在領(lǐng)域模型中，類與類之間最普遍的關(guān)系就是關(guān)聯(lián)關(guān)系在UML中，關(guān)聯(lián)是有方向的　　以Customer和Order為例：一個用戶能發(fā)出多個訂單，而一個訂單只能屬于一個客戶。從Order到Customer的關(guān)聯(lián)是多對一關(guān)聯(lián)；而從Customer到Order是一對多關(guān)聯(lián)單向n-1　　單向n-1關(guān)聯(lián)只需從n的一端可以訪問到1的一端　　域模型：從Order到Customer的多對一單向關(guān)聯(lián)需要在Order類中定義一個Customer屬性，而在Customer類中無需定義存放Order對象的集合屬性　　關(guān)系數(shù)據(jù)模型：ORDER表中的CUSTOMER_ID參照CUSTOMER表的主鍵

代碼如下：

 1 package com.yl.hibernate.entities.n21; 2  3 public class Customer { 4      5     PRivate Integer customerId; 6     private String customerName; 7     public Integer getCustomerId() { 8         return customerId; 9     }10     public void setCustomerId(Integer customerId) {11         this.customerId = customerId;12     }13     public String getCustomerName() {14         return customerName;15     }16     public void setCustomerName(String customerName) {17         this.customerName = customerName;18     }19     20     21 }

 1 package com.yl.hibernate.entities.n21; 2  3 public class Order { 4      5     private Integer orderId; 6     private String orderName; 7      8     private Customer customer; 9 10     public Integer getOrderId() {11         return orderId;12     }13 14     public void setOrderId(Integer orderId) {15         this.orderId = orderId;16     }17 18     public String getOrderName() {19         return orderName;20     }21 22     public void setOrderName(String orderName) {23         this.orderName = orderName;24     }25 26     public Customer getCustomer() {27         return customer;28     }29 30     public void setCustomer(Customer customer) {31         this.customer = customer;32     }33     34     35 }

Customer.hbm.xml

 1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2014-11-26 19:19:40 by Hibernate Tools 3.4.0.CR1 --> 5 <hibernate-mapping> 6     <class name="com.yl.hibernate.entities.n21.Customer" table="CUSTOMERS"> 7         <id name="customerId" type="java.lang.Integer"> 8             <column name="CUSTOMER_ID" /> 9             <generator class="native" />10         </id>11         <property name="customerName" type="java.lang.String">12             <column name="CUSTOMER_NAME" />13         </property>14     </class>15 </hibernate-mapping>

Order.hbm.xml

 1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2014-11-26 19:19:40 by Hibernate Tools 3.4.0.CR1 --> 5 <hibernate-mapping> 6     <class name="com.yl.hibernate.entities.n21.Order" table="ORDERS"> 7         <id name="orderId" type="java.lang.Integer"> 8             <column name="ORDER_ID" /> 9             <generator class="native" />10         </id>11         <property name="orderName" type="java.lang.String">12             <column name="ORDER_NAME" />13         </property>14         <!-- 映射多對一的映射關(guān)系。使用many-to-one 來映射多對一的關(guān)聯(lián)關(guān)系15             name：多這一端關(guān)聯(lián)的一那一端的屬性的名字16             class：一那一端的屬性對應(yīng)的類名17             column：一那一端在多的一端對應(yīng)的數(shù)據(jù)表中的外鍵的名字18          -->19         <many-to-one name="customer" class="com.yl.hibernate.entities.n21.Customer" column="CUSTOMER_ID">20         </many-to-one>21        22     </class>23 </hibernate-mapping>

測試類：

  1 package com.yl.hibernate.entities.n21;  2   3   4 import org.hibernate.session;  5 import org.hibernate.SessionFactory;  6 import org.hibernate.Transaction;  7 import org.hibernate.cfg.Configuration;  8 import org.hibernate.service.ServiceRegistry;  9 import org.hibernate.service.ServiceRegistryBuilder; 10 import org.junit.After; 11 import org.junit.Before; 12 import org.junit.Test; 13  14 public class HibernateTest { 15  16     private SessionFactory sessionFactory; 17     private Session session; 18     private Transaction transaction; 19      20     @Before 21     public void init() { 22         Configuration configuration = new Configuration().configure(); 23         ServiceRegistry serviceRegistry =  24                 new ServiceRegistryBuilder().applySettings(configuration.getProperties()) 25                                             .buildServiceRegistry(); 26  27         sessionFactory = configuration.buildSessionFactory(serviceRegistry); 28          29         session = sessionFactory.openSession(); 30  31         transaction = session.beginTransaction(); 32     } 33     @After 34     public void destory() { 35         transaction.commit(); 36          37         session.close(); 38          39         sessionFactory.close(); 40     } 41      42     @Test 43     public void testMany2OneSave() { 44         Customer customer = new Customer(); 45         customer.setCustomerName("BB"); 46          47         Order order1 = new Order(); 48         order1.setOrderName("ORDER-3"); 49          50         Order order2 = new Order(); 51         order2.setOrderName("ORDER-4"); 52          53         //設(shè)定關(guān)聯(lián)關(guān)系 54         order1.setCustomer(customer); 55         order2.setCustomer(customer); 56          57         //執(zhí)行save操作：先插入Customer，再插入Order，3條INSERT 58         //先插入1的一端，再插入n的一端，只有INSERT語句 59         /*session.save(customer); 60          61         session.save(order1); 62         session.save(order2);*/ 63          64         //先插入Order，在插入Customer. 3條INSERT, 2條UPDATE 65         //先插入n的一端，再插入1的一端，會多出UPDATE語句 66         //因為在插入多的一端時，無法確定1的一端的外鍵值，所以只能等1的一端插入后，在額外發(fā)送UPDATE語句 67         //推薦先插入1的一端，再插入n的一端 68         session.save(order1); 69         session.save(order2); 70          71         session.save(customer); 72     } 73      74     @Test 75     public void testMany2OneGet() { 76         //1.若查詢多的一端的一個對象，則默認(rèn)情況下，只查詢了多的一端的對象，而沒有查詢關(guān)聯(lián)的1的那一端的對象！ 77         Order order = (Order) session.get(Order.class, 2); 78         System.out.println(order.getOrderName()); 79         //2.在需要使用到關(guān)聯(lián)的對象時，才發(fā)送對應(yīng)的SQL語句 80         Customer customer = order.getCustomer(); 81         System.out.println(customer.getCustomerName()); 82          83         //3.在查詢Customer對象時，由多的一端導(dǎo)航到1的一端時， 84         //若此時，session已被關(guān)閉，則默認(rèn)情況下 85         //會發(fā)生懶加載異常 86          87         //4.獲取Order對象時，默認(rèn)情況下，其關(guān)聯(lián)的Customer對象時一個代理對象！ 88     } 89      90     @Test 91     public void testUpdate() { 92         Order order = (Order) session.get(Order.class, 2); 93         order.getCustomer().setCustomerName("AAA"); 94     } 95      96     @Test 97     public void testDelete() { 98         //在不設(shè)定級聯(lián)關(guān)系的情況下，且1這一端的對象有 n 的對象在引用， 則不能直接刪除1這一端的對象 99         Customer customer = (Customer) session.get(Customer.class, 1);100         session.delete(customer);101     }102     103     104     105 }