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继承映射: 类有继承的概念, 表是没有继承的概念的, 但是可以体现这种关系

首先, 新建三个类, 分别是Animal类/Pig类/Bird类, 它们之间的关系是Pig类继承Animal类/Bird类继承Animal类, 然后建立映射关系

工程结构如图:

①单表继承映射(缺点: 出现冗余字段)

将这些属性存储在一张表中:

anId	anName	gender	weight	height	type
1	八戒	1	300		P
2	大鹏	1		10000	B

添加:

"Animal.hbm.xml"配置文件:

生成数据库表(1张表):

插入数据:

测试代码:

package com.rl.hiber.test;import org.hibernate.Session;import org.hibernate.Transaction;import org.junit.Test;import com.rl.hiber.model.Bird;import com.rl.hiber.model.Pig;import com.rl.hiber.utils.HibernateUtil;public class TestHibernate {    @Test    public void test1(){                Session session = HibernateUtil.getSessoion();        Transaction tx = session.beginTransaction();                try {            Pig pig = new Pig();            pig.setAnName("天蓬元帅");            pig.setGender(1);            pig.setWeight(300);            session.save(pig);                        Bird bird = new Bird();            bird.setAnName("大鹏");            bird.setGender(1);            bird.setHeight(10000);            session.save(bird);                        tx.commit();        } catch (Exception e) {            e.printStackTrace();            tx.rollback();        }finally{            HibernateUtil.closeResource(session);        }    }}

控制台输出:

Hibernate: insert into t_animal (an_name, gender, weight, type) values (?, ?, ?, 'p')Hibernate: insert into t_animal (an_name, gender, height, type) values (?, ?, ?, 'b')

数据库结果:

查询:

查询子类:

测试代码:

@Test    public void test2(){                Session session = HibernateUtil.getSessoion();                try {            Pig pig = (Pig) session.load(Pig.class, 1);            System.out.println(pig.getAnName()+"    "+pig.getWeight());        } catch (Exception e) {            e.printStackTrace();        }finally{            HibernateUtil.closeResource(session);        }    }

控制台输出:

Hibernate: select pig0_.an_id as an_id1_0_0_, pig0_.an_name as an_name3_0_0_, pig0_.gender as gender4_0_0_, pig0_.weight as weight5_0_0_ from t_animal pig0_ where pig0_.an_id=? and pig0_.type='p'天蓬元帅    300

查询父类:

测试代码:

/**     * load的延迟加载返回的是代理类, 所以无法完成多态(父类)查询     */    @Test    public void test3(){                Session session = HibernateUtil.getSessoion();                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{            HibernateUtil.closeResource(session);        }    }        /**     * get是急加载方式, 所以能够知道是Pig类型, 直接可以强转输出     */    @Test    public void test4(){                Session session = HibernateUtil.getSessoion();                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{            HibernateUtil.closeResource(session);        }    }

get方式的控制台输出:

Hibernate: select animal0_.an_id as an_id1_0_0_, animal0_.an_name as an_name3_0_0_, animal0_.gender as gender4_0_0_, animal0_.weight as weight5_0_0_, animal0_.height as height6_0_0_, animal0_.type as type2_0_0_ from t_animal animal0_ where animal0_.an_id=?是猪天蓬元帅    300

②父子表继承映射(无冗余字段, 但效率比①较低)

顾名思义: 父类和子类各自一张表(父类产生父类的表, 子类产生子类的表)

"Animal1.hbm.xml"配置文件:

生成数据库表(3张表):

插入数据:

测试代码不变:

@Test    public void test1(){                Session session = HibernateUtil.getSessoion();        Transaction tx = session.beginTransaction();                try {            Pig pig = new Pig();            pig.setAnName("天蓬元帅");            pig.setGender(1);            pig.setWeight(300);            session.save(pig);                        Bird bird = new Bird();            bird.setAnName("大鹏");            bird.setGender(1);            bird.setHeight(10000);            session.save(bird);                        tx.commit();        } catch (Exception e) {            e.printStackTrace();            tx.rollback();        }finally{            HibernateUtil.closeResource(session);        }    }

控制台输出:

Hibernate: insert into t_animal (an_name, gender) values (?, ?)Hibernate: insert into t_pig (weight, pid) values (?, ?)Hibernate: insert into t_animal (an_name, gender) values (?, ?)Hibernate: insert into t_bird (height, bid) values (?, ?)

数据库结果:

查询:

查询的方式跟①相同, 但是由于父子表的映射生成的表有多张, 所以查询时需要多张表连接查询, 效率较①低

Hibernate: select pig0_.pid as an_id1_0_0_, pig0_1_.an_name as an_name2_0_0_, pig0_1_.gender as gender3_0_0_, pig0_.weight as weight2_2_0_ from t_pig pig0_ inner join t_animal pig0_1_ on pig0_.pid=pig0_1_.an_id where pig0_.pid=?

Hibernate: select animal0_.an_id as an_id1_0_0_, animal0_.an_name as an_name2_0_0_, animal0_.gender as gender3_0_0_, animal0_1_.weight as weight2_2_0_, animal0_2_.height as height2_1_0_, case when animal0_1_.pid is not null then 1 when animal0_2_.bid is not null then 2 when animal0_.an_id is not null then 0 end as clazz_0_ from t_animal animal0_ left outer join t_pig animal0_1_ on animal0_.an_id=animal0_1_.pid left outer join t_bird animal0_2_ on animal0_.an_id=animal0_2_.bid where animal0_.an_id=?是猪天蓬元帅    300

③子表继承映射

"Animal2.hbm.xml"配置文件:

注意: Animal类也需要将anId改为String类型

数据表生成:

插入数据:

测试代码:

跟①相同

控制台输出结果:

Hibernate: insert into t_pig (an_name, gender, weight, an_id) values (?, ?, ?, ?)Hibernate: insert into t_bird (an_name, gender, height, an_id) values (?, ?, ?, ?)

数据库结果:

查询:

跟①相同