Hibernate一对多单向关联映射

                   一对多关联映射（单向）

 

1、People.hbm.xml

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping 
        PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping default-lazy="false">  
   <class name="com.persistent.People" table="people">     
     <id name="id" column="peopleId" unsaved-value="0">    
        <generator class="increment">        
        </generator>    
     </id>     
     <property name="name" column="name"></property>     
     <set name="addresses">
        <key column="peopleId" not-null="true"/>
        <one-to-many class="com.persistent.Address"/>
     </set>     
   </class>
</hibernate-mapping>

 

2、address.hbm.xml

 

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping 
        PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
  <class name="com.persistent.Address" table="address">  
    <id name="id" column="addressId" unsaved-value="0">
        <generator class="increment">
        </generator>
    </id>
     <property name="peopleId" column="peopleId" 
                    insert="false" update="false">
    </property>    
    <property name="addressName" column="addressName"></property>
  </class>  
</hibernate-mapping>

 

3、测试程序

 

  

Session session = HibernateSessionFactory.getSession();
session.beginTransaction();
List result = session.createQuery("from People").list();    
session.getTransaction().commit();
for(int i = 0; i<result.size(); i++){
   People people = (People)result.get(i);
   System.out.println(people.getId()+"    "+people.getName());
   Set addresses = people.getAddresses();
   for(Iterator it = addresses.iterator(); it.hasNext();){
      Address address = (Address)it.next();
      System.out.println(address.getId()+" "
                         +address.getPeopleId()+" "
                         +address.getAddressName());
   }
}        

 

 

如果加了阴影部分,则运行结果为：

Hibernate: select people0_.peopleId as peopleId0_, people0_.name as name0_ from people people0_

Hibernate: select addresses0_.peopleId as peopleId1_, addresses0_.addressId as addressId1_, addresses0_.addressId as addressId1_0_, addresses0_.peopleId as peopleId1_0_, addresses0_.addressName as addressN3_1_0_ from address addresses0_ where addresses0_.peopleId=?

Hibernate: select addresses0_.peopleId as peopleId1_, addresses0_.addressId as addressId1_, addresses0_.addressId as addressId1_0_, addresses0_.peopleId as peopleId1_0_, addresses0_.addressName as addressN3_1_0_ from address addresses0_ where addresses0_.peopleId=?

1    lucy

2   1    Hubei Wuhan

1   1    Hunan Shaoyang

2    lily

如果不加阴影部分，则运行结果为

Hibernate: select people0_.peopleId as peopleId0_, people0_.name as name0_ from people people0_

1    lucy

Hibernate: select addresses0_.peopleId as peopleId1_, addresses0_.addressId as addressId1_, addresses0_.addressId as addressId1_0_, addresses0_.peopleId as peopleId1_0_, addresses0_.addressName as addressN3_1_0_ from address addresses0_ where addresses0_.peopleId=?

1   1    Hunan Shaoyang

2   1    Hubei Wuhan

2    lily

Hibernate: select addresses0_.peopleId as peopleId1_, addresses0_.addressId as addressId1_, addresses0_.addressId as addressId1_0_, addresses0_.peopleId as peopleId1_0_, addresses0_.addressName as addressN3_1_0_ from address addresses0_ where addresses0_.peopleId=?

默认default-lazy为true，只有当程序中访问到People的Addresses时才会从数据库中加载。设置为false后，程序在加载People时立即就把它关联的Addresses全部加载进来。

另外，只有在People端设置才有效。