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();}}