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>
下篇继续
