Hibernate中类的继承使用subclass实现
类与表的关系：
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Employee.java
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package blog.hibernate.domain;
public class Employee {
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;
}
@Override
public String toString() {
return "Employee{" + "id=" + id + ", name=" + name + '}';
}
}*************
Sale.java
*************
package blog.hibernate.domain;
public class Sale extends Employee {
private int sell;
public int getSell() {
return sell;
}
public void setSell(int sell) {
this.sell = sell;
}
@Override
public String toString() {
return "Sale{" + "id=" + this.getId() + ", name=" + this.getName() + "sell=" + sell + '}';
}
}*************
Skill.java
*************
package blog.hibernate.domain;
public class Skill extends Employee{
private String skiller;
public String getSkiller() {
return skiller;
}
public void setSkiller(String skiller) {
this.skiller = skiller;
}
@Override
public String toString() {
return "Skill{" + "id=" + this.getId() + ", name=" + this.getName() + "skiller=" + skiller + '}';
}
}
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Employee.hbm.xml
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<?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="blog.hibernate.domain">
<class name="Employee" table="employees" discriminator-value="0">
<id name="id" column="EMPLOYEE_ID">
<generator class="native" />
</id>
<discriminator column="type" type="int" force="false" />
<property name="name" column="EMPLOYEE_NAME" />
<subclass name="Sale" discriminator-value="1">
<property name="sell" column="SELL"/>
</subclass>
<subclass name="Skill" discriminator-value="2">
<property name="skiller" column="SKILLER"/>
</subclass>
</class>
</hibernate-mapping>*******************
HibernateUtil.java
*******************
package blog.hibernate;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
public final class HibernateUtil {
private static SessionFactory sessionFactory;
private HibernateUtil(){}
static{
Configuration cfg = new Configuration();
sessionFactory = cfg.configure("hibernate.cfg.xml").buildSessionFactory();
}
public static SessionFactory getSessionFactory(){
return sessionFactory;
}
public static Session getSession(){
return sessionFactory.openSession();
}****************
hibernate.cfg.xml
***************
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">org.gjt.mm.mysql.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/extend</property><!-- ///表示连接本机的数据库//localhost:3306 -->
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">1234</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.hbm2ddl.auto">create</property>
<property name="hibernate.show_sql">true</property>
<mapping resource="blog/hibernate/domain/Employee.hbm.xml"/>
</session-factory>
</hibernate-configuration>******************
junit test: Extend.java
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package junit.test;
import java.util.logging.Logger;
import java.util.logging.Level;
import org.hibernate.Transaction;
import blog.hibernate.HibernateUtil;
import blog.hibernate.domain.Employee;
import blog.hibernate.domain.Sale;
import blog.hibernate.domain.Skill;
import org.hibernate.Session;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
public class Extend {
public Extend() {
}
@BeforeClass
public static void setUpClass() throws Exception {
}
@AfterClass
public static void tearDownClass() throws Exception {
}
@Before
public void setUp() {
}
@Test
public void test() {
add();
query();
}
public void add() {
Employee emp1 = new Employee();
emp1.setName("lisi");
Skill emp2 = new Skill();
emp2.setName("wangwu");
emp2.setSkiller("java");
Sale emp3 = new Sale();
emp3.setName("sunliu");
emp3.setSell(300000);
Session session = null;
Transaction tx = null;
try {
session = HibernateUtil.getSession();
tx = session.beginTransaction();
session.save(emp3);
session.save(emp2);
session.save(emp1);
tx.commit();
} catch (Exception e) {
Logger.getLogger(Extend.class.getName()).log(Level.SEVERE, null, e);
if (tx != null) {
tx.rollback();
}
} finally {
if (session != null) {
session.close();
}
}
}
public void query() {
Session session = null;
try {
session = HibernateUtil.getSession();
Employee emp1 = (Employee) session.get(Sale.class, 1);
Employee emp2 = (Employee) session.get(Skill.class, 2);
Employee emp3 = (Employee) session.get(Employee.class, 3);
System.out.println(emp1.toString());
System.out.println(emp2.toString());
System.out.println(emp3.toString());
} catch (Exception e) {
Logger.getLogger(Extend.class.getName()).log(Level.SEVERE, null, e);
} finally {
if (session != null) {
session.close();
}
}
}
}
用subclass只会生成一张表，表的结构为：
CREATE TABLE `employees` (
`EMPLOYEE_ID` int(11) NOT NULL auto_increment,
`type` int(11) NOT NULL,
`EMPLOYEE_NAME` varchar(255) collate utf8_unicode_ci default NULL,
`SELL` int(11) default NULL,
`SKILLER` varchar(255) collate utf8_unicode_ci default NULL,
PRIMARY KEY (`EMPLOYEE_ID`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
employees
Hibernate生成的sql语句为：
Hibernate: insert into employees (EMPLOYEE_NAME, SELL, type) values (?, ?, 1)
Hibernate: insert into employees (EMPLOYEE_NAME, SKILLER, type) values (?, ?, 2)
Hibernate: insert into employees (EMPLOYEE_NAME, type) values (?, 0)
Hibernate:
select
sale0_.EMPLOYEE_ID as EMPLOYEE1_0_0_,
sale0_.EMPLOYEE_NAME as EMPLOYEE3_0_0_,
sale0_.SELL as SELL0_0_
from
employees sale0_
where
sale0_.EMPLOYEE_ID=? and sale0_.type=1
Hibernate:
select
skill0_.EMPLOYEE_ID as EMPLOYEE1_0_0_,
skill0_.EMPLOYEE_NAME as EMPLOYEE3_0_0_,
skill0_.SKILLER as SKILLER0_0_
from
employees skill0_
where
skill0_.EMPLOYEE_ID=? and skill0_.type=2
Hibernate:
select
employee0_.EMPLOYEE_ID as EMPLOYEE1_0_0_,
employee0_.EMPLOYEE_NAME as EMPLOYEE3_0_0_,
employee0_.SELL as SELL0_0_,
employee0_.SKILLER as SKILLER0_0_,
employee0_.type as type0_0_
from
employees employee0_
where
employee0_.EMPLOYEE_ID=?
测试结果为：
Sale{id=1, name=sunliusell=300000}
Skill{id=2, name=wangwuskiller=java}
Employee{id=3, name=lisi}
PS:
采用这种方式的好处是数据处理的效率高；缺点是数据库的表结构不符合关系模型的设计理念，而且子类对应的字段不能强制为非空，如果要新增一个子类那么就必须更改表的结构即新增一列。
