Hibernate ManyToOne Mappings 多对一关联映射

Hibernate ManyToOne Mappings 多对一关联映射

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，即事实上例须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编写訪问数据库的代码

样例：多个员工相应一个地址。

一、创建hibernate.cfg.xml 配置文件：

注意数据库名、用户名、密码是否填写正确。

<?xml version="1.0" encoding="utf-8"?

>
<!DOCTYPE hibernate-configuration SYSTEM
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

		<!-- Assume testone is the database name -->
		<property name="hibernate.connection.url">jdbc:mysql://localhost/testMany2One</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">root</property>
		<property name="hibernate.show_sql">true</property>

		<!-- List of XML mapping files -->
		<mapping resource="resource/Employee.hbm.xml" />

	</session-factory>
</hibernate-configuration>

二、创建持久化类。即事实上例须要保存到数据库中的类（Employee.java、Address.java）

Employee.java

package com.jiangge.hblearn;

/**
 * @author jiangge
 */
public class Employee
{
	private int id;
	private String firstName;
	private String lastName;
	private int salary;
	private Address address;

	public Employee()
	{
	}

	public Employee(String firstName, String lastName, int salary,
			Address address)
	{
		this.firstName = firstName;
		this.lastName = lastName;
		this.salary = salary;
		this.address = address;
	}

	public int getId()
	{
		return id;
	}

	public void setId(int id)
	{
		this.id = id;
	}

	public String getFirstName()
	{
		return firstName;
	}

	public void setFirstName(String firstName)
	{
		this.firstName = firstName;
	}

	public String getLastName()
	{
		return lastName;
	}

	public void setLastName(String lastName)
	{
		this.lastName = lastName;
	}

	public int getSalary()
	{
		return salary;
	}

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

	public Address getAddress()
	{
		return address;
	}

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

Address.java

package com.jiangge.hblearn;

/**
 * @author shijiangge
 * @version 2014-7-4 上午11:05:39
 *
 */
public class Address
{
	private int id;
	private String street;
	private String city;
	private String state;
	private String zipcode;

	public Address()
	{
	}

	public Address(String street, String city, String state, String zipcode)
	{
		this.street = street;
		this.city = city;
		this.state = state;
		this.zipcode = zipcode;
	}

	public int getId()
	{
		return id;
	}

	public void setId(int id)
	{
		this.id = id;
	}

	public String getStreet()
	{
		return street;
	}

	public void setStreet(String street)
	{
		this.street = street;
	}

	public String getCity()
	{
		return city;
	}

	public void setCity(String city)
	{
		this.city = city;
	}

	public String getState()
	{
		return state;
	}

	public void setState(String state)
	{
		this.state = state;
	}

	public String getZipcode()
	{
		return zipcode;
	}

	public void setZipcode(String zipcode)
	{
		this.zipcode = zipcode;
	}
}

在MySQL中创建表：

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,
   address    INT NOT NULL,
   PRIMARY KEY (id)
);

create table ADDRESS (
   id INT NOT NULL auto_increment,
   street_name VARCHAR(40) default NULL,
   city_name VARCHAR(40) default NULL,
   state_name VARCHAR(40) default NULL,
   zipcode VARCHAR(10) default NULL,
   PRIMARY KEY (id)
);

三、创建对象-关系映射文件（Employee.hbm.xml）

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<!--
Hibernate Many-to-One 关联关系：
非常多员工能够相应一个地址。

0基础的程序猿手写 Employee.hbm.xml 映射文件，而高级程序猿使用XDoclet, Middlegen and AndroMDA这些技术，自己主动生成映射文件。

meta 标签是可选的，用来描写叙述类。

Hibernate的主键生成策略：
【identity】採用数据库提供的主键生成机制。

如DB2、SQL Server、MySQL 中的主键生成机制。

【native】由 Hibernate 依据使用的数据库自行推断採用 identity、hilo、sequence 当中一种作为主键生成方式。

-->
<hibernate-mapping>
	<class name="com.jiangge.hblearn.Employee" table="EMPLOYEE">
		<meta attribute="class-description">
			This class contains the employee detail.
		</meta>
		<id name="id" type="int" column="id">
			<generator class="native" />
		</id>
		<property name="firstName" column="first_name" type="string" />
		<property name="lastName" column="last_name" type="string" />
		<property name="salary" column="salary" type="int" />
		<many-to-one name="address" column="address" class="com.jiangge.hblearn.Address" not-null="true" />
	</class>

	<class name="com.jiangge.hblearn.Address" table="ADDRESS">
		<meta attribute="class-description">
			This class contains the address detail.
		</meta>
		<id name="id" type="int" column="id">
			<generator class="native" />
		</id>
		<property name="street" column="street_name" type="string" />
		<property name="city" column="city_name" type="string" />
		<property name="state" column="state_name" type="string" />
		<property name="zipcode" column="zipcode" type="string" />
	</class>

</hibernate-mapping>

四、通过Hibernate API编写訪问数据库的代码

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.Address;
import com.jiangge.hblearn.Employee;

/**
 * 測试类：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 one address object */
		Address address = ME.addAddress("Kondapur", "Hyderabad", "AP", "532");

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

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

		/* 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 address record in the database */
	public Address addAddress(String street, String city, String state, String zipcode)
	{
		Session session = factory.openSession();
		Transaction tx = null;
		Integer addressID = null;
		Address address = null;
		try
		{
			tx = session.beginTransaction();
			address = new Address(street, city, state, zipcode);
			addressID = (Integer) session.save(address);
			tx.commit();
		}
		catch (HibernateException e)
		{
			if (tx != null)
				tx.rollback();
			e.printStackTrace();
		}
		finally
		{
			session.close();
		}
		return address;
	}

	/* Method to add an employee record in the database */
	public Integer addEmployee(String fname, String lname, int salary,
			Address address)
	{
		Session session = factory.openSession();
		Transaction tx = null;
		Integer employeeID = null;
		try
		{
			tx = session.beginTransaction();
			Employee employee = new Employee(fname, lname, salary, address);
			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 iterator = employees.iterator(); iterator.hasNext();)
			{
				Employee employee = (Employee) iterator.next();
				System.out.print("First Name: " + employee.getFirstName());
				System.out.print("  Last Name: " + employee.getLastName());
				System.out.println("  Salary: " + employee.getSalary());
				Address add = employee.getAddress();
				System.out.println("Address ");
				System.out.println("\tStreet: " + add.getStreet());
				System.out.println("\tCity: " + add.getCity());
				System.out.println("\tState: " + add.getState());
				System.out.println("\tZipcode: " + add.getZipcode());
			}
			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();
		}
	}
}

五、执行结果：

mysql>  select * from EMPLOYEE;
+----+------------+-----------+--------+---------+
| id | first_name | last_name | salary | address |
+----+------------+-----------+--------+---------+
|  1 | Manoj      | Kumar     |   5000 |       1 |
+----+------------+-----------+--------+---------+
1 row in set

mysql> select * from ADDRESS;
+----+-------------+-----------+------------+---------+
| id | street_name | city_name | state_name | zipcode |
+----+-------------+-----------+------------+---------+
|  1 | Kondapur    | Hyderabad | AP         | 532     |
+----+-------------+-----------+------------+---------+
1 row in set

mysql> 

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: insert into ADDRESS (street_name, city_name, state_name, zipcode) values (?, ?

, ?

, ?)
Hibernate: insert into EMPLOYEE (first_name, last_name, salary, address) values (?, ?, ?

, ?)
Hibernate: insert into EMPLOYEE (first_name, last_name, salary, address) values (?, ?, ?, ?

)
Hibernate: select employee0_.id as id0_, employee0_.first_name as first2_0_, employee0_.last_name as last3_0_, employee0_.salary as salary0_, employee0_.address as address0_ from EMPLOYEE employee0_
First Name: Manoj  Last Name: Kumar  Salary: 4000
Address
Hibernate: select address0_.id as id1_0_, address0_.street_name as street2_1_0_, address0_.city_name as city3_1_0_, address0_.state_name as state4_1_0_, address0_.zipcode as zipcode1_0_ from ADDRESS address0_ where address0_.id=?

Street: Kondapur
	City: Hyderabad
	State: AP
	Zipcode: 532
First Name: Dilip  Last Name: Kumar  Salary: 3000
Address
	Street: Kondapur
	City: Hyderabad
	State: AP
	Zipcode: 532
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_, employee0_.address as address0_0_ from EMPLOYEE employee0_ where employee0_.id=?
Hibernate: update EMPLOYEE set first_name=?, last_name=?, salary=?, address=? 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_, employee0_.address as address0_0_ from EMPLOYEE employee0_ where employee0_.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_, employee0_.address as address0_ from EMPLOYEE employee0_
First Name: Manoj  Last Name: Kumar  Salary: 5000
Address
Hibernate: select address0_.id as id1_0_, address0_.street_name as street2_1_0_, address0_.city_name as city3_1_0_, address0_.state_name as state4_1_0_, address0_.zipcode as zipcode1_0_ from ADDRESS address0_ where address0_.id=?
	Street: Kondapur
	City: Hyderabad
	State: AP
	Zipcode: 532

參考文献：

http://www.tutorialspoint.com/hibernate/hibernate_many_to_one_mapping.htm