Hibernate关联（一对多）

1.什么是关联(association)

1.1 关联指的是类之间的引用关系。如果类A与类B关联，那么被引用的类B将被定义为类A的属性

hibernate:orm框架、以面向对象的思想操作数据库
实体类 -->表
属性 -->字段
1.2 关联的分类：关联可以分为一对一、一对多/多对一、多对多关联,关联是有方向的

  
	  订单表、订单项表
	  select * from t_order t,t_orderItem m where t.oid = m.oid
	  and .....
	  
	  
	  class Order{
		private STIRNG OID;
		...
		private Set<OrderItem> OrderItems; 
	  }
	  
	  session.get(Order.class,1)

2.案例:如何建立客户和订单一对多双向关联

实体类与映射:
Order

package com.wupeng.three.entity;

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

public class Order {
	private Integer orderId;
	private String orderNo;
	private List<OrderItem> orderItems = new ArrayList<OrderItem>();
	private Integer ininChildren = 1;//1代表开启懒加载，0代表关闭懒加载
	public Order() {
		super();
	}
	public Order(Integer orderId, String orderNo) {
		super();
		this.orderId = orderId;
		this.orderNo = orderNo;
	}
	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;
	}
	
	public List<OrderItem> getOrderItems() {
		return orderItems;
	}
	public void setOrderItems(List<OrderItem> orderItems) {
		this.orderItems = orderItems;
	}
	
	
	public Integer getIninChildren() {
		return ininChildren;
	}
	public void setIninChildren(Integer ininChildren) {
		this.ininChildren = ininChildren;
	}
	@Override
	public String toString() {
		return "Order [orderId=" + orderId + ", orderNo=" + orderNo + ", orderItems=" + orderItems + "]";
	}
	
}

OrderItem

package com.wupeng.three.entity;

public class OrderItem {
	private Integer orderItemId;
	private Integer productId;
	private Integer quantity;
	private Integer oid;
	private 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;
	}
	
	
	public Order getOrder() {
		return order;
	}
	public void setOrder(Order order) {
		this.order = order;
	}

	public OrderItem(Integer orderItemId, Integer productId, Integer quantity, Integer oid) {
		super();
		this.orderItemId = orderItemId;
		this.productId = productId;
		this.quantity = quantity;
		this.oid = oid;
	}
	public OrderItem() {
		super();
	}
}

Order.hbm.xml（映射文件）

<?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.wupeng.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>
		<!-- 需要在映射文件中进行关联关系的维护 这里的描述是一对多的关系 -->
		<!-- 需要在映射文件中进行关系的维护  这里描述的是一对多的关系 -->
		<bag name="orderItems" cascade="save-update" inverse="true">
		   <!-- 从表的外键 -->
		   <key column="oid"></key>
		   <!-- 查询从表数据，然后形成list集合填充到orderItems属性中 -->
		   <one-to-many class="com.wupeng.three.entity.OrderItem"></one-to-many>
		   <!-- 
		         select * from t_hibernate_order_item where oid = 1
		   -->
		</bag>
	</class>

</hibernate-mapping>

OrderItem.hbm.xml（映射文件）

<?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.wupeng.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>
		<property name="oid" type="java.lang.Integer" column="oid" insert="false" update="false">
		</property>
		<!-- 需要在映射文件中进行关联关系的维护 这里的描述是多对一的关系 -->
		<many-to-one name="order" class="com.wupeng.three.entity.Order" column="oid"></many-to-one>
	</class>
</hibernate-mapping>

Dao包:
DemoDao

package com.wupeng.three.dao;

import java.util.List;

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

import com.wupeng.three.entity.Order;
import com.wupeng.three.entity.OrderItem;
import com.wupeng.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(0).equals(order.getIninChildren())) {
//		0代表强制关闭懒加载,也就意味着需要强制加载关联关系对象
			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();
	}
}

使用junit进行测试
DemoDaoTest

package com.wupeng.three.dao;

import static org.junit.Assert.*;

import java.util.List;

import org.junit.Test;

import com.wupeng.three.entity.Order;
import com.wupeng.three.entity.OrderItem;

public class DemoDaoTest {
private DemoDao demoDao=new DemoDao();
	@Test
	public void testAddOrder() {
		Order order=new Order();
		order.setOrderNo("wupeng");
		OrderItem oi=null;
		for (int i = 0; i < 3; i++) {
			oi = new OrderItem();
			oi.setProductId(11+i);
			oi.setQuantity(22+i);
			oi.setOrder(order);
			order.getOrderItems().add(oi);
		}
		demoDao.addOrder(order);
	}

	@Test
	public void testAddOrderItem() {
		Order order=new Order();
		order.setOrderId(5);
		OrderItem oi=null;
		for (int i = 0; i < 3; i++) {
			oi = new OrderItem();
			oi.setProductId(10+i);
			oi.setQuantity(20+i);
			oi.setOrder(order);
			order.getOrderItems().add(oi);
			demoDao.addOrderItem(oi);
		}
	}
/**
 * 关于懒加载的问题
 * hibernate3之后出现的
 */
	@Test
	public void testGetOrder() {
		Order order=new Order();
		order.setOrderId(10);
		order.setIninChildren(0);
		Order o = this.demoDao.getOrder(order);
		System.out.println(o.getOrderNo());
		System.out.println(o.getOrderItems());
	}
/**
 * 如果说将懒加载的功能关闭,也就是说lazy=false,那么在查询多条订单数据的情况下是非常影响性能的
 * 
 */
	@Test
	public void testGetOrderList() {
		List<Order> ordersList=this.demoDao.getOrderList();
		for (Order order : ordersList) {
			System.out.println(order.getOrderNo());
			System.out.println(order.getOrderItems());
		}
	}

	@Test
	public void testDelOrder() {
		Order order=new Order();
		order.setOrderId(10);
		this.demoDao.delOrder(order);
	}

}

测试添加方法

	@Test
	public void testAddOrder() {
		Order order=new Order();
		order.setOrderNo("wupeng");
		OrderItem oi=null;
		for (int i = 0; i < 3; i++) {
			oi = new OrderItem();
			oi.setProductId(11+i);
			oi.setQuantity(22+i);
			oi.setOrder(order);
			order.getOrderItems().add(oi);
		}
		demoDao.addOrder(order);
	}

运行时junit会报错,原因是映射文件OrderItem.hbm.xml映射了两次oid需property标签里面加上insert=“false” update="false

<property name="oid" type="java.lang.Integer" column="oid" insert="false" update="false">

懒加载

/**
 * 关于懒加载的问题
 * hibernate3之后出现的
 */
	@Test
	public void testGetOrder() {
		Order order=new Order();
		order.setOrderId(10);
		order.setIninChildren(0);
		Order o = this.demoDao.getOrder(order);
		System.out.println(o.getOrderNo());
		System.out.println(o.getOrderItems());
	}
/**
 * 如果说将懒加载的功能关闭,也就是说lazy=false,那么在查询多条订单数据的情况下是非常影响性能的
 * 
 */
	@Test
	public void testGetOrderList() {
		List<Order> ordersList=this.demoDao.getOrderList();
		for (Order order : ordersList) {
			System.out.println(order.getOrderNo());
			System.out.println(order.getOrderItems());
		}
	}

运行junit时会报错

failed to lazily initialize a collection of role:   com.wupeng.three.entity.Order.orderItems,  could not initialize proxy - no Session  

解决方法:

但这种解决方案会影响查询多条订单数据的性能,如果你需要查询多条数据不建议使用这种
推荐使用另一种方法来解决在Order这个实体类中加入

然后就是在我们的DemoDao里懒加载的问题

最后使用junit进行测试就可以了