hibernate学习10之component（组件）映射

在hibernate中,component是某个实体的逻辑组成部分，它与实体的根本区别是没有oid，
component可以成为是值对象（DDD）

采用component映射的好处：它实现了对象模型的细粒度划分，层次会更分明，复用率会更高

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
		<property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_component_mapping</property>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">bjsxt</property>
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
		<property name="hibernate.show_sql">true</property>
		
		<mapping resource="com/bjsxt/hibernate/User.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

public class User {	
	private int id;	
	private String name;
	private Contact contact; 
	//setter，getter
}
public class Contact {
	private String email;
	private String address;
	private String zipCode;
	private String contactTel;
	//setter，getter
}

利用下面的配置就可以实现组件映射，它可以增加代码复用率，假定现在还有一个类也有email，address，zipCode，contactTel这些属性，那就可以使用Contact 类来减少setter&getter，实现代码复用。
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>
	<class name="com.bjsxt.hibernate.User" table="t_user">
		<id name="id">
			<generator class="native"/>
		</id>
		<property name="name"/>
		<component name="contact">
			<property name="email"/>
			<property name="address"/>
			<property name="zipCode"/>
			<property name="contactTel"/>
		</component>
	</class>
</hibernate-mapping>

测试一下：

import org.hibernate.Session;

import junit.framework.TestCase;

public class ComponentMappingTest extends TestCase {

	public void testSave1() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			
			User user = new User();
			user.setName("张三");
			
			Contact contact = new Contact();
			contact.setAddress("xxxxx");
			contact.setEmail("[e-mail]");
			contact.setZipCode("1111111");
			contact.setContactTel("9999999999");
			
			user.setContact(contact);
			
			session.save(user);
			session.getTransaction().commit();
		}catch(Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		}finally {
			HibernateUtils.closeSession(session);
		}
	}		
}