hibernate-orm/reference/zh-cn/modules/association_mapping.xml

<chapter id="associations">

    <title>关联关系映射</title>
	
    <sect1 id="assoc-intro" revision="1">
         <title>介绍</title>   
		 
        <para>
            关联关系映射通常情况是最难配置正确的。在这个部分中，我们从单向关系映射开始，然后考虑双向关系映射，由浅至深讲述一遍典型的案例。在所有的例子中，我们都使用 <literal>Person</literal>和<literal>Address</literal>。
        </para>
        
         <para>
        	我们根据映射关系是否涉及连接表以及多样性来划分关联类型。
        </para>
		
         <para>
        	在传统的数据建模中，允许为Null值的外键被认为是一种不好的实践，因此我们所有的例子中都使用不允许为Null的外键。这并不是Hibernate的要求，即使你删除掉不允许为Null的约束，Hibernate映射一样可以工作的很好。
        </para>
		
    </sect1>

    <sect1 id="assoc-unidirectional" revision="1">
         <title>单向关联（Unidirectional associations）</title>
		 
        <sect2 id="assoc-unidirectional-m21">
        <title>多对一(many to one)</title>
        
        <para>
             <emphasis>单向many-to-one关联</emphasis>是最常见的单向关联关系。
        </para>
        
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key, addressId bigint not null )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>

        <sect2 id="assoc-unidirectional-121">
        <title>一对一（one to one）</title>
        
         <para>
             <emphasis>基于外键关联的单向一对一关联</emphasis>和<emphasis>单向多对一关联</emphasis>几乎是一样的。唯一的不同就是单向一对一关联中的外键字段具有唯一性约束。
        </para>
		
       <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId" 
        unique="true"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
         <para>
            <emphasis>基于主键关联的单向一对一关联</emphasis>通常使用一个特定的id生成器。（请注意，在这个例子中我们掉换了关联的方向。）
        </para>
		
       <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
</class>

<class name="Address">
    <id name="id" column="personId">
        <generator class="foreign">
            <param name="property">person</param>
        </generator>
    </id>
    <one-to-one name="person" constrained="true"/>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table Address ( personId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>
        
        <sect2 id="assoc-unidirectional-12m">
        <title>一对多（one to many）</title>
        
        <para>
            <emphasis>基于外键关联的单向一对多关联</emphasis>是一种很少见的情况，并不推荐使用。
        </para>
        
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses">
        <key column="personId" 
            not-null="true"/>
        <one-to-many class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table Address ( addressId bigint not null primary key, personId bigint not null )
        ]]></programlisting>
        
         <para>
            我们认为对于这种关联关系最好使用连接表。
        </para>
		
        </sect2>
    
    </sect1>

    <sect1 id="assoc-unidirectional-join" revision="1">
        <title>使用连接表的单向关联（Unidirectional associations with join tables）</title>
		 
        <sect2 id="assoc-unidirectional-join-12m">
        <title>一对多(one to many)</title>
        
         <para>
            <emphasis>基于连接表的单向一对多关联</emphasis> 应该优先被采用。请注意，通过指定<literal>unique="true"</literal>，我们可以把多样性从多对多改变为一对多。
        </para>
		
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses" table="PersonAddress">
        <key column="personId"/>
        <many-to-many column="addressId"
            unique="true"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId not null, addressId bigint not null primary key )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>

        <sect2 id="assoc-unidirectional-join-m21">
        <title>多对一（many to one）</title>
        
        <para>
            <emphasis>基于连接表的单向多对一关联</emphasis>在关联关系可选的情况下应用也很普遍。
        </para>
        
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress" 
        optional="true">
        <key column="personId" unique="true"/>
        <many-to-one name="address"
            column="addressId" 
            not-null="true"/>
    </join>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null primary key, addressId bigint not null )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>

        <sect2 id="assoc-unidirectional-join-121">
        <title>一对一（one to one）</title>
        
         <para>
            <emphasis>基于连接表的单向一对一关联</emphasis>非常少见，但也是可行的。
        </para>
		
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress" 
        optional="true">
        <key column="personId" 
            unique="true"/>
        <many-to-one name="address"
            column="addressId" 
            not-null="true"
            unique="true"/>
    </join>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>

        <sect2 id="assoc-unidirectional-join-m2m">
        <title>多对多（many to many）</title>
        
         <para>
            最后，还有 <emphasis>单向多对多关联</emphasis>.
        </para>
		
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses" table="PersonAddress">
        <key column="personId"/>
        <many-to-many column="addressId"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId) )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>

    </sect1>

    <sect1 id="assoc-bidirectional" revision="1">
        <title>双向关联（Bidirectional associations）</title>
        
        <sect2 id="assoc-bidirectional-m21">
        <title>一对多（one to many) / 多对一（many to one）</title>
        
         <para>
            <emphasis>双向多对一关联</emphasis> 是最常见的关联关系。（这也是标准的父/子关联关系。）
        </para>
		
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <set name="people" inverse="true">
        <key column="addressId"/>
        <one-to-many class="Person"/>
    </set>
</class>]]></programlisting>

        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key, addressId bigint not null )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>
        
        <sect2 id="assoc-bidirectional-121">
        <title>一对一（one to one）</title>
        
         <para>
           <emphasis>基于外键关联的双向一对一关联</emphasis>也很常见。
        </para>
		
       <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address" 
        column="addressId" 
        unique="true"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
   <one-to-one name="person" 
        property-ref="address"/>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
         <para>
            <emphasis>基于主键关联的一对一关联</emphasis>需要使用特定的id生成器。
        </para>
		
       <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <one-to-one name="address"/>
</class>

<class name="Address">
    <id name="id" column="personId">
        <generator class="foreign">
            <param name="property">person</param>
        </generator>
    </id>
    <one-to-one name="person" 
        constrained="true"/>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table Address ( personId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>
        
    </sect1>

    <sect1 id="assoc-bidirectional-join" revision="1">
        <title>使用连接表的双向关联（Bidirectional associations with join tables）</title>
        
        <sect2 id="assoc-bidirectional-join-12m">
        <title>一对多（one to many） /多对一（ many to one）</title>
        
         <para>
             <emphasis>基于连接表的双向一对多关联</emphasis>。注意<literal>inverse="true"</literal>可以出现在关联的任意一端，即collection端或者join端。
        </para>
		
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses" 
        table="PersonAddress">
        <key column="personId"/>
        <many-to-many column="addressId"
            unique="true"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress" 
        inverse="true" 
        optional="true">
        <key column="addressId"/>
        <many-to-one name="person"
            column="personId"
            not-null="true"/>
    </join>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null, addressId bigint not null primary key )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>

         <sect2 id="assoc-bidirectional-join-121">
        <title>一对一（one to one）</title>
        
         <para>
            <emphasis>基于连接表的双向一对一关联</emphasis>极为罕见，但也是可行的。
        </para>
		
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress" 
        optional="true">
        <key column="personId" 
            unique="true"/>
        <many-to-one name="address"
            column="addressId" 
            not-null="true"
            unique="true"/>
    </join>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress" 
        optional="true"
        inverse="true">
        <key column="addressId" 
            unique="true"/>
        <many-to-one name="address"
            column="personId" 
            not-null="true"
            unique="true"/>
    </join>
</class>]]></programlisting>
        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>

        </sect2>
        
        <sect2 id="assoc-bidirectional-join-m2m">
        <title>多对多（many to many）</title>
        
        <para>
            最后，还有 <emphasis>双向多对多关联</emphasis>.
        </para>
        
        <programlisting><![CDATA[<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses">
        <key column="personId"/>
        <many-to-many column="addressId"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <set name="people" inverse="true">
        <key column="addressId"/>
        <many-to-many column="personId"
            class="Person"/>
    </set>
</class>]]></programlisting>

        <programlisting><![CDATA[
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId) )
create table Address ( addressId bigint not null primary key )
        ]]></programlisting>
        
        </sect2>
        
    </sect1>


</chapter>