hibernate将每个类映射成表的继承

前面的一种方式是3个类放在一个表中，这样看上去不符合关系模型，但是效率快。所以就少第二种更加符合关系模型的方法。那就是将每一个类映射到每一个表。这样使表结构更加清晰。但是执行效率会比较低。

 

我还是写原来那个例子。

1.      基类

package com.fish.testdao;

 

public class Employee {

private Integerid;

private Stringname;

private Departmentdepartment;

public Integer getId() {

    return id;

}

public void setId(Integer id) {

    this.id = id;

}

public String getName() {

    return name;

}

public void setName(String name) {

    this.name = name;

}

public Department getDepartment() {

    return department;

}

public void setDepartment(Department department) {

    this.department = department;

}

 

}

2.销售类

package com.fish.testdao;

 

public class Saleextends Employee{

private float money;

 

public float getMoney() {

    return money;

}

 

public void setMoney(float money) {

    this.money = money;

}

 

}

2.      技术工类

package com.fish.testdao;

 

public class Skill extends Employee{

private Stringkiller;

 

public String getKiller() {

    return killer;

}

 

public void setKiller(String killer) {

    this.killer = killer;

}

 

}

然后写一个xml

<?xmlversion="1.0"encoding="UTF-8"?>

<!DOCTYPEhibernate-mapping PUBLIC

    "-//Hibernate/HibernateMapping DTD 3.0//EN"

    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 

<hibernate-mapping>

    <classname="com.fish.testdao.Employee"discriminator-value="0">

 

       <idname="id" column="id"type="integer">

           <generatorclass="increment"></generator>

       </id>

 

       <propertyname="name"></property>

 

       <many-to-onename="department"></many-to-one>

 

       <joined-subclassname="com.fish.testdao.Sale"table="sale">

           <keycolumn="emp_id"></key>

           <propertyname="money"></property>

       </joined-subclass>

       <joined-subclassname="com.fish.testdao.Skill"table="skill">

           <keycolumn="emp_id"></key>

           <propertyname="killer"></property>

       </joined-subclass>

   

    </class>

</hibernate-mapping>

joined-subclass这个就是可以将该类映射到另外一个表中，然后利用key和原来employee表的id相关联。这样2张表就建立了联系。

 

下面写一个测试类

package com.fish.domain;

 

import java.util.List;

 

import org.hibernate.Query;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

 

import com.fish.testdao.Department;

import com.fish.testdao.Skill;

 

public class Test6 {

    // 写一个得到session的模板

    public static Session getMySession() {

       Configuration configuration = new Configuration();

       configuration.configure("hibernate.cfg.xml");

       SessionFactory factory = configuration.buildSessionFactory();

       Session session = factory.openSession();

       return session;

    }

 

    public static void add() {

       Session session = getMySession();

       Department department = new Department();

       department.setName("财务部");

       Skill skill = new Skill();

       skill.setDepartment(department);

       skill.setKiller("技工");

       skill.setName("妮妮");

       Transaction transaction = session.beginTransaction();

       transaction.begin();

 

       session.save(department);

       session.save(skill);

       transaction.commit();

       session.close();

    }

 

    public static void query() {

       String hql = "fromSkill";

       Session session = getMySession();

       Query query = session.createQuery(hql);

       List<Skill> list = query.list();

       for (Skill i : list) {

           System.out.println(i.getName()+"是"+i.getKiller());

       }

 

    }

 

    public static void main(String[] args) {

       // add();

       query();

    }

}

我们看看数据库中的存储结果。