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: 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 订单表、订单项表 select * from t_order t,t_orderItem m where t.oid = m.oid and ..... class Order{ private STIRNG OID; ... private Set<OrderItem> OrderItems; } session.get(Order.class,1)
#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 <set name="orders" inverse="true" cascade="save-update"> <key column="cid"></key> <one-to-many class="entity.Order"> </set> 2.3 建立订单到客户的多对一关联关系 <many-to-one name="customer" class="entity.Customer" column="cid"> <!--1.注释 2.只读--> <property name="cid" type="java.lang.Integer" column="cid" insert="false" update="false"> </property> 2.4 注意:在Hibernate当中定义实体对象的集合属性时,只能使用接口而不能使用类
#insert属性设置中主控方概念理解: 3. 以客户和订单的一对多双向关联为例,讲解Set元素中的cascade|inverse|outter-join|lazy属性作用 3.1 lazy:默认值为true,true延迟加载,false立即加载(一般设置为true,不使用立即加载,因为影响查询性能) 3.2 outter-join:默认值为false,true使用左外联接查询关联的(但一般不用，因为当我们把该属性设置为true时，所有的查询语句都会默认左外联，那样性能不高) 3.3 inverse:默认值为false,true表示将对方设置为主控方(一对多双向关联中一般将多方设置为主控方,这样可以减少SQL语句的数量,减少多余的操作) 3.4 cascade:用来控制如何操作关联的持久化对象的 3.4.1 none:保存，更新或删除当前对象时，忽略其它关联的对象 3.4.2 save-update:保存、更新时级联保存所有的临时对象，并且级联更新关联的游离对象 3.4.3 delete:通过session的delete方法删除当前对象，级联删除关联的对象 3.4.4 all:等于save-update操作+delete操作
小结： 多方的CRUD与没有建立关联关系之前的操作一致 一方的CRUD与没有建立关联关系之前的操作有变化 D：删除一方之前先删除多方 C：级联操作 R：代码控制多方
4. 案例:菜单对象的一对多双向自关联<!-- 多对一关系 -->
<!-- 多对一关系 --> <many-to-one name="order" class="com.company.four.entity.Order" column="oid" ></many-to-one>
<!-- cascade:用来维护实体类之间的关系所用 save-update可修改增加 inverse:关系是否由反方控制（是否由关联的表来控制） lazy:是否为懒加载（延迟加载） 性能不佳 --> <set name="orderItems" cascade="save-update" inverse="true"> <!-- 关联的表的id（外键） --> <key column="oid"></key> <!-- 定义一对多关系 --> <one-to-many class="com.company.four.entity.OrderItem"/> </set>
5. 如何将多方映射成一个有序的集合 <!-- bag元素可以映射List集合,order-by属性还可以用来排序(asc升序|desc降序)，其它和set元素的使用一样 --> <bag name="childMenus" inverse="true" lazy="true" outer-join="false" cascade="save-update" order-by="position asc"> <key column="super_menu_id"></key> <one-to-many class="entity.Menu" /> </bag> 核心 订单表、订单项
级联新增 外键处理的三种方式 1、删除从表对应的实体类中的外键属性 2、在配置的xml中外键属性上添加 insert=false，update=false的设置。 3、在配置的xml中的manyToOne标签中添加insert=false，update=false的设置。 级联新增 casecade=save-update 介绍
级联查询 配置文件介绍以及后台sql的形成过程 级联查询时的问题 Lazy=true介绍 查单个时存在问题 Lazy=false介绍 查所有时存在问题 解决方案：通过字段控制，强制加载。Hibernate.initialize()
普通删除 Order Add 讲外键的处理 Get/list order.getOrderItems.size讲懒加载的处理，sql形成过程 Del 将关系的处理中的删除
package com.company.four.dao;
import java.io.Serializable; import java.util.List; import java.util.Set;
import org.hibernate.Hibernate; import org.hibernate.Session; import org.hibernate.Transaction; import org.hibernate.query.Query;
import com.company.four.entity.Order; import com.company.four.entity.OrderItem; import com.company.two.util.SessionFactoryUtils;
public class OrderAction { public int save(Order order) { Session session = SessionFactoryUtils.getSession(); Transaction transaction = session.beginTransaction(); // Order order2 = session.get(Order.class, order.getOrderId()); session.save(order); transaction.commit(); session.close(); return order.getOrderId(); } public Integer addOrderItem(OrderItem orderItem) { Session session = SessionFactoryUtils.getSession(); Transaction transaction = session.beginTransaction(); Integer otid = (Integer) session.save(orderItem); transaction.commit(); session.close(); return otid; } public Integer addOrder(Order order) { Session session = SessionFactoryUtils.getSession(); Transaction transaction = session.beginTransaction(); Integer oid = (Integer) session.save(order); transaction.commit(); session.close(); return oid; } public Order getOrder(Order order) { Session session = SessionFactoryUtils.getSession(); Transaction transaction = session.beginTransaction(); Order order2 = session.get(Order.class, order.getOrderId()); //判断是否需要直接加载 if(order2 != null && new Integer(1).equals(order.getInitOrderItems())) { Hibernate.initialize(order2.getOrderItems()); } transaction.commit(); session.close(); return order2; } public List<Order> getOrderList() { Session session = SessionFactoryUtils.getSession(); Transaction transaction = session.beginTransaction(); List orderList = session.createQuery("from Order").list(); transaction.commit(); session.close(); return orderList; } public void delOrder(Order order) { Session session = SessionFactoryUtils.getSession(); Transaction transaction = session.beginTransaction(); Order order2 = session.get(Order.class, order.getOrderId()); Set<OrderItem> orderItems = order2.getOrderItems(); for (OrderItem oi : orderItems) { session.delete(oi); } session.delete(order2); transaction.commit(); session.close(); } }
package com.company.four.dao;
import java.util.HashSet; import java.util.List; import java.util.Set;
import org.junit.Before; import org.junit.Test;
import com.company.four.entity.Order; import com.company.four.entity.OrderItem;
public class OrderActionTest { OrderAction orderAction = new OrderAction();
@Before public void setUp() throws Exception { }
@Test public void testGet() { Order order = new Order(); int save = orderAction.save(order); System.out.println(save); } @Test public void addGet() { OrderItem orderItem = new OrderItem(); orderItem.setProduct_id(89); orderItem.setQuantity(78); //描述关系 Order order = new Order(); order.setOrderId(7); orderItem.setOrder(order); Integer addOrderItem = this.orderAction.addOrderItem(orderItem); System.out.println(addOrderItem); } @Test public void addOrder() { Order order = new Order(); order.setOrderNo("P8"); for (int i = 0; i < 6; i++) { OrderItem orderItem = new OrderItem(); orderItem.setProduct_id(i); orderItem.setQuantity(i); //双向关联关系 order.getOrderItems().add(orderItem); orderItem.setOrder(order); } Integer addOrder = this.orderAction.addOrder(order); System.out.println(addOrder); } @Test public void addOrdera() { Order order = new Order(); order.setOrderNo("P12"); Set<OrderItem> hashSet = new HashSet<>(); for (int i = 0; i < 6; i++) { OrderItem orderItem = new OrderItem(); orderItem.setProduct_id(i); orderItem.setQuantity(i); //双向关联关系 orderItem.setOrder(order); hashSet.add(orderItem); } order.setOrderItems(hashSet); Integer addOrder = this.orderAction.addOrder(order); System.out.println(addOrder); } @Test public void getOrder() { // could not initialize proxy 懒加载 Order order = new Order(); order.setOrderId(8); //设置为非懒加载 order.setInitOrderItems(1); Order order2 = this.orderAction.getOrder(order); System.out.println(order2.getOrderNo()); System.out.println(order2.getOrderItems().getClass().getName()); Set<OrderItem> orderItems = order2.getOrderItems(); for (OrderItem o : orderItems) { System.out.println(o.getOrderItemId()); } } @Test public void getOrderList() { List<Order> orderList = this.orderAction.getOrderList(); for (Order order : orderList) { System.out.println(order.getOrderNo()); Set<OrderItem> orderItems = order.getOrderItems(); for (OrderItem o : orderItems) { System.out.println(o.getOrderItemId()); } } } @Test public void DelOrder() { Order order = new Order(); order.setOrderId(11); this.orderAction.delOrder(order); }
}
package com.company.four.entity;
import java.util.HashSet; import java.util.Set;
public class Order { private Integer orderId; private String orderNo; //定义一对多的关系时一定要采用接口的方式，不能用实现类（用set，不能用hashset） private Set<OrderItem> orderItems = new HashSet<>(); private Integer initOrderItems = 0;//0代表懒加载 1代表立即加载 public Integer getInitOrderItems() { return initOrderItems; } public void setInitOrderItems(Integer initOrderItems) { this.initOrderItems = initOrderItems; } public Set<OrderItem> getOrderItems() { return orderItems; } public void setOrderItems(Set<OrderItem> 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; } }
package com.company.four.entity;
public class OrderItem { private Integer orderItemId; private Integer product_id; private Integer quantity; private Integer oid; //一对一 private Order order = new 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 getProduct_id() { return product_id; } public void setProduct_id(Integer product_id) { this.product_id = product_id; } 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; } }
