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Hibernate一对多

一、介绍

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。
#关键点都在数据库中的外键上面,请好好理解下面这二句SQL和一对多及多对一的关系
#select * from Orders where cid=? //这条SQL返回客户对应的0-n个订单
#select * from Customers where customerId=? //这条SQL返回订单对应的1个客户
#通过这二条SQL不难看出,外键在这里有二个用途:查找客户的订单,查找订单对应的客户
2. 案例:如何建立客户和订单一对多双向关联
2.1 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
2.2 建立客户到订单的一对多关联关系

项目展示：

二、代码显示：
entity包
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.DZY.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 name:当前要映射的类的关联属性 cascade:维护关联关系 inverse:决定由谁来维护关联关系 key标签 column:表的外键对应的列段 one-to-many: class:关联属性对应的类的全路径名 --> <bag name="orderItems" cascade="save-update" inverse="true"> <key column="oid"></key> <one-to-many class="com.DZY.three.entity.OrderItem" /> </bag> </class> </hibernate-mapping>

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.DZY.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:多对一的配置（因为多个订单对应一个 订单 name:指的是当前所要映射的类com.DZY.three.entity.OrderItem的关联属性order Class:指的是关联属性的类别(全路径名） column:这里填的是外键； --> <many-to-one name="order" class="com.DZY.three.entity.Order" column="oid"></many-to-one> </class> </hibernate-mapping>

Order

package com.DZY.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 InitChildren=0;//0代表默认懒加载，1代表强制加载 public Integer getInitChildren() { return InitChildren; } public void setInitChildren(Integer initChildren) { InitChildren = initChildren; } 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; } @Override public String toString() { return "Order [orderId=" + orderId + ", orderNo=" + orderNo + ", orderItems=" + orderItems + "]"; } }

OrderItem

package com.DZY.three.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) { 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; } }

dao包
DemoDao

package com.DZY.three.dao; import java.util.List; import org.hibernate.Hibernate; import org.hibernate.Session; import org.hibernate.Transaction; import com.DZY.three.entity.Order; import com.DZY.three.entity.OrderItem; import com.DZY.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.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(); } }

SessionFactoryUtils;这个类需要话在我上一个作品里。
上一个作品https://blog.csdn.net/qq_44224029/article/details/100152078
通过JUnit Test case 获得下面个类。不懂怎么获取去看。

DemoDaoTest

package com.DZY.three.dao; import static org.junit.Assert.*; import java.util.ArrayList; import java.util.List; import org.junit.Test; import com.DZY.three.entity.Order; import com.DZY.three.entity.OrderItem; public class DemoDaoTest { private DemoDao demoDao = new DemoDao(); @Test public void testAddOrder() { Order order = new Order(); order.setOrderNo("DZY"); for (int i = 0; i < 6; i++) { OrderItem oi = new OrderItem(); oi.setProductId(10 + i); oi.setQuantity(20 + i); // demoDao.addOrderItem(oi) order.getOrderItems().add(oi); oi.setOrder(order); } demoDao.addOrder(order); } @Test public void testAddOrderItem() { OrderItem oi = new OrderItem(); oi.setProductId(55); oi.setQuantity(55); Order order = new Order(); order.setOrderId(11); oi.setOrder(order); demoDao.addOrderItem(oi); } /** * 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） */ @Test public void testGetOrder() { Order order = new Order(); order.setOrderId(11); order.setInitChildren(1); Order o=demoDao.getOrder(order); //failed to lazily initialize a collection of role: com.DZY.three.entity.Order.orderItems //could not initialize proxy - no Session System.out.println(o.getOrderNo()); System.out.println(o.getOrderItems().size()); } @Test public void testGetOrderList() { List<Order> orderList=demoDao.getOrderList(); for (Order order : orderList) { System.out.println(order.getOrderNo()); // System.out.println(order.getOrderItems().size()); } } @Test public void testDelOrder() { Order order = new Order(); order.setOrderId(11); this.demoDao.delOrder(order); } }

配置
hibernate.cfg.xml

<?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> <!--一对多 --> <mapping resource="com/DZY/three/entity/Order.hbm.xml" /> <mapping resource="com/DZY/three/entity/OrderItem.hbm.xml" /> </session-factory> </hibernate-configuration>

三、操作DemoDaoTest

注意：Orderltem.hbm.xml
图片黄色地方。如果没有加上。就会报下面的错误。

1.增加；

public void testAddOrder() { Order order = new Order(); order.setOrderNo("DZY"); for (int i = 0; i < 6; i++) { OrderItem oi = new OrderItem(); oi.setProductId(10 + i); oi.setQuantity(20 + i); // demoDao.addOrderItem(oi) order.getOrderItems().add(oi); oi.setOrder(order); } demoDao.addOrder(order); }

显示结果：

增加订单

public void testAddOrderItem() { OrderItem oi = new OrderItem(); oi.setProductId(55); oi.setQuantity(55); Order order = new Order(); order.setOrderId(11); oi.setOrder(order); demoDao.addOrderItem(oi); }

显示结果：

获得单个数据会包错，不推荐这个方法
在order.xml

lazy="false" 懒加载开始为true 改为false <bag lazy="false" name="orderItems" cascade="save-update" inverse="true">

能起效，但是会增加运行速度

在DemoDao

public Order getOrder(Order order) { Session session = SessionFactoryUtils.openSession(); Transaction transaction = session.beginTransaction(); Order o = session.get(Order.class, order.getOrderId()); //获得单个数据 。InitChildren这个需要在order定义 if(o != null && new Integer(1).equals(order.getInitChildren())) { Hibernate.initialize(o.getOrderItems()); // System.out.println(o.getOrderItems()); } transaction.commit(); session.close(); return o; }

3.获得单个数据

public void testGetOrder() { Order order = new Order(); order.setOrderId(12); order.setInitChildren(1); Order o=demoDao.getOrder(order); //failed to lazily initialize a collection of role: com.DZY.three.entity.Order.orderItems //could not initialize proxy - no Session System.out.println(o.getOrderNo()); // System.out.println(o.getOrderItems().size()); }

显示结果

4.查询全部

public void testGetOrderList() { List<Order> orderList=demoDao.getOrderList(); for (Order order : orderList) { System.out.println(order.getOrderNo()); // System.out.println(order.getOrderItems().size()); } }

显示结果

5.删除

public void testDelOrder() { Order order = new Order(); order.setOrderId(11); this.demoDao.delOrder(order); }