| 人们总是在失去时，才了解到事情的本质 |
需求：动物、猫、猴子
1、简单继承映射
Animal.java
package com.rk.hibernate.n_inheritance1;
public abstract class Animal
{
private int id;
private String name;
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;
}
}Cat.java
package com.rk.hibernate.n_inheritance1;
public class Cat extends Animal
{
private String catchMouse;
public String getCatchMouse()
{
return catchMouse;
}
public void setCatchMouse(String catchMouse)
{
this.catchMouse = catchMouse;
}
@Override
public String toString()
{
return "Cat [id=" + getId() + ", name=" + getName() + ", catchMouse=" + catchMouse + "]";
}
}Cat.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.rk.hibernate.n_inheritance1" auto-import="true">
<class name="Cat" table="T_Cat">
<!-- 简单继承映射： 父类属性直接写 -->
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"></property>
<property name="catchMouse" column="catchMouse"></property>
</class>
</hibernate-mapping>App.java
package com.rk.hibernate.n_inheritance1;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App
{
private static SessionFactory sf;
static
{
sf = new Configuration()
.configure()
.addClass(Cat.class)
.buildSessionFactory();
}
@Test
public void testSave()
{
Session session = sf.openSession();
session.beginTransaction();
//猫
Cat cat = new Cat();
cat.setName("大花猫");
cat.setCatchMouse("抓小老鼠");
//保存
session.save(cat);
session.getTransaction().commit();
session.close();
}
@Test
public void testGetCat()
{
Session session = sf.openSession();
session.beginTransaction();
//通过HQL查询Cat
Query q = session.createQuery("from Cat");
List<Cat> list = q.list();
System.out.println(list);
session.getTransaction().commit();
session.close();
}
@Test
public void testGetAnimal()
{
Session session = sf.openSession();
session.beginTransaction();
// 获取时候注意：当写hql查询的使用，通过父类查询必须写上类的全名
Query q = session.createQuery("from com.rk.hibernate.n_inheritance1.Animal");
List<Cat> list = q.list();
System.out.println(list);
session.getTransaction().commit();
session.close();
}
}生成的T_Cat表
| 总结：简单继承映射，有多少个子类，写多少个映射文件！ |
2、继承映射
下面3种方法都是只使用一个映射文件（Animal.hbm.xml文件），但是不同的方法生成的数据库表的数量不同。
2.1、所有子类映射到同一张表（1张表）
什么情况用？
子类教多，且子类较为简单，即只有个别属性！
好处：因为使用一个映射文件， 减少了映射文件的个数。
缺点：（不符合数据库设计原则）
Animal.java
package com.rk.hibernate.n_inheritance2;
public abstract class Animal
{
private int id;
private String name;
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;
}
}Cat.java
package com.rk.hibernate.n_inheritance2;
public class Cat extends Animal
{
private String catchMouse;
public String getCatchMouse()
{
return catchMouse;
}
public void setCatchMouse(String catchMouse)
{
this.catchMouse = catchMouse;
}
@Override
public String toString()
{
return "Cat [id=" + getId() + ", name=" + getName() + ", catchMouse=" + catchMouse + "]";
}
}Monkey.java
package com.rk.hibernate.n_inheritance2;
public class Monkey extends Animal
{
private String eatBanana;
public String getEatBanana()
{
return eatBanana;
}
public void setEatBanana(String eatBanana)
{
this.eatBanana = eatBanana;
}
}Animal.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">
<!--
继承映射， 所有的子类都映射到一张表
-->
<hibernate-mapping package="com.rk.hibernate.n_inheritance2" auto-import="true">
<class name="Animal" table="T_Animals">
<!-- 简单继承映射： 父类属性直接写 -->
<id name="id" column="id">
<generator class="native"></generator>
</id>
<!-- 指定鉴别器字段(区分不同的子类) -->
<discriminator column="animal_Type"></discriminator>
<property name="name" column="name"></property>
<!--
子类：猫
每个子类都用subclass节点映射
注意：一定要指定鉴别器字段，否则报错！
鉴别器字段：作用是在数据库中区别每一个子类的信息， 就是一个列(column)
discriminator-value="cat"
指定鉴别器字段,即animal_Type字段的值
如果不指定，默认为当前子类的全名
-->
<subclass name="Cat" discriminator-value="cat">
<property name="catchMouse" column="catchMouse"></property>
</subclass>
<!--
子类：猴子
-->
<subclass name="Monkey" discriminator-value="monkey">
<property name="eatBanana" column="eatBanana"></property>
</subclass>
</class>
</hibernate-mapping>App.java
package com.rk.hibernate.n_inheritance2;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App
{
private static SessionFactory sf;
static
{
sf = new Configuration()
.configure()
.addClass(Animal.class)
.buildSessionFactory();
}
@Test
public void testSave()
{
Session session = sf.openSession();
session.beginTransaction();
//猫
Cat cat = new Cat();
cat.setName("大花猫");
cat.setCatchMouse("抓小老鼠");
//猴子
Monkey monkey = new Monkey();
monkey.setName("淘气猴");
monkey.setEatBanana("吃黄香蕉");
//保存
session.save(cat);
session.save(monkey);
session.getTransaction().commit();
session.close();
}
}生成的T_Animals表
| 总结：写法较为简单：所有子类用一个映射文件，且映射到一张表！但数据库设计不合理!不推荐用。 |
2.2、每个类映射一张表(3张表)
Animal.java
package com.rk.hibernate.n_inheritance3;
public abstract class Animal
{
private int id;
private String name;
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;
}
}Cat.java
package com.rk.hibernate.n_inheritance3;
public class Cat extends Animal
{
private String catchMouse;
public String getCatchMouse()
{
return catchMouse;
}
public void setCatchMouse(String catchMouse)
{
this.catchMouse = catchMouse;
}
@Override
public String toString()
{
return "Cat [id=" + getId() + ", name=" + getName() + ", catchMouse=" + catchMouse + "]";
}
}Monkey.java
package com.rk.hibernate.n_inheritance3;
public class Monkey extends Animal
{
private String eatBanana;
public String getEatBanana()
{
return eatBanana;
}
public void setEatBanana(String eatBanana)
{
this.eatBanana = eatBanana;
}
}Animal.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">
<!--
继承映射， 每个类对应一张表(父类也对应表)
-->
<hibernate-mapping package="com.rk.hibernate.n_inheritance3" auto-import="true">
<class name="Animal" table="T_Animal_Each">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"></property>
<!--
子类：猫 t_cat
key 指定_cat表的外键字段
-->
<joined-subclass name="Cat" table="T_Cat_Each">
<key column="animal_Id"></key>
<property name="catchMouse" column="catchMouse"></property>
</joined-subclass>
<!-- 子类：猴子 t_monkey -->
<joined-subclass name="Monkey" table="T_Monkey_Each">
<key column="animal_Id"></key>
<property name="eatBanana" column="eatBanana"></property>
</joined-subclass>
</class>
</hibernate-mapping>
App.java
package com.rk.hibernate.n_inheritance3;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App
{
private static SessionFactory sf;
static
{
sf = new Configuration()
.configure()
.addClass(Animal.class)
.buildSessionFactory();
}
@Test
public void testSave()
{
Session session = sf.openSession();
session.beginTransaction();
//猫
Cat cat = new Cat();
cat.setName("大花猫");
cat.setCatchMouse("抓小老鼠");
//猴子
Monkey monkey = new Monkey();
monkey.setName("淘气猴");
monkey.setEatBanana("吃黄香蕉");
//保存
session.save(cat);
session.save(monkey);
session.getTransaction().commit();
session.close();
}
}生成的T_Animal_Each表
生成的T_Cat_Each表
生成的T_Monkey_Each表
| 总结：一个映射文件，存储所有的子类； 子类父类都对应表； 缺点：表结构比较负责，插入一条子类信息，需要用2条sql： 往父类插入、往子类插入！ |
2.3、(推荐)每个子类映射一张表， 父类不对应表(2张表)
Animal.java
package com.rk.hibernate.n_inheritance4;
public abstract class Animal
{
private String id;
private String name;
public String getId()
{
return id;
}
public void setId(String id)
{
this.id = id;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
}Cat.java
package com.rk.hibernate.n_inheritance4;
public class Cat extends Animal
{
private String catchMouse;
public String getCatchMouse()
{
return catchMouse;
}
public void setCatchMouse(String catchMouse)
{
this.catchMouse = catchMouse;
}
@Override
public String toString()
{
return "Cat [id=" + getId() + ", name=" + getName() + ", catchMouse=" + catchMouse + "]";
}
}Monkey.java
package com.rk.hibernate.n_inheritance4;
public class Monkey extends Animal
{
private String eatBanana;
public String getEatBanana()
{
return eatBanana;
}
public void setEatBanana(String eatBanana)
{
this.eatBanana = eatBanana;
}
}Animal.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">
<!--
继承映射， 每个类对应一张表(父类不对应表)
-->
<hibernate-mapping package="com.rk.hibernate.n_inheritance4" auto-import="true">
<!--
abstract="true" 指定实体类对象不对应表，即在数据库内不生成表
-->
<class name="Animal" table="T_Animal_Final">
<!-- 如果用union-subclass节点，主键生成策略不能为自增长！ -->
<id name="id" column="id">
<generator class="uuid"></generator>
</id>
<property name="name" column="name"></property>
<!--
子类：猫
union-subclass
table 指定为表名, 表的主键即为id列
-->
<union-subclass name="Cat" table="T_Cat_Final">
<property name="catchMouse" column="catchMouse"></property>
</union-subclass>
<!-- 子类：猴子 -->
<union-subclass name="Monkey" table="T_Monkey_Final">
<property name="eatBanana" column="eatBanana"></property>
</union-subclass>
</class>
</hibernate-mapping>
App.java
package com.rk.hibernate.n_inheritance4;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App
{
private static SessionFactory sf;
static
{
sf = new Configuration()
.configure()
.addClass(Animal.class)
.buildSessionFactory();
}
@Test
public void testSave()
{
Session session = sf.openSession();
session.beginTransaction();
//猫
Cat cat = new Cat();
cat.setName("大花猫");
cat.setCatchMouse("抓小老鼠");
//猴子
Monkey monkey = new Monkey();
monkey.setName("淘气猴");
monkey.setEatBanana("吃黄香蕉");
//保存
session.save(cat);
session.save(monkey);
session.getTransaction().commit();
session.close();
}
}生成的T_Animal_Final表，虽然会生成这个表，但是不会存储数据
生成的T_Cat_Final表
生成的T_Monkey_Final表
| 总结：所有的子类都写到一个映射文件；父类不对应表； 每个子类对应一张表。 |
