hibernate---->多对一关联映射

1、多对一关联映射

 <many-to-one>会在多的一端加入一个外键，指向一的一端(主键)，这个外键列名是由<many-to-one>中的column属性定义的，如果忽略了这个属性那么默认的外键与实体的属性一致
功能:
   a. 告诉数据库,多的一端有一个外键,参照一的一端主键.
   b. 告诉hibernate,在插入多的一端时,外键的插入会参照一的一端的主键.
   c. 告诉hibernate,在查找多的一端时,会自动查找一的一端的对象(多的一端外键 ---> 一的一端主键)

2、cascade级联 --  是对象的连锁操作
  * <many-to-one name="group" column="groupid" cascade="all"/>
  * cascade取值为: all, none, save-update, delete  --  在各种情况下的级联操作.

<?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.wsz.entity.User" table="t_user">
		<id name="id">
			<generator class="native" />
		</id>
		<property name="name" />
		<many-to-one name="group" column="groupid" cascade="all"/>
	</class>
</hibernate-mapping>

user.java

package com.wsz.entity;


public class User {
	private  int  id;
	private String name;
	private Group group ;
	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 Group getGroup() {
		return group;
	}
	public void setGroup(Group group) {
		this.group = group;
	}

	
	


}

group.java

publicclass Group {

  privte String id;

  private String name;

}

  publicclass User{

  private String id;

  privte String name;

  private Group group;

  public Group getGroup(){return group;}

  public void setGroup(Group group){

  this.group = group;

      }

级联添加

package com.wsz.test;

import junit.framework.TestCase;

import org.hibernate.Session;

import com.wsz.entity.Group;
import com.wsz.entity.HibernateUtils;
import com.wsz.entity.User;

public class TestManyToOne extends TestCase {

	public void testManyToOne() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			Group group = new Group();
			group.setName("CEIT");
			for (int i = 0; i < 10; i++) {
				User user = new User();
				user.setName("第" + i + "个");
				user.setGroup(group);
				session.save(user);
			}
			session.getTransaction().commit();
			User user = (User) session.load(User.class, 27);
			System.out.println(user.getGroup().getName());
		} catch (Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		} finally {
			HibernateUtils.closeSession(session);
		}

	}
}