浅析Hibernate映射（二）——关系映射（3）

双向一对一关联映射

与单向一对一关联映射一样，双向映射依然可以采用两种方式实现：1、主键关联；2、唯一外键关联

1、主键关联

映射出的关系模型与单向一样：

映射文件与单向的区别在于：需要在Card加入<one-to-one>标签，指示hibernate将关联对象User根据主键加载上来。<one-to-one>不影响存储，只影响加载

User.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">
<hibernate-mapping package="com.jialin.hibernate">

	<class name="User">
		<id name="id">
			<!--采用foreign策略，可以取得关联对象的主键  -->
			<generator class="foreign">
				<!--property代表要关联的对象 -->
				<param name="property">card</param>
			</generator>
		</id>
		<property name="name" />
		
		<one-to-one name="card" />
	</class>

</hibernate-mapping>

Card.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">
<hibernate-mapping package="com.jialin.hibernate">

	<class name="Card">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="cardNo" />
		<!--<one-to-one>不影响存储，只影响加载-->
		<one-to-one name="person" />

	</class>

</hibernate-mapping>

2、唯一外键关联

映射出的关系模型与单向一样：

映射文件：

User.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">
<hibernate-mapping package="com.jialin.hibernate">

	<class name="Person">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="name" />
		<many-to-one name="card" unique="true"></many-to-one>
	</class>

</hibernate-mapping>

Card.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">
<hibernate-mapping package="com.jialin.hibernate">

	<class name="Card">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="cardNo" />
		<!--必须指定<one-to-one>
标签中的property-ref属性为关系字段的名称-->
		<one-to-one name="person" property-ref="card"/>

	</class>

</hibernate-mapping>

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