Hibernate组件（Component）映射

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：

Java代码

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
}

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：

Java代码

package eg;
public class Name {
private String firstName;
private String lastName;
//省略setter和getter方法
}

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代码

<?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

<?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：

Java代码

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();
}
}

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：

Sql代码

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;

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：

Hibernate组件（Component）映射

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