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>

lt;/hibernate-mapping>