Hibernate 继承关系映射

hibernate对类的继承关系的三种策略。以动物（Animal、Pig、Bird）为例

一、所有类的属性（字段）放入在一张表中

特点，数据库查询效率高，但粒度比较粗，会有冗余字段，配置特点是在配置文件中添加了discriminator-value标签属性。

java类
 

package test.hibernate.spring.model;  public class Animal { 	private int id; 	private String name; 	private String 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 String getSex() { 		return sex; 	} 	public void setSex(String sex) { 		this.sex = sex; 	} 	public Animal() { 		super(); 	} 	@Override 	public String toString() { 		return "Animal [id=" + id + ", name=" + name + ", sex=" + sex + "]"; 	} 	  }

package test.hibernate.spring.model;  public class Bird extends Animal { 	private int height;  	public int getHeight() { 		return height; 	}  	public void setHeight(int height) { 		this.height = height; 	}  	public Bird() { 		super(); 	}  	@Override 	public String toString() { 		return "Bird [height=" + height + "]"; 	} 	  }

package test.hibernate.spring.model;  public class Pig extends Animal { 	private int weight;  	public int getWeight() { 		return weight; 	}  	public void setWeight(int weight) { 		this.weight = weight; 	}  	public Pig() { 		super(); 	}  	@Override 	public String toString() { 		return "Pig [weight=" + weight + "]"; 	} 	 	  }

配置文件

<?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="test.hibernate.spring.model">     <class name="Animal" table="t_animal" discriminator-value="animal">         <id name="id" type="int">             <column name="id" />             <generator class="native" />         </id>         <!-- 辩别字段，必须放在id后面 -->         <discriminator column="type" type="string"></discriminator>         <property name="name" type="java.lang.String">             <column name="name" />         </property>         <property name="sex" type="java.lang.String">             <column name="sex" />         </property>       <!--  根据类插入 辩别字段中的值 -->         <subclass name="Pig" discriminator-value="pig">         <property name="weight"></property>         </subclass>         <subclass name="Bird" discriminator-value="bird">         <property name="height"></property>         </subclass>     </class> </hibernate-mapping> 

测试

package test.hibernate.spring;  import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.boot.MetadataSources; import org.hibernate.cfg.Configuration; import org.hibernate.service.ServiceRegistry; import org.junit.After; import org.junit.Before; import org.junit.Test;  import test.hibernate.spring.model.Bird; import test.hibernate.spring.model.Pig;  public class TestSession { 	SessionFactory sessionFactory = null; 	Session session=null; 	Transaction ts=null; 	@Before 	public void beforP() { 		System.out.println("begin...."); 		/* hibernate规定，所有的配置或服务，必须配置或注册到一个服务注册类中 */ 		  Configuration configuration = new Configuration().configure(); 		  ServiceRegistry sr=configuration.getStandardServiceRegistryBuilder().build(); 		/* 从注册类中获得工厂类 */ 		  sessionFactory=new MetadataSources(sr).buildMetadata().buildSessionFactory(); 		/* 通过工厂类开启Session */ 		  session=sessionFactory.openSession(); 			/* 开启事务 */ 		  ts=session.beginTransaction(); 					} 	@After 	public void endP() { 		System.out.println("end...."); 		/* 提交事务 */ 		ts.commit(); 		/* 关闭Session */ 		session.close(); 		/* 关闭工厂 */ 		sessionFactory.close(); 		} 	@Test 	public void add() { 		Pig p=new Pig(); 		p.setName("ls"); 		p.setSex("公"); 		p.setWeight(300); 		 		Bird b=new Bird(); 		b.setName("zs"); 		b.setSex("母"); 		b.setHeight(500); 		session.save(b); 		 	} }

二、每个类一张表，用joined-subclass标签来配置，java类没有变化。

配置

<?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="test.hibernate.spring.model"> 	<class name="Animal" table="t_animal"> 		<id name="id" type="int"> 			<column name="id" /> 			<generator class="native" /> 		</id> 		<property name="name" type="java.lang.String"> 			<column name="name" /> 		</property> 		<property name="sex" type="java.lang.String"> 			<column name="sex" /> 		</property> 		<!-- 子类单独有一张表 --> 		<joined-subclass name="Pig" table="t_pig"> 			<key column="p_id"></key> 			<property name="weight" type="int" column="height"></property> 		</joined-subclass> 		<joined-subclass name="Bird" table="t_bird"> 			<key column="b_id"></key> 			<property name="height" type="int" column="height"></property> 		</joined-subclass> 	</class> </hibernate-mapping> 

测试

与第一种相同