Hibernate继承映射：每个子类一张表(joined-subclass)表结构

我在前面写了关于继承映射的整个继承树对应一张表的例子，但是他存在以一定的弊端。在数据表中会产生大量的null值。

为了避免这种情况的发生。我们可以这样去做：

<joined-subclass name="Skiller" table="skiller">

<key column="emp_id"/>

<property name="skill"></property>

</joined-subclass>

<joined-subclass name="Sales" table="sales">

<key column="emp_id"/>

<property name="sell"></property>

</joined-subclass>

通过使用joined-subclass映射，对每一个子类生成一张表。

1、domain类：

package com.zhaosoft.domain;

public class Employee {

private int id;

private String name;

private Department depart;

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;

}

public Department getDepart() {

return depart;

}

public void setDepart(Department depart) {

this.depart = depart;

}

}

2、各个子类：

package com.zhaosoft.domain;

public class Sales extends Employee{

private int sell;//销售额

public int getSell() {

return sell;

}

public void setSell(int sell) {

this.sell = sell;

}

}

---------------------------------------------

package com.zhaosoft.domain;

public class Skiller extends Employee{

private String skill;

public String getSkill() {

return skill;

}

public void setSkill(String skill) {

this.skill = skill;

}

}

3、映射文件：

<?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="com.zhaosoft.domain">

<!-- 当discriminator-value值为0时，为普通员工 -->

<class name="Employee" discriminator-value="0">

<id name="id">

<!-- 表示主键为自动增长 -->

<generator class="native"/>

</id>

<property name="name" type="string"/>

<many-to-one name="depart" class="Department" column="depart_id"></many-to-one>

<joined-subclass name="Skiller" table="skiller">

<key column="emp_id"/>

<property name="skill"></property>

</joined-subclass>

<joined-subclass name="Sales" table="sales">

<key column="emp_id"/>

<property name="sell"></property>

</joined-subclass>

</class>

</hibernate-mapping>

4、测试文件：

public static void add() {

Session s = null;

Transaction t=null;

try {

s=HibernateUtil.getSession();

t = s.beginTransaction();

t.begin();

Department d = new Department();

d.setName("销售部");

Employee employee1 = new Employee();

employee1.setName("小三");

employee1.setDepart(d);

Skiller employee2 = new Skiller();

employee2.setName("李斯");

employee2.setSkill("skill");

employee2.setDepart(d);

Sales employee3 = new Sales();

employee3.setName("王五");

employee3.setSell(100);

employee3.setDepart(d);

Set<Employee> set=new HashSet<Employee>();

set.add(employee1);

set.add(employee2);

set.add(employee3);

d.setEmps(set);

s.save(d);

s.save(employee1);

s.save(employee2);

s.save(employee3);

t.commit();

} catch (Exception e) {

} finally {

if (s != null) {

s.close();

}

}

}