Hibernate Many-to-Many Mappings

创建表：

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)
);


create table CERTIFICATE (
   id INT NOT NULL auto_increment,
   certificate_name VARCHAR(30) default NULL,
   PRIMARY KEY (id)
);

中间表：

create table EMP_CERT (
   employee_id INT NOT NULL,
   certificate_id INT NOT NULL,
   PRIMARY KEY (employee_id,certificate_id)
);

POJO 类：

package com.jiangge.hblearn;

import java.util.*;

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;
	}
}

配置文件：

	
		org.hibernate.dialect.MySQLDialect
		com.mysql.jdbc.Driver

		
		jdbc:mysql://localhost/testMany2Many
		root
		root
		true
		
		
		

	

映射文件（写到一个文件中了 Employee.hbm.xml）：

 



   
       This class contains the employee detail. 
      
         
      
      
         
         
      
      
      
      
   

   
      This class contains the certificate records. 
      
         
      
      
   

测试：

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;

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 certificates = new HashSet();

		certificates.add(new Certificate("MCA"));
		certificates.add(new Certificate("MBA"));
		certificates.add(new Certificate("PMP"));

		/* Add employee records in the database */
		Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, certificates);

		/* Add another employee record in the database */
		Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, certificates);

		/* 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();
		}
	}
}

数据库结果：

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 22 | Manoj      | Kumar     |   5000 |
+----+------------+-----------+--------+
1 row in set (0.00 sec)

mysql> select * from CERTIFICATE;
+----+------------------+
| id | certificate_name |
+----+------------------+
|  4 | MBA              |
|  5 | PMP              |
|  6 | MCA              |
+----+------------------+
3 rows in set (0.00 sec)

mysql> select * from EMP_CERT;
+-------------+----------------+
| employee_id | certificate_id |
+-------------+----------------+
|          22 |              4 |
|          22 |              5 |
|          22 |              6 |
+-------------+----------------+
3 rows in set (0.00 sec)

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