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);