composite-element的典型用法

composite-element的典型用法

1、情景描述

       顾客Customer下订单Order，Order里面包含很多条目Item及各条目的数量quantity信息。Customer和Order是一对多的关系；Order和Item是多对多的关系。

2、数据库结构

      orders表：{ orderId , orderName }                                                                                                                                  

      item表：{ itemId , itemName }

      order_item表：{ orderId , itemId , quantity }

3、Order.hbm.xml

<hibernate-mapping>
    <class name="com.persistent.Order" table="orders">
        <id name="id" column="orderId" unsaved-value="null">
            <generator class="increment"></generator>
        </id>
        <property name="name" column="orderName"></property>       
        <set name="perchaseItems" table="order_item" lazy="false" cascade="save-update">
            <key column="orderId"></key>
            <composite-element class="com.persistent.Perchase">
                <property name="quantity"></property>
                <many-to-one name="item" column="itemId" class="com.persistent.Item" lazy="false"></many-to-one>
            </composite-element>
        </set>
    </class>
</hibernate-mapping>

4、Item.hbm.xml

<hibernate-mapping>  
   <class name="com.persistent.Item" table="item">     
     <id name="id" column="itemId" unsaved-value="null">    
        <generator class="increment">        
        </generator>    
     </id>    
     <property name="name" column="itemName"></property>             
   </class>
</hibernate-mapping>

5、Order.java、Item.java和Perchase.java

public class Order ...{
private Long id;
private String name;
private Set purchaseItems = new HashSet();
...
}

public class Item ...{    
private Long id;
private String name;
...
}

public class Perchase ...{    
private int quantity;
private Item item;
...
}

6、测试代码

Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
List result = session.createQuery("from Order").list();    
for(int i = 0; i<result.size(); i++)...{
        Order order = (Order)result.get(i);
        System.out.println(order.getId()+"    "+order.getName());
        Set perchases = order.getPurchaseItems();
for(Iterator it = perchases.iterator(); it.hasNext();)...{
       Perchase perchase = (Perchase)it.next();
       System.out.print(perchase.getQuantity()+"    ");
       System.out.println(perchase.getItem().getId()+"  "+perchase.getItem().getName());
   }
}  
session.getTransaction().commit();