Hibernate 联系关系映射之多对一

Hibernate 关联映射之多对一

Hibernate的关联映射包括：

一对一（Persion - IDCard）

一对多（Department - Employee）

多对一（Employee - Department）

多对多（Teacher - Student）

组件映射（User - Name）

集合映射（Set、List、Map）

inverse和cascade（Employee - Department）

本文以多对一为例：

多个员工对应一个部门（Employee - Department）

映射文件 <many-to-one name="depart" column="depart_id">

实体类：Department.java 和 Employee.java

package com.cos.entity;
/**
 * 部门
 * @author wangjy
 */
public class Department {
	private int id;
	private String 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;
	}
}

package com.cos.entity;
/**
 * 员工
 * @author wangjy
 */
public class Employee {
	private int id;
	private String name;
	private Department dept;
	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 Department getDept() {
		return dept;
	}
	public void setDept(Department dept) {
		this.dept = dept;
	}
}

映射文件：Department.hbm.xml 和 Employee.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.cos.entity">
	<class name="Department" lazy="true">
		<id name="id">
			<generator class="native"/>
		</id>	
		<property name="name"/>
	</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.cos.entity.Employee" lazy="true">
		<id name="id">
			<generator class="native"/>
		</id>	
		<property name="name"/>
		<many-to-one name="dept"/>
	</class>
</hibernate-mapping>

Hibernate配置文件：hibernate.cfg.xml

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql:///hi</property>
        <property name="hibernate.connection.username"></property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.hbm2ddl.auto">create</property>
        <property name="show_sql">true</property>
		<mapping resource="com/cos/entity/Employee.hbm.xml"/>
		<mapping resource="com/cos/entity/Department.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

工具类：HibernateUtil.java

package com.cos.util;

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

public final class HibernateUtil {

	private static SessionFactory sesseionFactory;

	static {
		Configuration conf = new Configuration();
		conf.configure();
		sesseionFactory = conf.buildSessionFactory();
	}

	public static SessionFactory getSesseionFactory() {
		return sesseionFactory;
	}
}

测试类：

package com.cos.main;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import com.cos.entity.Department;
import com.cos.entity.Employee;
import com.cos.util.HibernateUtil;

public class Many2One {

	public static void main(String[] args) {
		add();
	}
	public static void add(){
		SessionFactory  sessionFactory = null;
		Session s = null;
		Transaction t = null;
		try{
			sessionFactory = HibernateUtil.getSesseionFactory();
			s = sessionFactory.openSession();
			t = s.beginTransaction();
			Department dept = new Department();
			dept.setName("dept name 2");
			Employee emp = new Employee();
			emp.setName("emp name 2");
			emp.setDept(dept);
			s.save(dept);
			s.save(emp);
			t.commit();
			s.close();
			sessionFactory.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}

表结构：department表和employee表

CREATE TABLE `department` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1

CREATE TABLE `employee` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) default NULL,
  `dept` int(11) default NULL,
  PRIMARY KEY  (`id`),
  KEY `FK4AFD4ACE66A70F4E` (`dept`),
  CONSTRAINT `FK4AFD4ACE66A70F4E` FOREIGN KEY (`dept`) REFERENCES `department` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1

mysql> desc department;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name | varchar(255) | YES |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
mysql> desc employee;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name | varchar(255) | YES |     | NULL    |                |
| dept | int(11)      | YES | MUL | NULL    |                |
+-------+--------------+------+-----+---------+----------------+

Hibernate 联系关系映射之多对一

相关推荐