淺析Hibernate映射（二）——關係映射（3）

雙向一對一關聯映射

 

與單向一對一關聯映射同樣，雙向映射依然能夠採用兩種方式實現：一、主鍵關聯；二、惟一外鍵關聯

 

一、主鍵關聯

映射出的關係模型與單向同樣：

映射文件與單向的區別在於：須要在Card加入<one-to-one>標籤，指示hibernate將關聯對象User根據主鍵加載上來。<one-to-one>不影響存儲，隻影響加載

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">
            <!--採用foreign策略，能夠取得關聯對象的主鍵  -->
            <generator class="foreign">
                <!--property表明要關聯的對象 -->
                <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>不影響存儲，隻影響加載-->
        <one-to-one name="person" />

    </class>

</hibernate-mapping>

二、惟一外鍵關聯

映射出的關係模型與單向同樣：

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" />
        <!--必須指定<one-to-one>
標籤中的property-ref屬性爲關係字段的名稱-->
        <one-to-one name="person" property-ref="card"/>

</class>

lt;/hibernate-mapping>