Hibernate One-to-Many Mappings 一对多关系映射
Hibernate One-to-Many Mappings 一对多关系映射
关键点：一对多关系使用 Set 实现，
例子：一个员工可以有多个学证书。
Hibernate框架的使用步骤：
1、创建Hibernate的配置文件（hibernate.cfg.xml）
2、创建持久化类，即其实例需要保存到数据库中的类（Employee.java）
3、创建对象-关系映射文件（Employee.hbm.xml）
4、通过Hibernate API编写访问数据库的代码
创建Hibernate的配置文件（hibernate.cfg.xml）
org.hibernate.dialect.MySQLDialect
com.mysql.jdbc.Driver
jdbc:mysql://localhost/testOne2Many
root
root
true
Employee.java文件：
package com.jiangge.hblearn;
import java.util.Set;
public class Employee
{
private int id;
private String firstName;
private String lastName;
private int salary;
private Set certificates;
public Employee()
{
}
public Employee(String fname, String lname, int salary)
{
this.firstName = fname;
this.lastName = lname;
this.salary = salary;
}
public int getId()
{
return id;
}
public void setId(int id)
{
this.id = id;
}
public String getFirstName()
{
return firstName;
}
public void setFirstName(String first_name)
{
this.firstName = first_name;
}
public String getLastName()
{
return lastName;
}
public void setLastName(String last_name)
{
this.lastName = last_name;
}
public int getSalary()
{
return salary;
}
public void setSalary(int salary)
{
this.salary = salary;
}
public Set getCertificates()
{
return certificates;
}
public void setCertificates(Set certificates)
{
this.certificates = certificates;
}
}package com.jiangge.hblearn;
public class Certificate
{
private int id;
private String name;
public Certificate()
{
}
public Certificate(String name)
{
this.name = 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;
}
public boolean equals(Object obj)
{
if (obj == null)
return false;
if (!this.getClass().equals(obj.getClass()))
return false;
Certificate obj2 = (Certificate) obj;
if ((this.id == obj2.getId()) && (this.name.equals(obj2.getName())))
{
return true;
}
return false;
}
public int hashCode()
{
int tmp = 0;
tmp = (id + name).hashCode();
return tmp;
}
}创建MySQL数据库对应的表：
mysql> create table EMPLOYEE (
id INT NOT NULL auto_increment,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary INT default NULL,
PRIMARY KEY (id)
);
Query OK, 0 rows affected
mysql> create table CERTIFICATE (
id INT NOT NULL auto_increment,
certificate_name VARCHAR(30) default NULL,
employee_id INT default NULL,
PRIMARY KEY (id)
);
Query OK, 0 rows affected
mysql> 创建对象-关系映射文件（Empoyee.hbm.xml）
This class contains the employee detail.
This class contains the certificate records.
通过Hibernate API编写访问数据库的代码
package test;
import java.util.*;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import com.jiangge.hblearn.Certificate;
import com.jiangge.hblearn.Employee;
/**
* 测试类：一对多关系。一个员工可以有多个文凭证书
* CRUD操作
* @author jiangge
*
*/
public class ManageEmployee
{
private static SessionFactory factory;
public static void main(String[] args)
{
try
{
factory = new Configuration().configure().buildSessionFactory();
}
catch (Throwable ex)
{
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
ManageEmployee ME = new ManageEmployee();
/* Let us have a set of certificates for the first employee */
HashSet set1 = new HashSet();
set1.add(new Certificate("MCA"));
set1.add(new Certificate("MBA"));
set1.add(new Certificate("PMP"));
/* Add employee records in the database */
Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);
/* Another set of certificates for the second employee */
HashSet set2 = new HashSet();
set2.add(new Certificate("BCA"));
set2.add(new Certificate("BA"));
/* Add another employee record in the database */
Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);
/* List down all the employees */
ME.listEmployees();
/* Update employee's salary records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* List down all the employees */
ME.listEmployees();
}
/* Method to add an employee record in the database */
public Integer addEmployee(String fname, String lname, int salary, Set cert)
{
Session session = factory.openSession();
Transaction tx = null;
Integer employeeID = null;
try
{
tx = session.beginTransaction();
Employee employee = new Employee(fname, lname, salary);
employee.setCertificates(cert);
employeeID = (Integer) session.save(employee);
tx.commit();
}
catch (HibernateException e)
{
if (tx != null)
tx.rollback();
e.printStackTrace();
}
finally
{
session.close();
}
return employeeID;
}
/* Method to list all the employees detail */
public void listEmployees()
{
Session session = factory.openSession();
Transaction tx = null;
try
{
tx = session.beginTransaction();
List employees = session.createQuery("FROM Employee").list();
for (Iterator iterator1 = employees.iterator(); iterator1.hasNext();)
{
Employee employee = (Employee) iterator1.next();
System.out.print("First Name: " + employee.getFirstName());
System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
Set certificates = employee.getCertificates();
for (Iterator iterator2 = certificates.iterator(); iterator2.hasNext();)
{
Certificate certName = (Certificate) iterator2.next();
System.out.println("Certificate: " + certName.getName());
}
}
tx.commit();
}
catch (HibernateException e)
{
if (tx != null)
tx.rollback();
e.printStackTrace();
}
finally
{
session.close();
}
}
/* Method to update salary for an employee */
public void updateEmployee(Integer EmployeeID, int salary)
{
Session session = factory.openSession();
Transaction tx = null;
try
{
tx = session.beginTransaction();
Employee employee = (Employee) session.get(Employee.class, EmployeeID);
employee.setSalary(salary);
session.update(employee);
tx.commit();
}
catch (HibernateException e)
{
if (tx != null)
tx.rollback();
e.printStackTrace();
}
finally
{
session.close();
}
}
/* Method to delete an employee from the records */
public void deleteEmployee(Integer EmployeeID)
{
Session session = factory.openSession();
Transaction tx = null;
try
{
tx = session.beginTransaction();
Employee employee = (Employee) session.get(Employee.class, EmployeeID);
session.delete(employee);
tx.commit();
}
catch (HibernateException e)
{
if (tx != null)
tx.rollback();
e.printStackTrace();
}
finally
{
session.close();
}
}
}运行结果：
数据库中：
IDE控制台：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into EMPLOYEE (first_name, last_name, salary) values (?, ?, ?)
Hibernate: insert into CERTIFICATE (certificate_name) values (?)
Hibernate: insert into CERTIFICATE (certificate_name) values (?)
Hibernate: insert into CERTIFICATE (certificate_name) values (?)
Hibernate: update CERTIFICATE set employee_id=? where id=?
Hibernate: update CERTIFICATE set employee_id=? where id=?
Hibernate: update CERTIFICATE set employee_id=? where id=?
Hibernate: insert into EMPLOYEE (first_name, last_name, salary) values (?, ?, ?)
Hibernate: insert into CERTIFICATE (certificate_name) values (?)
Hibernate: insert into CERTIFICATE (certificate_name) values (?)
Hibernate: update CERTIFICATE set employee_id=? where id=?
Hibernate: update CERTIFICATE set employee_id=? where id=?
Hibernate: select employee0_.id as id0_, employee0_.first_name as first2_0_, employee0_.last_name as last3_0_, employee0_.salary as salary0_ from EMPLOYEE employee0_
First Name: Manoj Last Name: Kumar Salary: 4000
Hibernate: select certificat0_.employee_id as employee3_1_, certificat0_.id as id1_, certificat0_.id as id1_0_, certificat0_.certificate_name as certific2_1_0_ from CERTIFICATE certificat0_ where certificat0_.employee_id=?
Certificate: MBA
Certificate: MCA
Certificate: PMP
First Name: Dilip Last Name: Kumar Salary: 3000
Hibernate: select certificat0_.employee_id as employee3_1_, certificat0_.id as id1_, certificat0_.id as id1_0_, certificat0_.certificate_name as certific2_1_0_ from CERTIFICATE certificat0_ where certificat0_.employee_id=?
Certificate: BA
Certificate: BCA
Hibernate: select employee0_.id as id0_0_, employee0_.first_name as first2_0_0_, employee0_.last_name as last3_0_0_, employee0_.salary as salary0_0_ from EMPLOYEE employee0_ where employee0_.id=?
Hibernate: update EMPLOYEE set first_name=?, last_name=?, salary=? where id=?
Hibernate: select employee0_.id as id0_0_, employee0_.first_name as first2_0_0_, employee0_.last_name as last3_0_0_, employee0_.salary as salary0_0_ from EMPLOYEE employee0_ where employee0_.id=?
Hibernate: select certificat0_.employee_id as employee3_1_, certificat0_.id as id1_, certificat0_.id as id1_0_, certificat0_.certificate_name as certific2_1_0_ from CERTIFICATE certificat0_ where certificat0_.employee_id=?
Hibernate: update CERTIFICATE set employee_id=null where employee_id=?
Hibernate: delete from CERTIFICATE where id=?
Hibernate: delete from CERTIFICATE where id=?
Hibernate: delete from EMPLOYEE where id=?
Hibernate: select employee0_.id as id0_, employee0_.first_name as first2_0_, employee0_.last_name as last3_0_, employee0_.salary as salary0_ from EMPLOYEE employee0_
First Name: Manoj Last Name: Kumar Salary: 5000
Hibernate: select certificat0_.employee_id as employee3_1_, certificat0_.id as id1_, certificat0_.id as id1_0_, certificat0_.certificate_name as certific2_1_0_ from CERTIFICATE certificat0_ where certificat0_.employee_id=?
Certificate: MBA
Certificate: MCA
Certificate: PMP
参考文献：
英文：http://www.tutorialspoint.com/hibernate/hibernate_one_to_many_mapping.htm