组件(Component)映射
Component(组件)是一个被包含的对象,它作为值类型被持久化,而非一个被引用的实体。“component(组件)”这一术语指的是面向对象的合成概念(而并不是系统构架层次上的组件的概念)。在hibernate中可借助Component节点的定义,完成对复杂数据表的细分。在hibernate语义中,将某个实例对象中的一个逻辑组成称为Component(组件)。Component(组件)与实体对象的根本差别就在于Componet(组件)没有标识符(identity),它作为一个逻辑组成完全从属于实体对象。
还是以我第一个hibernate实例为例来说明组件映射:
User实体类如下:
package eg; public class User { private int id; private Name name;//Name是另一个类 private Date birthday; //setter和getter方法省略 }
Name类如下:
package eg; public class Name { private String firstName; private String lastName; //省略setter和getter方法 }
User.hbm.xml映射文件如下:
<?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="eg.User" > <id name="id" > <generator class="native" /> </id> <component name="name"> <property name="firstName" column="first_name" /> <property name="lastName" column="last_name" /> </component> <property name="birthday" /> </class> </hibernate-mapping
测试类如下:
public class TestUser { @Test public void test1(){ Configuration config = new Configuration(); config.configure(); SessionFactory factory = config.buildSessionFactory(); Session session = factory.openSession(); Transaction tran = session.beginTransaction(); User user = new User(); Name name = new Name(); name.setFirstName("long"); name.setLastName("xiao"); user.setName(name); user.setBirthday(new Date()); session.save(user); tran.commit(); session.close(); } }
测试程序运行后,数据库中生成了user表,创建语句如下:
DROP TABLE IF EXISTS `test`.`user`; CREATE TABLE `test`.`user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `first_name` varchar(255) DEFAULT NULL, `last_name` varchar(255) DEFAULT NULL, `birthday` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
数据库中记录如下所示:
+----+------------+-----------+----------+
| id | first_name | last_name | birthday |
+----+------------+-----------+----------+
| 1 | long | xiao | NULL |
+----+------------+-----------+----------+
1 row in set (0.00 sec)