Hibernate 繼承映射關係 —— 類繼承樹映射成一張表

前面幾篇博客介紹了Hibernate的級聯，映射關係等，該篇介紹hibernate類繼承樹映射爲一張表，還是舉例說明

首先創建一個實體繼承樹，實體的繼承關係如圖所示：

Pig對象和Bird對象都繼承Animal，確定繼承關係之後，可以將3個類映射到一張表tb_animal中，可通過字段type用來區分不同的實體對象信息

Animal對象類：

package com.hiberbate.manytomany;
public class Animal {
	private int id;
	private String name;
	private boolean sex;
	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 boolean getSex(){
		return sex;
	}
	public void setSex(boolean sex){
		this.sex = sex;
	}

}

Pig對象類：

package com.hiberbate.manytomany;
public class Pig extends Animal{
	private int weight;	
	public int getWeight(){
		return weight;
	}
	public void setWeight(int weight){
		this.weight = weight;
	}
}

Bird對象類：

package com.hiberbate.manytomany;
public class Bird extends Animal{
	private int height;	
	public int getHeight(){
		return height;
	}
	public void setHeight(int height){
		this.height = height;
	}

}

映射文件tb_annimal.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    
<hibernate-mapping package="com.hiberbate.manytomany">
    <class name="Animal" table="tb_animal">
        <id name="id" column="id" type="int" >
            <!-- 主鍵生成策略 -->
            <generator class="assigned" />  
        </id>
        <discriminator column="type" type="string"></discriminator>
        <property name="name" type="string">
            <column name="name"/>
        </property>
        <property name="sex" type="boolean" column="sex"></property>
		
        <subclass name="Bird" discriminator-value="B">
            <property name="height"></property>             
        </subclass>
        <subclass name="Pig" discriminator-value="P">
            <property name="weight"></property>             
        </subclass>		
    </class>
</hibernate-mapping>

創建tb_animal表如圖所示：

下面做測試：

private static void classextentsTree() {
		 Session session = null;
		 Pig pig=new Pig();
		 pig.setId(5);
		 pig.setName("小豬");
		 pig.setSex(true);
		 pig.setWeight(200);

		 Bird bird=new Bird();
		 bird.setId(3);
		 bird.setName("小鳥");
		 bird.setSex(false);
		 bird.setHeight(100);

		 Animal animal=new Animal();
		 animal.setId(100);
		 animal.setName("小動物");
		 animal.setSex(false);		 
		 try {
  	        
  			session = HibernateUtil.getSession();
  			//添加數據
  			session.beginTransaction();
  			session.save(pig);
  			session.save(bird);
  	  		session.save(animal);
  			session.getTransaction().commit();
  			 
		 } catch (Exception e) {
			session.getTransaction().rollback();
			System.out.print("數據庫添加失敗");
			e.printStackTrace();
		 }finally{
			HibernateUtil.closeSession();
		 }		
	}

結果如圖：