hibernate关联关系（一对多）

1.什么是关联关系？

关联关系是指两个实体或者表有相互关联，比如在订单表中，订单项表有订单id，那么订单项表中的订单id就关联订单项表中订单Id字段。因此关联关系，可以看成是一种外键关系。

2.为什么要有关联关系？

为了实现级联操作，删除订单中某个列段，会连带删除订单项表中相对应的列段，以便维护表数据的一致性。

配置文件：

SessionFactoryUtils

package com.chenjiahao.two.util;

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

public class SessionFactoryUtils {
	private static SessionFactory sessionFactory;
	static {
		Configuration cfg = new Configuration().configure("hibernate.cfg.xml");
		sessionFactory = cfg.buildSessionFactory();
	}
	
	public static Session openSession() {
		Session session = sessionFactory.getCurrentSession();
		if(session == null) {
			session = sessionFactory.openSession();
		}
		return session;
	}
	
	public static void closeSession() {
		Session session = sessionFactory.getCurrentSession();
		if(session != null && session.isOpen()) {
			session.close();
		}
	}
	
	public static void main(String[] args) {
		Session session = SessionFactoryUtils.openSession();
		session.beginTransaction();
		System.out.println(session.isConnected());
		SessionFactoryUtils.closeSession();
		System.out.println(session.isConnected());
	}
}

　　实体类配置文件：

Order

package com.chenjiahao.three.entity;

import java.util.ArrayList;
import java.util.List;

public class Order {

	private Integer orderId;
	private String orderNo;
	//建立了关联关系，一个订单对应多个订单项
    private List<OrderItem> orderItems=new ArrayList<>();
    private Integer initChildren=0;//0是懒加载 1，fasle
    
    
	public Integer getInitChildren() {
		return initChildren;
	}

	public void setInitChildren(Integer initChildren) {
		this.initChildren = initChildren;
	}

	public List<OrderItem> getOrderItems() {
		return orderItems;
	}

	public void setOrderItems(List<OrderItem> orderItems) {
		this.orderItems = orderItems;
	}

	public Integer getOrderId() {
		return orderId;
	}

	public void setOrderId(Integer orderId) {
		this.orderId = orderId;
	}

	public String getOrderNo() {
		return orderNo;
	}

	public void setOrderNo(String orderNo) {
		this.orderNo = orderNo;
	}

	@Override
	public String toString() {
		return "Order [orderId=" + orderId + ", orderNo=" + orderNo + "]";
	}

}

　　OrderItem

package com.chenjiahao.three.entity;

public class OrderItem {

	private Integer orderItemId;
	private Integer productId;
	private Integer quantity;
	private Integer oid;
	//建立关联关系 一个订单对应的是一个订单
	private Order order;
	

	public Order getOrder() {
		return order;
	}

	public void setOrder(Order order) {
		this.order = order;
	}

	public Integer getOrderItemId() {
		return orderItemId;
	}

	public void setOrderItemId(Integer orderItemId) {
		this.orderItemId = orderItemId;
	}

	public Integer getProductId() {
		return productId;
	}

	public void setProductId(Integer productId) {
		this.productId = productId;
	}

	public Integer getQuantity() {
		return quantity;
	}

	public void setQuantity(Integer quantity) {
		this.quantity = quantity;
	}

	public Integer getOid() {
		return oid;
	}

	public void setOid(Integer oid) {
		this.oid = oid;
	}

	@Override
	public String toString() {
		return "OrderItem [orderItemId=" + orderItemId + ", productId=" + productId + ", quantity=" + quantity
				+ ", oid=" + oid + "]";
	}

}

　　配置hibernate.cfg.xml（红色字体）

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
	<hibernate-configuration>
	<session-factory>
		<!-- 1. 数据库相关 -->
		<property name="connection.username">root</property>
		<property name="connection.password">123</property>
		<property name="connection.url">jdbc:mysql://localhost:3306/T224?useUnicode=true&characterEncoding=UTF-8
		</property>
		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

		<!-- 配置本地事务（No CurrentSessionContext configured!） -->
		<property name="hibernate.current_session_context_class">thread</property>

		<!-- 2. 调试相关 -->
		<property name="show_sql">true</property>
		<property name="format_sql">true</property>

		<!-- 3. 添加实体映射文件 -->
		<mapping resource="com/chenjiahao/one/entity/User.hbm.xml"/>
		<!-- 讲解主键生成 策略-->
		<mapping resource="com/chenjiahao/two/entity/Student.hbm.xml"/>	
		<mapping resource="com/chenjiahao/two/entity/Worker.hbm.xml"/>
		<!-- 一对多 -->
		<mapping resource="com/chenjiahao/three/entity/OrderItem.hbm.xml"/>	
        <mapping resource="com/chenjiahao/three/entity/Order.hbm.xml"/>	
	</session-factory>
</hibernate-configuration>

实体类xml配置文件：

bag标签：
lazy：是否懒加载，默认是懒加载的 true
name:类的关联属性名
cascade:级联关系级联新增与修改
inverse：关联关系交给对方控制默认是true，当前类不维护关联关系

子标签key:
column:主表的主键，从标的外键

子标签one-to-many：外键对应的实体类

Order.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.chenjiahao.three.entity.Order" table="t_hibernate_order">
		<id name="orderId" type="java.lang.Integer" column="order_id">
			<generator class="increment" />
		</id>
		<property name="orderNo" type="java.lang.String" column="order_no">
		</property>
	<bag lazy="true" name="orderItems" cascade="save-update" inverse="true">
		       <key column="oid"></key>
		       <one-to-many class="com.chenjiahao.three.entity.OrderItem"/>
		</bag>
	</class>

</hibernate-mapping>

OrderItem.hbm.xml

insert="fasle' update ="fasle" 这个属性只能给一个oid

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.chenjiahao.three.entity.OrderItem" table="t_hibernate_order_item">
		<id name="orderItemId" type="java.lang.Integer" column="order_item_id">
			<generator class="increment" />
		</id>
		<property name="productId" type="java.lang.Integer" column="product_id">
		</property>
		<property name="quantity" type="java.lang.Integer" column="quantity">
		</property>
		<!--  Repeated column in mapping for entity -->
		<property name="oid" type="java.lang.Integer" column="oid" insert="false" update="false">
		</property>
		<many-to-one name="order" class="com.chenjiahao.three.entity.Order" column="oid"></many-to-one>
	</class>
</hibernate-mapping>

　　DemoDao

package com.chenjiahao.three.dao;

import java.util.List;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.chenjiahao.three.entity.Order;
import com.chenjiahao.three.entity.OrderItem;
import com.chenjiahao.two.util.SessionFactoryUtils;

public class DemoDao {
	/**
	 * 为了测试关系型映射文件配置准确
	 * 	讲解insert=false，update=false的用途
	 * @param order
	 * @return
	 */
	public Integer addOrder(Order order) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Integer oid = (Integer)session.save(order);
		transaction.commit();
		session.close();
		return oid;
	}
	
	public Integer addOrderItem(OrderItem orderItem) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Integer otid = (Integer)session.save(orderItem);
		transaction.commit();
		session.close();
		return otid;
	}
	
	
	
	/**
	 * 为了讲解懒加载的问题（hibernate3.0后所有查询方式默认采用的是懒加载方式）
	 * 	1、查单个时存在问题，代理对象已经关闭
	 * 	2、查多个存在问题，有性能的问题
	 * @param order
	 * @return
	 */
	public Order getOrder(Order order) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Order o = session.get(Order.class, order.getOrderId());
		if(o != null && new Integer(1).equals(order.getInitChildren())) {
			//强制加载关联对象
			Hibernate.initialize(o.getOrderItems());
//			System.out.println(o.getOrderItems());
		}
		transaction.commit();
		session.close();
		return o;
	}
	
	public List<Order> getOrderList() {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		List<Order> list = session.createQuery("from Order").list();
		transaction.commit();
		session.close();
		return list;
	}
	
	/**
	 * z主表的数据不能随便删除，得先删除从表中对应信息，才能删除主表的信息。
	 * @param order
	 */
	public void delOrder(Order order) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Order order2 = session.get(Order.class, order.getOrderId());
		for (OrderItem oi : order2.getOrderItems()) {
			session.delete(oi);
		}
		session.delete(order2);
//		session.delete(order);
		transaction.commit();
		session.close();
	}
}

　　测试：junit

package com.chenjiahao.three.dao;

import static org.junit.Assert.*;

import java.util.List;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.chenjiahao.three.entity.Order;
import com.chenjiahao.three.entity.OrderItem;
/**
 * @Before每测试一个@test标记的测试方法，都会调用之前执行一次
 * @After每测试一个@test标记的测试方法，都会调用之后执行一次
 * @author dell
 *
 */
public class DemoDaoTest {
  
	 private DemoDao demoDao=new DemoDao();
//	@Before
//	public void setUp() throws Exception {
//		System.out.println("加载资源");
//	}
//
//	@After
//	public void tearDown() throws Exception {
//		System.out.println("释放资源");
//	}

	@Test//同时给两张表添加数据
	public void testAddOrder() {
		Order order=new Order();
		order.setOrderNo("honor20");//订单编号，因为id是自增列不用管
		OrderItem orderItem =null;
		for (int i = 0; i < 6; i++) {
			orderItem = new OrderItem();
			orderItem.setProductId(19+i);
			orderItem.setQuantity(26+i);
			//维护关系
			orderItem.setOrder(order);//给订单项里面的属性赋值
			order.getOrderItems().add(orderItem);
		}
		demoDao.addOrder(order);
		
	}

	@Test//给原有的订单表添加订单项
	public void testAddOrderItem() {
		//添加一条数据
//		OrderItem orderItem = new OrderItem();
//		orderItem.setProductId(12);
//		orderItem.setQuantity(41);
//		Order order=new Order();
//		order.setOrderId(2);
//		order.getOrderItems().add(orderItem);
//		orderItem.setOrder(order);
//		demoDao.addOrderItem(orderItem);
		//添加多条数据
	    OrderItem orderItem = null;		
		for (int i = 0; i < 6; i++) {
			orderItem = new OrderItem();
			orderItem.setProductId(10+i);
			orderItem.setQuantity(20+i);
			//维护关系
			Order order=new Order();
			order.setOrderId(2);//订单id
			order.getOrderItems().add(orderItem);
			orderItem.setOrder(order);
			demoDao.addOrderItem(orderItem);
		}
	}

	@Test
	public void testGetOrder() {
		Order order = new Order();
		order.setOrderId(3);
		order.setInitChildren(1);
		Order o = this.demoDao.getOrder(order);
		//failed to lazily initialize a collection of role: 
		//com.chenjiahao.three.entity.Order.orderItems, 
		//could not initialize proxy - no Session
		//原因：操作了两次数据库，当layz等于false的时候，会让hibernate执行两次操作，session才会关闭
		//当layz等于true的时候，会让hibernate执行一次操作，session就会关闭
		//从上面看layz等于false更好，但是为什么hibernate默认让它等于true?
		//处于性能的考虑，所以hibernate3.0出现lazy这个属性，并让它默认等于true，也就是说不加载关联属性
		List<OrderItem> orderItems = o.getOrderItems();
		for (OrderItem orderItem : orderItems) {
			System.out.println(orderItem);
		}
		System.out.println("id为3的订单:"+o);
		
	}

	@Test
	public void testGetOrderList() {
		List<Order> orderList = this.demoDao.getOrderList();
		for (Order order : orderList) {
			for (OrderItem orderItem : order.getOrderItems()) {
				System.out.println(orderItem);
			}
			System.out.println(order);
		}
	}

	@Test
	public void testDelOrder() {
		Order order=new Order();
		order.setOrderId(2);
		this.demoDao.delOrder(order);
	}

}

懒加载:

只有在使用时，他才会发出SQL语句，查询数据，如果不使用对象则不会发出SQL语句进行查询。

Hibernate的lazy生效期：
生效期和session一样的，session关闭，lazy失效
hibernate支持lazy策略只在session打开状态下有效

	@Test
	public void testGetOrder() {
		Order order = new Order();
		order.setOrderId(3);
		order.setInitChildren(1);
		Order o = this.demoDao.getOrder(order);
		//failed to lazily initialize a collection of role: 
		//com.chenjiahao.three.entity.Order.orderItems, 
		//could not initialize proxy - no Session
		//原因：操作了两次数据库，当layz等于false的时候，会让hibernate执行两次操作，session才会关闭

		List<OrderItem> orderItems = o.getOrderItems();
		for (OrderItem orderItem : orderItems) {
			System.out.println(orderItem);
		}
		System.out.println("id为3的订单:"+o);
		
	}

　　在order类中（也就是主表）加一个属性：

 private Integer initChildren=0;//0是懒加载 1，fasle

　　在domedao类里的get加：

public Order getOrder(Order order) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Order o = session.get(Order.class, order.getOrderId());
		if(o != null && new Integer(1).equals(order.getInitChildren())) {
			//强制加载关联对象
			Hibernate.initialize(o.getOrderItems());
//			System.out.println(o.getOrderItems());
		}
		transaction.commit();
		session.close();
		return o;
	}

　　从而可以控制是否懒加载

hibernate框架一对多的执行原理：
1、对hibernate.cfg.xml进行建模，等到sessionfactory对象
2、并且拿到mapping resoutrce里的内容
3、拿到了Order.hbm.xml配置文件
4、可以再次建模，拿到com.chenjiahao.three.entity.Order（实体类），以及t_hibernate_order（数据库表名）
类属性，以及表列段
5、生成动态的sql：select ordeerId,orderNo from t_hibernate_order;
执行sql最终得到meterDate源数据模型
ordeerId,orderNo
1 p20
3 p30
6、Order o1=Class.forName().newInstance();
o1.setOrderId(1);
o1.setOrderNo(p1);
.....
最终得到：
List<Order> List=new ArrayList();
List.add(01);
...
最终list中的所有order实列都有值了：（这里只是处理表里的非外加列段，原理完全跟baseDao一样）

7、处理关联关系：（通过建模可以得到Order.hbm.xml所有的属性）orderItems oid com.chenjiahao.three.entity.OrderItem
通过one-to-many这个标签以及calss对应的全路径名对应的专属映射文件
也就是找到了Order.item.xml文件，拿到了它之后就可以拿到table t_hibernate_order_item
8、select * from t_hibernate_order_item;
最终得到一个list<OrderItem> orderItems
9、给order的关联关系属性赋值
List<Order> List=new ArrayList();
for(Order o: list){
o.setOrderItems(orderItems);
}

posted @ 2019-07-15 20:36 chenjiahao 阅读(297) 评论(0) 编辑收藏举报

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