Hibernateday05继承关系subclass映射策略

2.继承关系
  O  Product //产品          Book extends Product     Car extends Product
     integer id;              String author;//作者     
     String name;
     Double price;
 
  R   create table g_product(
    p_id integer primary key,
    p_name varchar2(30),
    p_price number(5,2),
    b_author varchar2(40),//从子类扩展的字段
    p_des  varchar2(30)//一个辨别列
  )
 
  映射文件
     1.subclass映射策略：
       整个继承树的所有实例都会保存在同一张表当中，即Product和Book的数据保存在同一张表中。为了区分数据的类型，需要在表当中添加一个列，用来描述数据的类型。
       该列也称为辨别列(discriminator)
           <!-- 在父类中添加辨别列的配置:指明辨别类的列名，同时类型
           辨别列不是对象的属性，只是为了在数据库表中去分类的作用 -->
      <discriminator column="辨别列名" type="类型" ></discriminator>
    <!-- 使用sub-class映射Product的子类 Book -->
    <subclass name="Book" discriminator-value="图书">
        <property name="author" column="b_author"></property>
    </subclass>
     subclass
        优点：父表和子表保存在一张表当中，查询的时候不用子查询和多表连接，性能快
    缺点：对于子类的字段不能加入非空约束

 

1.subclass映射策略

 

 

1.O提供实体类Product.java和Book.java

package com.jsu.hb.pojo;

public class Product {
	private Integer id;
	private String name;
	private Double price;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Double getPrice() {
		return price;
	}
	public void setPrice(Double price) {
		this.price = price;
	}
	
}

 Book.java

package com.jsu.hb.pojo;

public class Book extends Product {
	private String author;

	public String getAuthor() {
		return author;
	}

	public void setAuthor(String author) {
		this.author = author;
	}
	
}

 2.R建表

create table g_product(
	p_id integer primary key,
	p_name varchar2(30),
	p_price number(5,2),
	b_author varchar2(40),
	p_des varchar2(30)
)

 3.M提供映射文件product.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 package="com.jsu.hb.pojo">
	<!-- name:所操作对象的全路径 table:该对象所对应的表名 -->
	<class name="Product" table="g_product" discriminator-value="产品">
		<id name="id" column="p_id">
			<generator class="increment"></generator>
		</id>
		<discriminator column="p_des" type="string"></discriminator>
		<!-- 普通属性的配置，非主键属性的配置 -->
		<property name="name" column="p_name"></property>
		<property name="price" column="p_price"></property>
		<subclass name="Book" discriminator-value="图书">
			<property name="author" column="b_author"></property>
		</subclass>
	</class>
</hibernate-mapping>

 4.在hibernate.cfg.xml中对映射文件进行注册

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

<hibernate-configuration>
	<session-factory> 
		<!-- show_sql:是否显示hibernate执行的SQL语句，默认为false -->
		<property name="show_sql">true</property>
		<!-- show_sql:是否显示hibernate执行格式化输出的SQL语句，默认为false -->
		<property name="format_sql">true</property>
		<!-- 配置与数据库连接的参数 -->
		<property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
		<property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:oracle</property>
		<property name="connection.username">scott</property>
		<property name="connection.password">tiger</property>
		<!-- 2.自身属性相关的配置
			dialect:方言
			hibernate根据dialect的配置进行特定数据性能方面的调优
		 -->
		<property name="dialect">org.hibernate.dialect.Oracle9iDialect</property>
 <mapping resource="com/jsu/hb/pojo/product.hbm.xml"></mapping>	
	</session-factory>
</hibernate-configuration>

 5.提供工具类HibernateUtil.java

package com.jsu.hb.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
	private static SessionFactory sf;
	private static ThreadLocal<Session> tl= new ThreadLocal<Session>();
	static{
		try{
				Configuration cfg = new Configuration();
				cfg.configure();
				sf=cfg.buildSessionFactory();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
	public static Session openSession(){
		return sf.openSession();
	}
	public static Session getCurrentSession(){
		Session session = tl.get();//先从储存的线程中查找
		if(session==null){
			session=openSession();
			tl.set(session);
			return session;
		}
		return session;
	}
}

 6.提供测试类

package com.jsu.hb.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import com.jsu.hb.pojo.Book;
import com.jsu.hb.pojo.Product;
import com.jsu.hb.util.HibernateUtil;

public class TestBookExtends {
	@Test
	public void save(){
		Product p = new Product();
		p.setName("iphone");
		p.setPrice(300.0);
		
		Book b = new Book();
		b.setName("第一次亲密接触");
		b.setPrice(38.5);
		b.setAuthor("痞子蔡");
		
		Session session = HibernateUtil.getCurrentSession();
		Transaction tx = session.getTransaction();
		tx.begin();
		//session.save(p);
		session.save(b);
		tx.commit();
	}
}