Hibernate（15）_继承映射

本系列博客汇总在这里：Hibernate 汇总

继承映射

• 一、单表继承映射
• 二、父子表继承映射
• 三、子表继承映射

---

源码工程文件为：hibernate4.3_11

一、单表继承映射

1、配置

<?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">
<!-- 
package：指定当前映射文件的实体类model所在的包
 -->
<hibernate-mapping package="com.wyx.hiber.model">
	
	<class name="Animal" table="t_animal">
		<!-- id
			是主键映射配置
		 -->
		<id name="anId" column="an_id">
			<!-- 
				generator：主键的映射策略
			 -->
			<generator class="native"></generator>
		</id>
		<!-- 鉴别器，在单表中加入一列来区分子类的 -->
		<discriminator column="type" type="string"></discriminator>
		<property name="anName" column="an_name"></property>
		<property name="gender"></property>
		
		<!-- 子类配置 
			name:子类的类名
			discriminator-value：区分子类的值
		-->
		<subclass name="Pig" discriminator-value="p">
			<!-- 子类中的属性映射 -->
			<property name="weight"></property>
		</subclass>
		<subclass name="Bird" discriminator-value="b">
			<property name="height"></property>
		</subclass>
	</class>
</hibernate-mapping>

2、保存

public void save()
{
	Session session = HibernateUtils.getSession();
	Transaction tx = session.beginTransaction();

	try
	{
		Pig pig = new Pig();
		pig.setAnName("天蓬元帅");
		pig.setGender(1);
		pig.setWeight(200);

		session.save(pig);

		Bird b = new Bird();
		b.setAnName("大鹏");
		b.setGender(1);
		b.setHeight(10000);
		session.save(b);
		tx.commit();
	} catch (Exception e)
	{
		e.printStackTrace();
		tx.rollback();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

3、子类查询

public void query()
{
	Session session = HibernateUtils.getSession();

	try
	{
		Pig pig = (Pig) session.load(Pig.class, 1);
		System.out.println(pig.getAnName() + "    " + pig.getWeight());
	} catch (Exception e)
	{
		e.printStackTrace();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

4、父类查询

/**
* load的延迟加载的方式返回的是代理类，所以无法做多态查询
 */
@Test
public void query1()
{
	Session session = HibernateUtils.getSession();
	try
	{
		Animal animal = (Animal) session.load(Animal.class, 1);
		if (animal instanceof Pig)
		{
			System.out.println("是猪");
		} else
		{
			System.out.println("不是猪");
		}
	} catch (Exception e)
	{
		e.printStackTrace();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

/**
* get支持多态查询
 */
@Test
public void query2()
{
	Session session = HibernateUtils.getSession();
	try
	{
		Animal animal = (Animal) session.get(Animal.class, 1);
		if (animal instanceof Pig)
		{
			System.out.println("是猪");
			Pig pig = (Pig) animal;
			System.out.println(pig.getAnName() + "   " + pig.getWeight());
		} else
		{
			System.out.println("不是猪");
		}
	} catch (Exception e)
	{
		e.printStackTrace();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

二、父子表继承映射

配置

<?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">
<!-- 
package：指定当前映射文件的实体类model所在的包
 -->
<hibernate-mapping package="com.wyx.hiber.model">
	
	<class name="Animal" table="t_animal" >
		<!-- id
			是主键映射配置
		 -->
		<id name="anId" column="an_id">
			<!-- 
				generator：主键的映射策略
			 -->
			<generator class="native"></generator>
		</id>
		
		<property name="anName" column="an_name"></property>
		<property name="gender"></property>
		<!-- 
			子类映射配置
			name：子类的名字
			table：子类映射表名
		 -->
		<joined-subclass name="Pig" table="t_pig">
			<!-- 
				key:字表的主键设置
				column：主键名称
			 -->
			<key column="pid"></key>
			<!-- 子类的属性映射 -->
			<property name="weight"></property>
		</joined-subclass>
		<joined-subclass name="Bird" table="t_bird">
			<!-- 
				key:字表的主键设置
				column：主键名称
			 -->
			<key column="bid"></key>
			<!-- 子类的属性映射 -->
			<property name="height"></property>
		</joined-subclass>
		
	</class>
</hibernate-mapping>

父子表继承映射，父类产生父类的表，子类产生子类的表。

父子表的映射因为生成的表多张，查询的时候我们需要多表连接查询，所以效率没有单表继承映射高。

三、子表继承映射

配置

<?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">
<!-- 
package：指定当前映射文件的实体类model所在的包
 -->
<hibernate-mapping package="com.wyx.hiber.model">
	
	<!-- 字表映射，需要把父类的映射设置成抽象的（不会产生父表）
		abstract="true"
	 -->
	<class name="Animal" table="t_animal" abstract="true">
		<!-- id
			是主键映射配置
		 -->
		<id name="anId" column="an_id">
			<!-- 
				generator：主键的映射策略
			 -->
			<generator class="uuid"></generator>
		</id>
		
		<property name="anName" column="an_name"></property>
		<property name="gender"></property>
		
		<!-- 子表映射 -->
		<union-subclass name="Pig" table="t_pig">
			<property name="weight"></property>
		</union-subclass>
		<union-subclass name="Bird" table="t_bird">
			<property name="height"></property>
		</union-subclass>
	</class>
</hibernate-mapping>

导出表后，产生两张子表，字表中包含父类的映射字段，存取方式一样不再复述。

如有错误，欢迎指正！