Hibernate一对多关系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:t_hibernate_ordert_hibernate_order_item一个订单对应多个订单项class Order{ private ListOrderItem orderItems; } class OrderItem{ private Order order; } class B{ private String name; } public class A{ private B b new B; public A(){} } hibernate:orm框架、以面向对象的思想操作数据库 实体类--》表 属性--》字段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 SetOrderItem OrderItems; } session.get(Order.class,1)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 lazytrue nameorderItems cascadesave-update inversetrue key columnoid/key one-to-many classcom.javaxl.three.entity.OrderItem / /set2.3 建立订单到客户的多对一关联关系!--1.注释 2.只读-- property namecid typejava.lang.Integer columncid insertfalse updatefalse /property2.4 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.实际案例4.1 项目整体结构DemoDaopackage com.su.three.entity; import java.util.List; import org.hibernate.Hibernate; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test; import com.su.two.util.SessionFactoryUtils; public class DemoDao { /** * 为了测试关系型映射文件配置准确 * 讲解insertfalseupdatefalse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 ListOrder getOrderList() { Session session SessionFactoryUtils.openSession(); Transaction transaction session.beginTransaction(); ListOrder 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(); } }DemoDaoTest package com.su.three.entity; import static org.junit.Assert.*; import java.util.List; import org.junit.Test; /** * author Administrator * */ public class DemoDaoTest { private DemoDao demoDaonew DemoDao(); Test public void testAddOrder() { Order ordernew Order(); order.setOrderNo(购物); for(int i0;i6;i) { OrderItem oinew OrderItem(); oi.setProductId(10i); oi.setQuantity(20i); // 绑定订单和订单子项的关系 order.getOrderItems().add(oi); oi.setOrder(order); } demoDao.addOrder(order); } Test public void testAddOrderItem() { OrderItem oinew OrderItem(); oi.setProductId(66); oi.setQuantity(66); Order ordernew Order(); order.setOrderId(11); oi.setOrder(order); demoDao.addOrderItem(oi); } Test public void testGetOrder() { Order ordernew Order(); order.setOrderId(11); order.setInitChildren(1); Order o demoDao.getOrder(order); System.out.println(o.getOrderNo()); //是否能拿到刚才添加的6条订单子项数据呢 /** * 如果将懒加载的功能关闭也就是lazyfalse, * 那么在查询多条订单数据的情况下是非常影响性能的 * 思考 * 查单个需要关闭懒加载 目的是需要加载出关联的数据 * 查多个不能关闭懒加载 加载关联表的数据的查询次数过多 * */ // org.hibernate.LazyInitializationException: // failed to lazily initialize a collection of role: com.wxm.three.entity.Order.orderItems, could not initialize proxy - no Session System.out.println(order.getOrderItems().size()); } Test public void testGetOrderList() { // 第一种低性能的做法 ListOrder orderListdemoDao.getOrderList(); for (Order order : orderList) { System.out.println(order.getOrderNo()); } } Test public void testDelOrder() { Order ordernew Order(); order.setOrderId(11); this.demoDao.delOrder(order); } }Orderpackage com.su.three.entity; import java.util.ArrayList; import java.util.List; public class Order { private Integer orderId; private String orderNo; private ListOrderItem orderItemsnew ArrayList() ; private Integer initChildren0;//0默认懒加载1强制加载 public Integer getInitChildren() { return initChildren; } public void setInitChildren(Integer initChildren) { this.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 ListOrderItem getOrderItems() { return orderItems; } public void setOrderItems(ListOrderItem orderItems) { this.orderItems orderItems; } }OrderItempackage com.su.three.entity; public class OrderItem { private Integer orderItemId; private Integer productId; private Integer quantity; private Integer oid; private 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; } public Order getOrder() { return order; } public void setOrder(Order order) { this.order order; } }Order.hbm.xml?xml version1.0 encodingUTF-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 namecom.su.three.entity.Order tablet_hibernate_order id nameorderId typejava.lang.Integer columnorder_id generator classincrement / /id property nameorderNo typejava.lang.String columnorder_no /property !-- bag标签 name :当前要映射的类的关联属性 cascade:维和关联关系 inverse:决定由谁来维护关系 key标签 column: 表的外键对应的列段 one-to-many : class:关键属性对应的类的全路径名 -- bag nameorderItems cascadesave-update inversetrue key columnoid/key one-to-many classcom.su.three.entity.OrderItem/one-to-many /bag /class /hibernate-mappingOrderItem.hbm.xml?xml version1.0 encodingUTF-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 namecom.su.three.entity.OrderItem tablet_hibernate_order_item id nameorderItemId typejava.lang.Integer columnorder_item_id generator classincrement / /id property nameproductId typejava.lang.Integer columnproduct_id /property property namequantity typejava.lang.Integer columnquantity /property property nameoid typejava.lang.Integer columnoid insertfalse updatefalse /property !-- many-to-one:多对一的配置 name:当前所要映射的类ordercom.su.three.entity.Order的order class:映射的类的全路径名映射的类 column:外键 -- many-to-one nameorder classcom.su.three.entity.Order columnoid/many-to-one /class /hibernate-mapping4.2 懒加载DemoDaoTestpackage com.su.three.entity; import static org.junit.Assert.*; import java.util.List; import org.junit.Test; public class DemoDaoTest { private DemoDao demoDaonew DemoDao(); Test public void testAddOrder() { Order ordernew Order(); order.setOrderNo(zmt购物); for(int i0;i6;i) { OrderItem oinew OrderItem(); oi.setProductId(10i); oi.setQuantity(20i); // 绑定订单和订单子项的关系 order.getOrderItems().add(oi); oi.setOrder(order); } demoDao.addOrder(order); } Test public void testAddOrderItem() { OrderItem oinew OrderItem(); oi.setProductId(66); oi.setQuantity(66); Order ordernew Order(); order.setOrderId(11); oi.setOrder(order); demoDao.addOrderItem(oi); } Test public void testGetOrder() { Order ordernew Order(); order.setOrderId(11); order.setInitChildren(1); Order o demoDao.getOrder(order); System.out.println(o.getOrderNo()); //是否能拿到刚才添加的6条订单子项数据呢 /** * 如果将懒加载的功能关闭也就是lazyfalse, * 那么在查询多条订单数据的情况下是非常影响性能的 * 思考 * 查单个需要关闭懒加载 目的是需要加载出关联的数据 * 查多个不能关闭懒加载 加载关联表的数据的查询次数过多 * */ // org.hibernate.LazyInitializationException: // failed to lazily initialize a collection of role: com.wxm.three.entity.Order.orderItems, could not initialize proxy - no Session System.out.println(order.getOrderItems().size()); } Test public void testGetOrderList() { // 第一种低性能的做法 ListOrder orderListdemoDao.getOrderList(); for (Order order : orderList) { System.out.println(order.getOrderNo()); } } Test public void testDelOrder() { Order ordernew Order(); order.setOrderId(11); this.demoDao.delOrder(order); } }运行结果新增删除