1、一对多的关联配置
数据库：主表从表，通过外键关联
类：
Class A{
B b=new B();
}
Class B{
}
2.懒加载
3.一对多的自关联
4.多对多的关联
一、一对多的关联配置 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。
2、一对多的关联：例如：订单和订单项，一个订单有多个订单项；
但是一个订单项只有一个订单；
3、创建实体类和映射文件①、实体类：
（1）Order
package com.mwy.entity;
import java.util.HashSet;
import java.util.Set;
public class Order {
// create table t_hibernate_order
// (
// order_id int primary key auto_increment,
// order_no varchar(50) not null
// );
private Integer orderId;
private String orderNo;
//注意：变量属性一定用接口进行接受
private Set orderItems = new HashSet<>();
private Integer initOrderItems = 0;//0代表懒加载，1代表强制加载
public Integer getInitOrderItems() {
return initOrderItems;
}
public void setInitOrderItems(Integer initOrderItems) {
this.initOrderItems = initOrderItems;
}
public Set getOrderItems() {
return orderItems;
}
public void setOrderItems(Set orderItems) {
this.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;
}
}
（2）OrderItem
package com.mwy.entity;
public class OrderItem {
// 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)
// );
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;
}
}
②、映射文件：
（1）Order.hbm.xml
（2）OrderItem.hbm.xml
核心配置文件
工具类;
package com.mwy.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class SessionFactoryUtil {
static SessionFactory sessionFactory;
static {
Configuration configure = new Configuration().configure("hibernate.cfg.xml");
sessionFactory = configure.buildSessionFactory();
}
public static Session getSession() {
Session session = sessionFactory.getCurrentSession();
if(session == null) {
session = sessionFactory.openSession();
}
return session;
}
public static void main(String[] args) {
Session session = SessionFactoryUtil.getSession();
// Calling method 'isConnected' is not valid without an active transaction (Current status: NOT_ACTIVE)
session.beginTransaction();
System.out.println(session.isConnected());
session.close();
System.out.println(session.isConnected());
}
}
4、dao层
①、OrderDao
package com.mwy.dao;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.mwy.entity.Order;
import com.mwy.entity.OrderItem;
import com.mwy.util.SessionFactoryUtil;
public class OrderDao {
//查询
public Order get(Order order) {
Session session = SessionFactoryUtil.getSession();
Transaction transaction = session.beginTransaction();
Order o = session.get(Order.class, order.getOrderId());
// 并且想要查询出关联的订单项的数据是，采用强制加载
if(o != null && new Integer(1).equals(order.getInitOrderItems())) {
Hibernate.initialize(o.getOrderItems());
}
transaction.commit();
session.close();
return o;
}
//查询所有
public List list() {
Session session = SessionFactoryUtil.getSession();
Transaction transaction = session.beginTransaction();
List list = session.createQuery("from Order").list();
for (Order o: list) {
Hibernate.initialize(o.getOrderItems());
}
transaction.commit();
session.close();
return list;
}
//删除
public void delete(Order order) {
Session session = SessionFactoryUtil.getSession();
Transaction transaction = session.beginTransaction();
Order o = session.get(Order.class, order.getOrderId());
for(OrderItem oi:o.getOrderItems()) {
session.delete(oi);
}
session.delete(o);
transaction.commit();
session.close();
}
}
②、OrderItemDao
package com.mwy.dao;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.mwy.entity.OrderItem;
import com.mwy.util.SessionFactoryUtil;
public class OrderItemDao {
public OrderItem get(OrderItem orderItem) {
Session session = SessionFactoryUtil.getSession();
Transaction transaction = session.beginTransaction();
OrderItem oi = session.get(OrderItem.class, orderItem.getOrderItemId());
transaction.commit();
session.close();
return oi;
}
}
5、测试
package com.mwy.dao;
import java.util.List;
import org.junit.Test;
import com.mwy.entity.Order;
public class OrderDaoTest {
private OrderDao orderDao = new OrderDao();
@Test
public void testGet() {
Order order = new Order();
order.setOrderId(7);
// order.setInitOrderItems(1);
Order o = this.orderDao.get(order);
System.out.println(o.getOrderNo());
// System.out.println(o.getOrderItems());
}
@Test
public void testList() {
List list = this.orderDao.list();
for (Order o : list) {
System.out.println(o.getOrderNo());
// System.out.println(o.getOrderItems().size());
}
}
@Test
public void testDelete() {
Order order = new Order();
order.setOrderId(6);
this.orderDao.delete(order);
}
}
二、懒加载
1、测试
能查询到为7的订单
public void testGet() {
Order order = new Order();
order.setOrderId(7);
Order o = this.orderDao.get(order);
System.out.println(o.getOrderNo());
}
还没写完！！！！！！！！！！！！
