hibernate一对多的关系
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。例如:
class B{
private String name;
}
public class A{
private B b = new B;
public A(){}
}
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
案例展示
- 先写好实体类
Order
package com.xfz.three.entity;
import java.util.ArrayList;
import java.util.List;
public class Order {
private Integer orderId;
private String orderNo;
private List orderItems=new ArrayList<>();
private Integer inintChildren=0;//0表示默认加载，1代表强制加载
public Integer getInintChildren() {
return inintChildren;
}
public void setInintChildren(Integer inintChildren) {
this.inintChildren = inintChildren;
}
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 getOrderItems() {
return orderItems;
}
public void setOrderItems(List orderItems) {
this.orderItems = orderItems;
}
@Override
public String toString() {
return "Order [orderId=" + orderId + ", orderNo=" + orderNo + ", orderItems=" + orderItems + "]";
}
}
OrderItem
package com.xfz.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;
}
@Override
public String toString() {
return "OrderItem [orderItemId=" + orderItemId + ", productId=" + productId + ", quantity=" + quantity
+ ", oid=" + oid + "]";
}
}
- 再写好实体类的映射文件
Order
OrderItem
- 导入所写好的dao方法
package com.xfz.three.dao;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.xfz.three.entity.Order;
import com.xfz.three.entity.OrderItem;
import com.xfz.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 getOrderList() {
Session session = SessionFactoryUtils.openSession();
Transaction transaction = session.beginTransaction();
List 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();
}
}
- 在核心配置文件中配置
root
123
jdbc:mysql://localhost:3306/mysql?useUnicode=true&characterEncoding=UTF-8
com.mysql.jdbc.Driver
org.hibernate.dialect.MySQLDialect
thread
true
true
- 最后开始测试demodao中的方法
package com.xfz.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.xfz.three.entity.Order;
import com.xfz.three.entity.OrderItem;
public class DemoDaoTest {
private DemoDao demoDao=new DemoDao();
@Test
public void testAddOrder() {
Order order=new Order();
order.setOrderNo("购物~");
for (int i = 0; i < 6; i++) {
OrderItem oi=new OrderItem();
oi.setProductId(10+i);
oi.setQuantity(20+i);
//之前用法
// demoDao.addOrderItem(oi);
order.getOrderItems().add(oi);
oi.setOrder(order);
}
demoDao.addOrder(order);
}
@Test
public void testAddOrderItem() {
OrderItem oi=new OrderItem();
oi.setProductId(66);
oi.setQuantity(66);
Order order=new Order();
order.setOrderId(11);
oi.setOrder(order);
demoDao.addOrderItem(oi);
}
@Test
public void testGetOrder() {
Order order=new Order();
order.setOrderId(11);
order.setInintChildren(1);
Order o=demoDao.getOrder(order);
//failed to lazily initialize a collection of role:
//com.xfz.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 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);
}
}
懒加载
懒加载失败错误：
//failed to lazily initialize a collection of role:
//com.xfz.three.entity.Order.orderItems, could not initialize proxy - no Session
解决方式：
一种是在bag标签中添加 lazy=“false” 属性。得到的结果虽然不报错但是会加载7条sql语句。弊端：性能太差，不推荐
另一种是强制加载，在订单中设置initchildren=0的字段，而0代表懒加载，1代表强制加载。在测试方法中设置initchildren为1，便可以解决问题
order.setInintChildren(1);
测试效果展示
新增的效果
删除后的效果
