Hibernate关联映射之多对一/一对多双向关联映射

多对一和一对多双向关联映射是一回事

方法一：使用Annotation实现

（1）建立Depart类和Employee类

package com.model;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Depart {
	private int id;
	private String name;
	private Set employees = new HashSet();
	@Id
	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;
	}
	@OneToMany(mappedBy="depart")
	public Set getEmployees() {
		return employees;
	}
	public void setEmployees(Set employees) {
		this.employees = employees;
	}
}

package com.model;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Employee {
	private int id;
	private String name;
	private Depart depart;
	@Id
	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;
	}
	@ManyToOne
	public Depart getDepart() {
		return depart;
	}
	public void setDepart(Depart depart) {
		this.depart = depart;
	}
	
}

----------双向映射必设mappedBy----------

（2）设置Hibernate配置文件hibernate.cfg.xml

	
		
		com.mysql.jdbc.Driver
		
		jdbc:mysql://localhost:3306/hibernate
		
		root
		
		
		
		org.hibernate.dialect.MySQLDialect
		
        true
        true
		
		create
		
		thread
		
		
		

（3）建立测试类，此处使用Junit4进行测试，仅仅测试一对一映射如何建表即可。

package com.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.Test;

public class ORMappingTest {

	@Test
	public void test() {
		Configuration cfg = new Configuration();
		cfg.configure();
		ServiceRegistry  sr = new ServiceRegistryBuilder().applySettings(cfg.getProperties()).buildServiceRegistry(); 
		SessionFactory  sf = cfg.buildSessionFactory(sr);
		Session s = sf.getCurrentSession();
		Transaction tx = s.beginTransaction();
		
		tx.commit();
		sf.close();
	}

}

（4）运行测试类，查看后台输出的建表SQL语句。

Hibernate: 
    create table Depart (
        id integer not null,
        name varchar(255),
        primary key (id)
    )
Hibernate: 
    create table Employee (
        id integer not null,
        name varchar(255),
        depart_id integer,
        primary key (id)
    )
Hibernate: 
    alter table Employee 
        add index FK4AFD4ACE7F7C470C (depart_id), 
        add constraint FK4AFD4ACE7F7C470C 
        foreign key (depart_id) 
        references Depart (id)

方法二：使用映射文件hbm.xml实现：

（1）建立Depart类和Employee类，在方法一的基础上去掉@注解即可。

（2）建立映射文件Depart.hbm.xml和Employee.hbm.xml

---------特别注意的是这两个映射文件的column="depart_id"必须一致，否则表中则出现不同的外键字段-----------

（3）设置Hibernate配置文件hibernate.cfg.cml的映射文件

（4）运行方法一的测试类，得到相同的测试结果。