hibernate之关联关系（一对多）

什么是关联(association)

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。例如:

  class B{
	private String name;
  }
  
  public class A{
    private B b = new B;
    public A(){}
      }

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

案例

今天我们基于上一篇博客的上面对hibernate进行一个改造

首先我们今天是对订单与订单项的查询，所以我们得创建两个表

-- 订单表(主表)
create table t_hibernate_order
(
  order_id int primary key auto_increment,
  order_no varchar(50) not null
);


-- 订单项表(从表)
create table t_hibernate_order_item
(
  order_item_id int primary key auto_increment,
  product_id int not null,
  quantity int not null,
  oid int not null,
  foreign key(oid) references t_hibernate_order(order_id)
);

创建完这两个表之后，我们加入实体类的配置文件
订单的配置文件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.yz.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标签
				lasy：是否懒加载：默认是懒加载的 true  懒汉模式
				name: 类的关联属性名
				cascade：级联关系  级联的新增与修改
				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 从表 的外键
				子标签one-to-many：
						class：外键对应的实体类
		 -->
		<bag lazy="false" name="orderItem" cascade="save-update" inverse="true" >
			<!-- 从表的外键 -->
			<key column="oid"></key>
			<one-to-many class="com.yz.three.entity.OrderItem"/>
		</bag>
	</class>

</hibernate-mapping>

订单项的配置文件orderItem.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.yz.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>
		<many-to-one name="order" class="com.yz.three.entity.Order" column="oid"></many-to-one>
	</class>
</hibernate-mapping>

有了配置文件必须得有实体类
order.java

package com.yz.three.entity;

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

public class Order {
	private Integer orderId;
	private String orderNo;
	private List<OrderItem> orderItem = new ArrayList<>();
	private Integer initChildren =0;//0是懒加载1：false
	
	
	
	
	public Integer getInitChildren() {
		return initChildren;
	}
	public void setInitChildren(Integer initChildren) {
		this.initChildren = initChildren;
	}
	//建立关联关系  一个订单对应多个订单想法
	public List<OrderItem> getOrderItem() {
		return orderItem;
	}
	public void setOrderItem(List<OrderItem> orderItem) {
		this.orderItem = orderItem;
	}
	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.java

package com.yz.three.entity;

public class OrderItem {
	private Integer orderItemId;
	private Integer productId;
	private Integer quantity;
	private Integer oid;
	private Order order;
	//建立关联关系  一个订单想对应的是一个订单
	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;
	}
	@Override
	public String toString() {
		return "OrderItem [orderItemId=" + orderItemId + ", productId=" + productId + ", quantity=" + quantity
				+ ", oid=" + oid + ", order=" + order + "]";
	}
	
	
	

}

做完这些基础之后我们写一个dao类
DemoDao.java

package com.yz.three.dao;

import java.util.List;

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

import com.yz.three.entity.Order;
import com.yz.three.entity.OrderItem;
import com.yz.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())) {
			Hibernate.initialize(o.getOrderItem());
			System.out.println(o.getOrderItem());
		}
		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.getOrderItem()) {
			session.delete(oi);
		}
		session.delete(order2);
//		session.delete(order);
		transaction.commit();
		session.close();
	}
	
	
}

因为dao类里面的需要实现的功能比较多所以我们再dao类的基础上给它加一个test类
如下图

就演变成了这个
DemoDaotest.java

package com.yz.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.yz.three.entity.Order;
import com.yz.three.entity.OrderItem;

/**
 * @Befores没测试一个test标记的测试方法，都会执行一次
 * @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 20190320
 *
 */

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("释放资源的");
	}
*/
	@Test
	public void testAddOrder() {
		Order order = new Order();
		order.setOrderNo("p2o");
		OrderItem orderItem =null;
		for (int i = 0; i < 6; i++) {
			orderItem = new OrderItem();
			orderItem.setProductId(10+i);
			orderItem.setQuantity(20+i);
			//维护关联关系
			orderItem.setOrder(order);
			order.getOrderItem().add(orderItem);
			
		}
		demodao.addOrder(order);
	}

	@Test
	public void testAddOrderItem() {
		OrderItem orderItem =null;
		for (int i = 0; i < 6; i++) {
			orderItem = new OrderItem();
			orderItem.setProductId(10+i);
			orderItem.setQuantity(20+i);
			//维护关联关系
			Order order = new Order();
			order.setOrderId(1);
			
			order.getOrderItem().add(orderItem);
			orderItem.setOrder(order);
			demodao.addOrderItem(orderItem);
			
		}
		
		
	}
		//当lazy=false的时候。会让hibernate执行两次操作，session才会关闭
		//反之为true时执行一次session就会关闭
		//从上面看lazy==false更好，但为什么默认为true
		//出于性能的考虑，所以hibernate3.0之后lazy这个属性，并让他默认为true，也就是说不加载关联属性
	@Test
	public void testGetOrder() {
		Order order = new  Order();
		order.setOrderId(1);
		order.setInitChildren(1);
		Order o = this.demodao.getOrder(order);
		List<OrderItem> orderItem1 = o.getOrderItem();
		for (OrderItem orderItem : orderItem1) {
			System.out.println(orderItem);
		}
		System.out.println(o);
	}

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

	@Test
	public void testDelOrder() {
		Order order = new  Order();
		order.setOrderId(1);
		this.demodao.delOrder(order);
	}

}

基本上就完成了这些功能