Hibernate采用sbuclass元素继承映射

Hibernate的继承映射可以理解两个持久化类之间的继承关系，例如来说和人之间的关系，来说继承了人，可以认为来说是一个特殊的人，如果对人进行查询，老师的实例也将被得到。各个类的代码如下：

package com.pengsuen.bean;

public class Person
{

	private long id;

	private String name;

	private char gender;

	private Address address;


	public Person()
	{
	}

	public Person(long id , String name , char gender)
	{
		this.id = id;
		this.name = name;
		this.gender = gender;
	}


	public void setId(long id)
	{
		this.id = id;
	}
	public long getId()
	{
		return this.id;
	}


	public void setName(String name)
	{
		this.name = name;
	}
	public String getName()
	{
		return this.name;
	}


	public void setGender(char gender)
	{
		this.gender = gender;
	}
	public char getGender()
	{
		return this.gender;
	}


	public void setAddress(Address address)
	{
		this.address = address;
	}
	public Address getAddress()
	{
		return this.address;
	}
}

package com.pengsuen.bean;

public class Address {
	private String detail;
	private String zip;
	private String country;
	
	public Address() {}
	
	public Address(String detail, String zip, String country) {
		this.detail = detail;
		this.zip = zip;
		this.country = country;
	}

	public String getDetail() {
		return detail;
	}

	public void setDetail(String detail) {
		this.detail = detail;
	}

	public String getZip() {
		return zip;
	}

	public void setZip(String zip) {
		this.zip = zip;
	}

	public String getCountry() {
		return country;
	}

	public void setCountry(String country) {
		this.country = country;
	}
	
	
}

package com.pengsuen.bean;

public class Customer extends Person{
	private String comments;
	private Employee employee;
	
	public Customer() {}
	
	public Customer(String comments) {
		this.comments = comments;
	}

	public String getComments() {
		return comments;
	}

	public void setComments(String comments) {
		this.comments = comments;
	}

	public Employee getEmployee() {
		return employee;
	}

	public void setEmployee(Employee employee) {
		this.employee = employee;
	}
	
}

package com.pengsuen.bean;

import java.util.HashSet;
import java.util.Set;

public class Employee extends Person{
	private String title;
	private double salary;
	private Set<Customer> customers = new HashSet<Customer>();
	private Manager manager;
	
	public Employee() {}
	
	public Employee(String title, double salary) {
		this.title = title;
		this.salary = salary;
	}

	public String getTitle() {
		return title;
	}

	public void setTitle(String title) {
		this.title = title;
	}

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public Set<Customer> getCustomers() {
		return customers;
	}

	public void setCustomers(Set<Customer> customers) {
		this.customers = customers;
	}

	public Manager getManager() {
		return manager;
	}

	public void setManager(Manager manager) {
		this.manager = manager;
	}
}

package com.pengsuen.bean;

import java.util.HashSet;
import java.util.Set;

public class Manager extends Employee{
	private String department;
	private Set<Employee> employees = new HashSet<Employee>();
	
	public Manager() {}
	
	public Manager(String department) {
		this.department = department;
	}

	public String getDepartment() {
		return department;
	}

	public void setDepartment(String department) {
		this.department = department;
	}

	public Set<Employee> getEmployees() {
		return employees;
	}

	public void setEmployees(Set<Employee> employees) {
		this.employees = employees;
	}

	
	
	
}

在这种映射策略下，整个继承树的所有实例都将保存在同一个表内，因此，需要在该表中额外增加一列，使用该列来区分每行记录到底是那个类的实例--这个列被称为辨别者列（discriminator），配置文件如下：

<?xml version="1.0" encoding="utf8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.pengsuen.bean">
	<class name="Person" discriminator-value="Person">
		<id name="id" column="person_id">
			<generator class="increment"/>
		</id>
		<discriminator column="wawa" type="string"/>
		<property name="name" length="80"/>
		<property name="gender"/>
		<component name="address">
			<property name="detail"/>
			<property name="zip"/>
			<property name="country"/>
		</component>
		<subclass name="Employee" discriminator-value="Employee">
			<property name="title" />
			<property name="salary" />
			<many-to-one name="manager" column="manager_id"/>
			<set name="customers" inverse="true">
				<key column="empoyee_id"/>
				<one-to-many class="Customer"/>
			</set>
			<subclass name="Manager" discriminator-value="Manager">
				<property name="department"/>
				<set name="employees" inverse="true">
					<key column="manager_id"/>
					<one-to-many class="Employee"/>
				</set>
			</subclass>
		</subclass>
		<subclass name="Customer" discriminator-value="Customer">
			<property name="comments"/>
			<many-to-one name="employee" column="empoyee_id"/>
		</subclass>
	</class>
</hibernate-mapping>

总配置文件hibernate.cfg.xml略

测试代码如下：

package com.pengsuen.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.pengsuen.bean.Address;
import com.pengsuen.bean.Customer;
import com.pengsuen.bean.Employee;
import com.pengsuen.bean.Manager;
import com.pengsuen.bean.Person;
public class Test {
	
	public static void main(String[] args) {
		Configuration conf = new Configuration().configure();
		SessionFactory sf = conf.buildSessionFactory(); 
		Session session = sf.openSession();
		Transaction tx = session.beginTransaction();
	
				Employee employee1 = new Employee();
				employee1.setName("Sean");
				employee1.setTitle("Coder");
				employee1.setGender('M');
				employee1.setSalary(4500);
				employee1.setAddress(new Address("NYC","123456","USA"));
				
				
				Employee employee2 = new Employee();
				employee2.setName("Peter");
				employee2.setTitle("Coder");
				employee2.setGender('M');
				employee2.setSalary(4500);
				employee2.setAddress(new Address("Beijing","123456","China"));
				
				
				
				
				Manager grace = new Manager();
				grace.setName("Grace");
				grace.setTitle("Manager");
				grace.setGender('F');
				grace.setSalary(12000);
				grace.setAddress(new Address("CA","523034","USA"));
				grace.setDepartment("Si");
				
				employee2.setManager(grace);
				
				
				
				Customer customer1 = new Customer();
				customer1.setName("Mike");
				customer1.setGender('M');
				customer1.setAddress(new Address("Beijing","233034","China"));
				customer1.setComments("kfljsdfkjasklfjkasld");
				
				customer1.setEmployee(grace);
				
				
				Person lee = new Person();
				lee.setName("Yeeku");
				lee.setGender('M');
				lee.setAddress(new Address("Beijing","434333","China"));

				session.save(lee);
				session.save(grace);
				session.persist(employee1);
				session.persist(employee2);
				session.save(customer1);
		
		tx.commit();
		session.close();
		sf.close();
	
	}
}