一,概述

1)一個類中包含另一個類(車與輪子),這兩個類就是組合關係.

2)類組合關係的對映,也稱為元件對映.

3)元件類和被包含的元件類,共同對映到同一張表.

4)需求:車與輪子.

二,JavaBean設計

1)Car.java

package com.bighuan.d_component;

public class Car {

	private int id;
	private String name;
	// 車輪
	private Wheel wheel;
	
	public Car(){
		
	}

	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Wheel getWheel() {
		return wheel;
	}
	public void setWheel(Wheel wheel) {
		this.wheel = wheel;
	}
	
}
 

2)Wheel.java

package com.bighuan.d_component;
// 輪子
public class Wheel {

	private int count;
	private int size;
	
	public Wheel(){
	}
	public int getCount() {
		return count;
	}
	public void setCount(int count) {
		this.count = count;
	}
	public int getSize() {
		return size;
	}
	public void setSize(int size) {
		this.size = size;
	}
	
}
 

三,對映檔案

1)Car.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<!-- 
	元件對映
 -->
<hibernate-mapping package="com.bighuan.d_component">
	
	<class name="Car" table="t_car">
		<id name="id">
			<generator class="native"></generator>
		</id>	
		<property name="name" length="20"></property>
		
		<!-- 元件對映 -->
		<component name="wheel">
			<property name="size"></property>
			<property name="count"></property>
		</component>
		
					 
	</class>
	

</hibernate-mapping>
 

2)測試

package com.bighuan.d_component;

import org.hibernate.Hibernate;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.classic.Session;
import org.junit.Test;

public class App {
	
	private static SessionFactory sf;
	static {
		sf = new Configuration()
			.configure()
			.addClass(Car.class)   
			.buildSessionFactory();
	}

	@Test
	public void testSave() {
		
		Session session = sf.openSession();
		session.beginTransaction();
		
		// 輪子
		Wheel wheel = new Wheel();
		wheel.setSize(38);
		wheel.setCount(4);
		// 車
		Car car = new Car();
		car.setName("BMW");
		car.setWheel(wheel);
		
		// 儲存
		session.save(car);
		
		session.getTransaction().commit();
		session.close();
		
	}
	
}