Hibernate one-to-one有两种形式：一是共享主键的形式进行关联，二就是独立外键的形式进行关联：
例如：人（Person）和护照（Passwort）的关系是一对一的的关系：
1）共享主键的形式：
1）主表映射文件的写法：
<class name="Person" table="t_person">
<id name="id" column="p_id">
<generator class="increment"> </generator>
</id>
<property name="name" column="p_name" type="string"> </property>
<property name="birthday" column="p_birthday" type="date"> </property>
<property name="email" column="email" type="string"> </property>
<property name="phone" column="phone" type="string"> </property>
<one-to-one name="passport" cascade="all"> </one-to-one>
</class>
2)辅表映射文件的写法：
<class name="Passport" table="t_passport">
<id name="id" column="p_id">
<generator class="foreign">
<param name="property">person </param> //person为Passport中的关系属性
</generator>
</id>
<property name="serial" column="p_serial" type="string"> </property>
<property name="expiry" column="p_expiry" type="integer"> </property>
<property name="date" column="p_date" type="date"> </property>
<one-to-one name="person" constrained="true" cascade="all">
</one-to-one>
</class>
2)独立外键的关联方式：
1）主表映射文件的写法：
<class name="Person" table="t_person">
<id name="id" column="p_id">
<generator class="increment"> </generator>
</id>
<property name="name" column="p_name" type="string"> </property>
<property name="birthday" column="p_birthday" type="date"> </property>
<property name="email" column="email" type="string"> </property>
<property name="phone" column="phone" type="string"> </property>
<one-to-one name="passport" property-ref="person" cascade="all"> </one-to-one> //person为实体类Passwort中的关系属性。
</class>
2)辅表映射文件的写法：
<class name="Passport" table="t_passport">
<id name="id" column="p_id">
<generator class="increment">
</generator>
</id>
<property name="serial" column="p_serial" type="string"> </property>
<property name="expiry" column="p_expiry" type="integer"> </property>
<property name="date" column="p_date" type="date"> </property>
<many-to-one unique="true" name="person" column="pss_id">//pss_id为外键列
</one-to-one>
</class>