ="true"
60 ????????inverse ="true"
61 ????????cascade ="save-update"
62 ???? >
63 ???????? < meta? attribute ="field-description" >
64 ???????????@hibernate.set
65 ????????????lazy="true"
66 ????????????inverse="true"
67 ????????????cascade="save-update"
68
69 ???????????@hibernate.collection-key
70 ????????????column="ProvinceID"
71
72 ???????????@hibernate.collection-one-to-many
73 ????????????class="com.xxx.hibernate.City"
74 ???????? </ meta >
75 ???????? < key >
76 ???????????? < column? name ="ProvinceID" ? />
77 ???????? </ key >
78 ???????? < one-to-many?
79 ???????????? class ="com.xxx.hibernate.City"
80 ???????? />
81 ???? </ set >
82
83 </ class >
84 </ hibernate-mapping >
85

??????由于在建立外鍵的時候就聲明了ON DELETE CASCADE，所以在xml的配置文件中cascade聲明為save-update。如果聲明為all，那么在刪除Province表的數據時，會無謂的多出一條刪除City的delete語句出來，這將會影響程序的性能。
??????City.hbm.xml的內容如下：

1<?xml?version="1.0"?>
?2<!DOCTYPE?hibernate-mapping?PUBLIC
?3????"-//Hibernate/Hibernate?Mapping?DTD?2.0//EN"
?4????"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"?>
?5????
?6<hibernate-mapping>
?7<!--?
?8????Created?by?the?Middlegen?Hibernate?plugin?2.1
?9
10????http://boss.bekk.no/boss/middlegen/
11????http://www.hibernate.org/
12-->
13
14<class?
15????name="com.xxx.hibernate.City"?
16????table="City"
17>
18????<meta?attribute="class-description"?inherit="false">
19???????@hibernate.class
20????????table="City"
21????</meta>
22
23????<id
24????????name="guid"
25????????type="int"
26????????column="Guid"
27????>
28????????<meta?attribute="field-description">
29???????????@hibernate.id
30????????????generator-class="native"
31????????????type="int"
32????????????column="Guid"
33
34
35????????</meta>
36????????<generator?class="native"?/>
37????</id>
38
39????<property
40????????name="cityname"
41????????type="java.lang.String"
42????????column="Cityname"
43????????not-null="true"
44????????length="32"
45????>
46????????<meta?attribute="field-description">
47???????????@hibernate.property
48????????????column="Cityname"
49????????????length="32"
50????????????not-null="true"
51????????</meta>????
52????</property>
53
54????<!--?Associations?-->
55??
56????<!--?bi-directional?many-to-one?association?to?Province?-->
57????<many-to-one
58????????name="province"
59????????class="com.xxx.hibernate.Province"
60????????cascade="none"
61????????outer-join="auto"
62????????update="true"
63????????insert="true"
64????????access="property"
65????????not-null="true"
66????>
67????????<meta?attribute="field-description">
68???????????@hibernate.many-to-one
69????????????cascade="none"
70????????????outer-join="auto"
71????????????update="true"
72????????????insert="true"
73????????????access="property"
74????????????not-null="true"
75???????????@hibernate.column?name="ProvinceID"?????????
76????????</meta>
77????????<column?name="ProvinceID"?/>
78????</many-to-one>
79
80</class>
81</hibernate-mapping>
82

many-to-one節點有以下屬性（摘自Hibernate文檔）：

(1)	name: 屬性名。
(2)	column (可選): 字段名。
(3)	class (可選 - 默認是通過反射得到屬性類型): 關聯的類的名字。
(4)	cascade（級聯） (可選): 指明哪些操作會從父對象級聯到關聯的對象。
(5)	outer-join（外連接） (可選 - 默認為 自動): 當設置hibernate.use_outer_join的時候，對這個關聯允許外連接抓取。
(6)	update, insert (可選 - defaults to true) 指定對應的字段是否在用于UPDATE 和/或 INSERT的SQL語句中包含。如果二者都是false,則這是一個純粹的“外源性（derived）”關聯，它的值是通過映射到同一個（或多個）字段的某些其他屬性得到的，或者通過trigger(除法器），或者是其他程序。
(7)	property-ref: (可選) 指定關聯類的一個屬性，這個屬性將會和本外鍵相對應。如果沒有指定，會使用對方關聯類的主鍵。
(8)	access (可選 - 默認是 property): Hibernate用來訪問屬性的策略。

cascade 屬性允許下列值： all, save-update, delete, none。設置除了none以外的其它值會傳播特定的操作到關聯的（子）對象中。參見后面的“Lifecycle Objects(自動管理生命周期的對象）”。

outer-join 參數允許下列三個不同值：

• auto (默認) 使用外連接抓取關聯（對象），如果被關聯的對象沒有代理(proxy)

• true 一直使用外連接來抓取關聯

• false 永遠不使用外連接來抓取關聯

??????用hbm2java生成對應的對應的Java類：hbm2java *.xml --output=xxx。
??????Hibernate的配置文件hibernate.cfg.xml內容如下：

1<?xml?version="1.0"?encoding="utf-8"?>
?2<!DOCTYPE?hibernate-configuration
?3????PUBLIC?"-//Hibernate/Hibernate?Configuration?DTD//EN"
?4????"http://hibernate.sourceforge.net/hibernate-configuration-2.0.dtd">
?5
?6<hibernate-configuration>
?7????<session-factory>
?8
?9????????<!--?local?connection?properties?-->
10????????<property?name="hibernate.connection.url">jdbc:mysql://127.0.0.1/xxx?useUnicode=true&amp;characterEncoding=UTF-8&amp;autoReconnect=true</property>
11????????<property?name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
12????????<property?name="hibernate.connection.username">root</property>
13????????<property?name="hibernate.connection.password">123456</property>
14????????<!--?property?name="hibernate.connection.pool_size"></property?-->
15
16????????<!--?dialect?for?MySQL?-->
17????????<property?name="dialect">net.sf.hibernate.dialect.MySQLDialect</property>
18
19????????<property?name="hibernate.show_sql">true</property>
20????????<property?name="hibernate.use_outer_join">true</property>
21????????<property?name="hibernate.transaction.factory_class">net.sf.hibernate.transaction.JDBCTransactionFactory</property>
22????????
23????????<mapping?resource="com/xxx/hibernate/City.hbm.xml"/>
24????????<mapping?resource="com/xxx/hibernate/Province.hbm.xml"/>
25
26????</session-factory>
27</hibernate-configuration>

JUnit的測試用例程序片斷如下：

?1 ???? public ? void ?testInsert()? {
?2 ???????? try ? {
?3 ????????????Province?province? = ? new ?Province();
?4 ????????????province.setProvincename( " 廣東 " );
?5 ????????????
?6 ????????????City?city? = ? new ?City();
?7 ????????????city.setCityname( " 深圳 " );
?8 ????????????
?9 ????????????city.setProvince(province);
10 ????????????province.setCities( new ?HashSet());
11 ????????????province.getCities().add(city);
12 ????????????
13 ????????????Transaction?tx? = ?session.beginTransaction();
14 ????????????session.save(province);
15 ????????????tx.commit();
16 ????????} ? catch ?(HibernateException?e)? {
17 ????????????e.printStackTrace();
18 ????????} ? catch ?(Exception?ex)? {
19 ????????????ex.printStackTrace();
20 ????????}
21 ????}

運行測試程序，可以看到輸出了兩條insert語句，省的值和市的值都插入到了表中。