hibernate关联关系（一对多）

什么是关联(association)
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。

案例:如何建立客户和订单一对多双向关联
先不建立客户和订单的关联关系,定义实体及映射文件,单独执行保存操作
建立客户到订单的一对多关联关系

实例代码：

Order.java：

package com.entity;

import java.util.ArrayList;

import java.util.List;

public class Order {

	private Integer orderId;

	private String orderNo;

	private List<OrderItem> OrderItems=new ArrayList<>();

	private Integer initChildren=1;//1代表开启懒加载 0则关闭

 	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) {

		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 + "]";

	}

	public Order(Integer orderId, String orderNo) {

		super();

		this.orderId = orderId;

		this.orderNo = orderNo;

	}

	public Order() {

		super();

	}

}

OrderItem.java:

package com.entity;

public class OrderItem {

	private Integer orderItemId;

	private Integer productId;

	private Integer quantity;

	private Integer oid;

	private Order Order;

	public Order getOrder() {

		return Order;

	}

	public void setOrder(Order order) {

		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 + ", 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();

	}

}

　　在同包下导入Order.hbm.xml文件以及OrderItem.hbm.xml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.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  name="orderItems" inverse="true"  cascade="save-update" >

		  <!-- 从表的外键 -->

			<key column="oid"></key>

			<!-- 查询从表数据	 -->

			<one-to-many class="com.entity.OrderItem" />

		</bag>

	</class>

</hibernate-mapping>

　　OrderItme.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.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.entity.Order" column="oid">

		</many-to-one>

	</class>

</hibernate-mapping>

　　在hibernate.hbm.xml中进行配置

<?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/mysql?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/entity/user.hbm.xml" />

		<!-- 主键生成策略 -->

		<mapping resource="com/entity/Worker.hbm.xml" />

		<mapping resource="com/entity/Student.hbm.xml" />

		<!-- 关联关系 -->

		<mapping resource="com/entity/Order.hbm.xml" />

		<mapping resource="com/entity/OrderItem.hbm.xml" />

	</session-factory>

</hibernate-configuration>

　　DemoDao:

package com.dao;

import java.util.List;

import org.hibernate.Hibernate;

import org.hibernate.Session;

import org.hibernate.Transaction;

import com.entity.Order;

import com.entity.OrderItem;

import com.entity.Student;

import com.entity.Worker;

import com.util.SessionFactoryUtils;

/**

 * hibernate中的主键生成策略

 * 1、人工控制

 * 2、数据库控制

 * 3、hibernate控制

 * 4、自定义主键生成策略

 * @author xyls

 *

 */

public class DemoDao {

/**

 * 新增学生

 * @param stu

 */

	public void add(Student stu) {

		Session session = SessionFactoryUtils.openSession();

		Transaction transation=session.beginTransaction();

		session.save(stu);

		transation.commit();

		SessionFactoryUtils.closeSession();

	}

	/**

	 * 新增工人

	 * @param worker

	 */

	public void addWorker(Worker worker) {

		Session session = SessionFactoryUtils.openSession();

		Transaction transation=session.beginTransaction();

		session.save(worker);

		transation.commit();

		SessionFactoryUtils.closeSession();

	}

	/**

	 *

	 * @param args

	 */

	public static void testStudent() {

		DemoDao dao=new DemoDao();

		Student stu=new Student();

		stu.setSname("柳长歌");

		stu.setSid(97);

		dao.add(stu);

	}

	public static void main(String[] args) {

		DemoDao dao=new DemoDao();

		Worker worker=new Worker();

		worker.setWname("220");

		dao.addWorker(worker);

	}

	/**

	 * 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.getInitChildren())) {

			//0代表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;

	}

	/**

	 * 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();

	}

}

　　进行测试：

DemoDaoTest.java:

package com.dao;

import static org.junit.Assert.*;

import java.util.List;

import org.junit.Test;

import com.entity.Order;

import com.entity.OrderItem;

import com.test.delDemo;

public class DemoDaoTest {

	private DemoDao demoDao=new DemoDao();

	@Test

	public void testAddOrder() {

		Order order=new Order();

		order.setOrderNo("1001");

		OrderItem oi=null;

		for (int i = 0; i < 4; i++) {

			oi=new OrderItem();

			oi.setProductId(100+i);

			oi.setQuantity(200+i);

			oi.setOrder(order);

			order.getOrderItems().add(oi);

		}

		demoDao.addOrder(order);

//		demoDao.addOrderItem(orderItem);

	}

	@Test

	public void testAddOrderItem() {

		Order order=new Order();

		order.setOrderId(5);

		OrderItem oi=null;

		for (int i = 0; i < 4; i++) {

			oi=new OrderItem();

			oi.setProductId(100+i);

			oi.setQuantity(200+i);

			oi.setOrder(order);

			order.getOrderItems().add(oi);

			demoDao.addOrderItem(oi);

		}

	}

	@Test

	public void testGetOrder() {

		Order order=new Order();

		order.setOrderId(10);
　　　　　　//关闭懒加载

		order.setInitChildren(0);

		Order o=this.demoDao.getOrder(order);

		System.out.println(o.getOrderNo());

		System.out.println(o.getOrderItems());

	}

/**

 * 查单个需要关闭懒加载

 * 查多个不能关闭懒加载

 */

	@Test

	public void testGetOrderList() {

		List<Order> orderList= this.demoDao.getOrderList();

			for (Order order : orderList) {

				System.out.println(order.getOrderNo());

			//	System.out.println(order.getOrderItems());

			}

	}

	@Test

	public void testDelOrder() {

		Order order=new Order();

		order.setOrderId(9);

		this.demoDao.delOrder(order);

	}

}

结果：

testAddOrder：

Order表

OrderItem表：

testAddOrderItem:

testGetOrder:

testGetOrderList:

testDelOrder:

主表的oid为5的数据删除以及从表oid为5的数据也被删除

关于hibernate的懒加载：

如果说将懒加载的功能关闭，也就是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

所以我在Order.java中加入：

private Integer initChildren=1;（1代表开启懒加载 0则关闭）
在测试类中的用法：

关闭懒加载

		order.setInitChildren(0);

巴特西

hibernate关联关系（一对多）

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