Hibernate的一对一联系关系实例<转>

Hibernate的一对一关联实例<转>

Hibernate的一对一关联实例

Hibernate中的表的关联有一对一，一对多和多对多三种关联方式，在这篇笔记和接下来的笔记中，我将用我自己的实际例子来说明如何具体实施。
??????我使用的Hibernate版本是2.1.8，在Hibernate的网站2.1.6版本的中文文档中有关一对一的关联有下面一段表述：

5.1.11.?一对一
持久化对象之间一对一的关联关系是通过one-to-one元素定义的。?

<one-to-one
????????name="propertyName"????????????????????????????????(1)
????????class="ClassName"??????????????????????????????????(2)
????????cascade="all|none|save-update|delete"??????????????(3)
????????constrained="true|false"???????????????????????????(4)
????????outer-join="true|false|auto"???????????????????????(5)
????????property-ref="propertyNameFromAssociatedClass"?????(6)
????????access="field|property|ClassName"??????????????????(7)
????????
/>
(1)?name:?属性的名字。?
?
(2)?class?(可选?-?默认是通过反射得到的属性类型)：被关联的类的名字。?
?
(3)?cascade(级联)?(可选)?表明操作是否从父对象级联到被关联的对象。?
?
(4)?constrained（约束）?(可选)?表明该类对应的表对应的数据库表，和被关联的对象所对应的数据库表之间，通过一个外键引用对主键进行约束。这个选项影响save()和delete()在级联执行时的先后顺序（也在schema?export?tool中被使用）。?
?
(5)?outer-join（外连接）?(可选?-?默认为?自动):?当设置hibernate.use_outer_join的时候，对这个关联允许外连接抓取。?
?
(6)?property-ref:?(可选)?指定关联类的一个属性，这个属性将会和本外键相对应。如果没有指定，会使用对方关联类的主键。?
?
(7)?access?(可选?-?默认是?property):?Hibernate用来访问属性的策略。?
?

有两种不同的一对一关联：?

主键关联?

惟一外键关联?

主键关联不需要额外的表字段;两行是通过这种一对一关系相关联的，那么这两行就共享同样的主关键字值。所以如果你希望两个对象通过主键一对一关联，你必须确认它们被赋予同样的标识值！?

比如说，对下面的Employee和Person进行主键一对一关联:?

<one-to-one?name="person"?class="Person"/>
<one-to-one?name="employee"?class="Employee"?constrained="true"/>
现在我们必须确保PERSON和EMPLOYEE中相关的字段是相等的。我们使用一个特别的称为foreign的Hibernate标识符生成器策略：?

<class?name="person"?table="PERSON">
????<id?name="id"?column="PERSON_ID">
????????<generator?class="foreign">
????????????<param?name="property">employee</param>
????????</generator>
????</id>
????
????<one-to-one?name="employee"
????????class="Employee"
????????constrained="true"/>
</class>
一个刚刚保存的Person实例被赋予和该Person的employee属性所指向的Employee实例同样的关键字值。?

另一种方式是一个外键和一个惟一关键字对应，上面的Employee和Person的例子，如果使这种关联方式，应该表达成：?

<many-to-one?name="person"?class="Person"?column="PERSON_ID"?unique="true"/>
如果在Person的映射加入下面几句，这种关联就是双向的：?

<one-to-one?name"employee"?class="Employee"?property-ref="person"/>
??????
??????下面是我的一个一对一主键关联的例子，使用的数据库是MySQL 4.1.11：
??????我有两个表：UserBasic和UserInfo，UserBasic记录的是用户的基本注册信息，UserInfo表记录的是用户的详细信息。表的结构如下：

?1CREATE?TABLE?IF?NOT?EXISTS?UserBasic
?2(
?3???Guid???????????????????????????INT????????????????????????????NOT?NULL?AUTO_INCREMENT,
?4???Account????????????????????????VARCHAR(64)????????????????????NOT?NULL,
?5???Password???????????????????????VARCHAR(16)????????????????????NOT?NULL,
?6???Email??????????????????????????VARCHAR(128)???????????????????NOT?NULL,
?7???PRIMARY?KEY?(Guid)
?8)?TYPE=InnoDB;
?9
10CREATE?TABLE?IF?NOT?EXISTS?UserInfo
11(
12???Guid???????????????????????????INT????????????????????????????NOT?NULL,
13???Username???????????????????????VARCHAR(128),
14???Gender?????????????????????????CHAR(1),
15???Birthday???????????????????????DATETIME,
16???PRIMARY?KEY?(Guid)
17)?TYPE=InnoDB;
18
19ALTER?TABLE?UserInfo?ADD?CONSTRAINT?UserInfoRFUserBasic?FOREIGN?KEY?(Guid)?
20???REFERENCES?UserBasic?(Guid)?ON?DELETE?CASCADE?ON?UPDATE?RESTRICT;
??????UserInfo的主键值和UserBasic的主键值是一样的，两个表是单向的一对一关系。UserBasic为主控方，UserInfo是被动方。
??????用Middlegen生成的UserBasic.hbm.xml文件，修改后的内容如下：

??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.UserBasic"?
?16????table="UserBasic"
?17????dynamic-update="true"
?18????dynamic-insert="true"
?19>
?20????<meta?attribute="class-description"?inherit="false">
?21???????@hibernate.class
?22????????table="UserBasic"
?23????????dynamic-update="true"
?24????????dynamic-insert="true"
?25????</meta>
?26
?27????<id
?28????????name="guid"
?29????????type="int"
?30????????column="Guid"
?31????>
?32????????<meta?attribute="field-description">
?33???????????@hibernate.id
?34????????????generator-alt="Hibernate的一对一联系关系实例<转>" src="//img.reader8.net/uploadfile/jiaocheng/20140188/3040/201401301440589455.gif">????????????type="int"
?36????????????column="Guid"
?37
?38
?39????????</meta>
?40????????<generator?class="native"?/>
?41????</id>
?42
?43????<property
?44????????name="account"
?45????????type="java.lang.String"
?46????????column="Account"
?47????????not-null="true"
?48????????length="64"
?49????>
?50????????<meta?attribute="field-description">
?51???????????@hibernate.property
?52????????????column="Account"
?53????????????length="64"
?54????????????not-null="true"
?55????????</meta>????
?56????</property>
?57????<property
?58????????name="password"
?59????????type="java.lang.String"
?60????????column="Password"
?61????????not-null="true"
?62????????length="16"
?63????>
?64????????<meta?attribute="field-description">
?65???????????@hibernate.property
?66????????????column="Password"
?67????????????length="16"
?68????????????not-null="true"
?69????????</meta>????
?70????</property>
?71????<property
?72????????name="email"
?73????????type="java.lang.String"
?74????????column="Email"
?75????????not-null="true"
?76????????length="128"
?77????>
?78????????<meta?attribute="field-description">
?79???????????@hibernate.property
?80????????????column="Email"
?81????????????length="128"
?82????????????not-null="true"
?83????????</meta>????
?84????</property>
?85
?86????<!--?Associations?-->
?87??
?88????<!--?bi-directional?one-to-one?association?to?UserInfo?-->
?89????<one-to-one
?90????????name="userInfo"
?91????????class="com.xxx.hibernate.UserInfo"
?92????????cascade="save-update"
?93????>
?94????????<meta?attribute="field-description">
?95???????????@hibernate.one-to-one
?96???????????????alt="Hibernate的一对一联系关系实例<转>" src="//img.reader8.net/uploadfile/jiaocheng/20140188/3040/201401301440589455.gif">????????????cascade="save-update"
?98????????</meta>
?99????</one-to-one>
100
101</class>
102</hibernate-mapping>
??????由于在建立外键的时候就声明了ON DELETE CASCADE，所以在xml的配置文件中第97行声明为save-update。如果声明为all，那么在删除UserBasic表的数据时，会无谓的多出一条删除UserInfo的delete语句出来。
??????UserInfo.hbm.xml文件的内容如下：

?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.UserInfo"?
16????table="UserInfo"
17????dynamic-update="true"
18????dynamic-insert="true"
19>
20????<meta?attribute="class-description"?inherit="false">
21???????@hibernate.class
22????????table="UserInfo"
23????????dynamic-update="true"
24????????dynamic-insert="true"
25????</meta>
26
27????<id
28????????name="guid"
29????????type="int"
30????????column="Guid"
31????>
32????????<meta?attribute="field-description">
33???????

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