基本O/R映射（二）--Hibernate快速参考

composite-id
<composite-id
        name="propertyName"
        class="ClassName"
        mapped="true|false"
        access="field|property|ClassName">
        node="element-name|."

        <key-property name="propertyName" type="typename" column="column_name"/>
        <key-many-to-one name="propertyName class="ClassName" column="column_name"/>
        ......
</composite-id>
For a table with a composite key, you may map multiple properties of the class as identifier properties. The <composite-id> element accepts <key-property> property mappings and <key-many-to-one> mappings as child elements.

<composite-id>
        <key-property name="medicareNumber"/>
        <key-property name="dependent"/>
</composite-id>
Your persistent class must override equals() and hashCode() to implement composite identifier equality. It must also implements Serializable.

例如：(  孙卫琴　＜精通Hibernate:Java对象持久化技术详解＞　137页

一、定义复合属性

Customer表没有定义ID代理主键，而是以NAME字段和COMPANY＿ID作为复合主键，那么相应地，在Customer类中也不必定义id属性，而是以name和company_id作为OID,映射代码如下：

   <composite-id>
        <key-property name="name" column="NAME" type-"string"/>
        <key-property name="companyId" column-"COMPANY_ID" type="long"/>
</composite-id>

<version name-"version" column-"VERSIONI" unsaved-value="0"/>

创建：

　　Customer customer=new Customer();
       customer.setName("Tom");
       customer.setCompanyId(11);
       session.saveOrUpdate(customer);//由于customer对象的version属性为0，因此调用save()方法

加载：

　　Customer customer-=ew Customer();
       customer.setName("TOm");
       customer.setCompanyId(11);
       session.load(Customer.class,customer);

注：需要实现java.io.Serializable接口

二、定义主键类

映射复合主键的另一种方法是先定义主键类，以包含name,companyId字段，实现Serializable接口，添加映射代码如下：

　　<class name="mypack.Customer" table="CUSTOMERS">
                   <composite-id name="custoerId" class="mypack.CustomerId">
                         <key-property name="name" column="NAME" type=String/>
                         <key-property name-"companyId" column="COMPANY_ID" type="long"/>
                    </composite-id>
                   <version name="version" column="VERSION" unsaved-value="0"/>

        </class>

创建：

　　CustomerId customerId=new CustomerId("Tom",11);
       Customer customer=new Customer();
       customer.setCustomerId(customerId);
       session.saveOrUpdate(customer);

加载：

　　CustomerId customerId=new CustomerId("Tom",11);
       Customer customer=(Customer)session.load(Customer.class,customerId);

三、外键参照

　　当COMPANY_ID还作为外键参照COMPANY表，则在Customer类中：

　　　　private CustomerId customerId;
              private Company company;

        映射代码：

　　　<class name="mypack.Customer" table="CUSTOMERS">
                   <composite-id name=customerId" class ="mypack.CustomerId">
                            <key-property name="name" column="NAME" type="string"/>
                            <key-property name="companyId" column="COMPANY_ID" type="long"/>
                  </composite-id>
                  <version name="version" column="VERSION" unsaved-value="0"/>
                  <many-to-one name="company" class="mypack.Company" column="COMPANY_ID"
                                 insert="false" update="fase"/>
　　　　　<!--保存或更新Customer对象时，会忽略company属性-->
            </class>

　　也可用<key-many-to-one>映射

　　<class name="mypack.Customer" table="CUSTOMERS">
                   <composite-id name=customerId" class ="mypack.CustomerId">
                            <key-property name="name" column="NAME" type="string"/>
　　　　　　　　<key-many-to-one name="company"
                                                         class="mypack.Company"
                                                        column="COMPANY_ID"/>
　　                  <version name="version" column="VERSION" unsaved-value="0"/>

        </class>

四、Column属性

<column
        name="column_name"
        length="N"
        precision="N"
        scale="N"
        not-null="true|false"
        unique="true|false"
        unique-key="multicolumn_unique_key_name"
        index="index_name"
        sql-type="sql_type_name"
        check="SQL expression"
        default="SQL expression"/>
<formula>SQL expression</formula>
column and formula attributes may even be combined within the same property or association mapping to express, for example, exotic join conditions.

<many-to-one name="homeAddress" class="Address"
        insert="false" update="false">
    <column name="person_id" not-null="true" length="10"/>
    <formula>'MAILING'</formula>
</many-to-one>