hibernate关联关系（一对多）
作者：互联网
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。例如:
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
新建实体类关联关系：Order
package com.zl.three.entity;
import java.util.ArrayList;
import java.util.List;
public class Order {
private Integer orderId;
private String orderNo;
//建立了关联关系 一个订单对应了多个订单项
private List<OrderItem> OrderItems = new ArrayList<>();
private Integer initChildren = 0;//懒加载
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 + "]";
}
}
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.zl.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：
lazy:是否懒加载，默认是懒加载的 true 懒汉模式
name:类的关联属性名
cascade:级联关系 级联新增与修改
inverse:关联关系交给对方控制 默认是true，当前类不维护关联关系
子标签key：
column：主表的主键 从表的外键
子标签one-to-many：
class:外键对应的实体类
-->
<bag lazy="false" name="orderItems" cascade="save-update" inverse="true" >
<key column="oid"></key>
<one-to-many class="com.zl.three.entity.OrderItem"/>
</bag>
</class>
</hibernate-mapping>
OrderItem
package com.zl.three.entity;
public class OrderItem {
private Integer orderItemId;
private Integer productId;
private Integer quantity;
private Integer oid;
//建立关联关系 一个订单项对应的是一个订单
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 + "]";
}
}
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.zl.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 name="order" class="com.zl.three.entity.Order" column="oid">
</many-to-one>
</class>
</hibernate-mapping>
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> <!-- 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/db_0601?useUnicode=true&characterEncoding=UTF-8 </property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <!-- <property name="dialect">org.hibernate.dialect.MySQLDialect</property> --> <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property> <property name="hbm2ddl.auto">update</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/zl/one/entity/User.hbm.xml" /> <!-- 主键生成策略 --> <mapping resource="com/zl/two/entity/Worker.hbm.xml" /> <mapping resource="com/zl/two/entity/Student.hbm.xml" /> <!-- 一对多 --> <mapping resource="com/zl/three/entity/OrderItem.hbm.xml" /> <mapping resource="com/zl/three/entity/Order.hbm.xml" /> </session-factory> </hibernate-configuration>
DemoDao
package com.zl.three.DemoDao;
import java.util.List;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.zl.three.entity.Order;
import com.zl.three.entity.OrderItem;
import com.zl.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())) {
// 强制加载关联对象
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;
}
/**
* 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();
}
}
利用Junit测试DemoDaoTest
package com.zl.three.DemoDao;
import java.util.List;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.zl.three.entity.Order;
import com.zl.three.entity.OrderItem;
/**
* @Before每测试一个@Test标记的测试方法，都会调用之前执行一次
* @After每测试一个@Test标记的测试方法，都会调用之后执行一次
* @author zl
*
*/
public class DemoDaoTest {
private DemoDao demoDao = new DemoDao();
/*@Before
public void setUp() throws Exception {
}
@After
public void tearDown() throws Exception {
}*/
@Test
public void testAddOrder() {
Order order = new Order();
order.setOrderNo("p20");
OrderItem orderItem = new OrderItem();
for (int i = 0; i < 6; i++) {
orderItem = new OrderItem();
orderItem.setProductId(10+i);
orderItem.setQuantity(20+i);
//维护关联关系
orderItem.setOrder(order);
order.getOrderItems().add(orderItem);
}
demoDao.addOrder(order);
}
@Test
public void testAddOrderItem() {
OrderItem orderItem = new OrderItem();
orderItem.setProductId(22);
orderItem.setQuantity(11);
Order order = new Order();
order.setOrderId(2);
order.getOrderItems().add(orderItem);
orderItem.setOrder(order );
demoDao.addOrderItem(orderItem);
}
@Test
public void testGetOrder() {
Order order = new Order();
order.setOrderId(1);
// order.setInitChildren(1);
Order order2 = this.demoDao.getOrder(order);
// 当lazy=false的时候，会让hibernate执行完两次操作，session才会关闭
//出于性能的考虑，所用hibernate3.0出现lazy这个属性，也就是说吧加载关联属性
// List<OrderItem> orderItems = order2.getOrderItems();
// for (OrderItem orderItem : orderItems) {
// System.out.println(orderItem);
// }
System.out.println(order2);
}
@Test
public void testGetOrderList() {
List<Order> orderList = this.demoDao.getOrderList();
for (Order order : orderList) {
for (OrderItem orderItem : order.getOrderItems()) {
System.out.println(orderItem);
}
System.out.println(order);
}
}
@Test
public void testDelOrder() {
Order order = new Order();
order.setOrderId(2);
this.demoDao.delOrder(order);
}
}
一对多的执行原理:
1.对hibernate.cfg.xml进行建模，等到sessionFactory对象
2.并且拿到了mapping resource里的内容
3.拿到了Order.hbm.xml配置文件
4.可以再次建模，拿到com.zl.three.entity.Order，以及t_hibernate_order
类属性，以及表列段
5.生成动态sql
执行sql最终得到meterData（源数据模型）
6.Order o1 = Class.forName("com.zl.three.entity.Order").newInstance(0);
o1.set...
...
最终得到：
List<Order> list=new arr..
list.add(o1);
..
最终list中所有order实例都有值了（这里只是处理表面的非外键列段，原理完全跟baseDao一样）
7.处理关联关系 orderitems oid com.zl.three.entity.OrderItem
通过one-to-many这个标签以及class对应的全路径名会找到对class对应的全路径名对应的专属映射文件
也就是找到了 OrderItem.hbm.xml,拿到他之后就可以拿到t_hibernate_order_item
8.select * from t_hibernate_order_item;
最终得到了一个List<OrderItem> ois
9.给order的关联关系属性赋值
List<Order> list=new arr..
for(Order o:list){
o.setOrderItem(ois);
}
标签：hibernate,orderItem,关联,Order,order,session,Integer,一对,public 来源： https://www.cnblogs.com/BAYOUA/p/11299426.html