要点: 1.也就是有个主表,然后另外一个表引用主表中的某个字段作为外键
2.在副对象中,引用主表对象.然后在mapping文件中,映射多对一关系,并制定各自的属性名,类名,外键名
<!-- 映射多对一的关联关系。 使用 many-to-one 来映射多对一的关联关系 name: 多这一端:关联的一那一端的属性的名字 class: 一那一端:的属性对应的类名 column: 一那一端在多的一端对应的数据表中的外键的名字,可以随便取 <many-to-one name="customer" class="Customer"> <column name="CUSTOMER_ID" /> </many-to-one> 表名用了ORDER,使得出现了错误,改为ORDERS即可 Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER (ORDER_NAME, CUSTOMER_ID) values ('order1', 1)' at line 1 --> <many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one> package com.hgh.hibernate.nto1; public class Customer { private Integer customerId; private String customerName; public Integer getCustomerId() { return customerId; } public void setCustomerId(Integer customerId) { this.customerId = customerId; } public String getCustomerName() { return customerName; } public void setCustomerName(String customerName) { this.customerName = customerName; } } package com.hgh.hibernate.nto1; public class Order1 { private Integer orderId; private String orderName; private Customer customer; public Integer getOrderId() { return orderId; } public void setOrderId(Integer orderId) { this.orderId = orderId; } public String getOrderName() { return orderName; } public void setOrderName(String orderName) { this.orderName = orderName; } public Customer getCustomer() { return customer; } public void setCustomer(Customer customer) { this.customer = customer; } } <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2017-4-13 11:17:27 by Hibernate Tools 3.4.0.CR1 --> <hibernate-mapping package="com.hgh.hibernate.nto1"> <class name="Order1" table="ORDERS"> <id name="orderId" type="java.lang.Integer"> <column name="ORDER_ID" /> <generator class="native" /> </id> <property name="orderName" type="java.lang.String"> <column name="ORDER_NAME" /> </property> <!-- 映射多对一的关联关系。 使用 many-to-one 来映射多对一的关联关系 name: 多这一端:关联的一那一端的属性的名字 class: 一那一端:的属性对应的类名 column: 一那一端在多的一端对应的数据表中的外键的名字,可以随便取 <many-to-one name="customer" class="Customer"> <column name="CUSTOMER_ID" /> </many-to-one> 表名用了ORDER,使得出现了错误,改为ORDERS即可 Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER (ORDER_NAME, CUSTOMER_ID) values ('order1', 1)' at line 1 --> <many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one> </class> </hibernate-mapping> <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2017-4-13 11:17:27 by Hibernate Tools 3.4.0.CR1 --> <hibernate-mapping> <class name="com.hgh.hibernate.nto1.Customer" table="CUSTOMER"> <id name="customerId" type="java.lang.Integer"> <column name="CUSTOMER_ID" /> <generator class="native" /> </id> <property name="customerName" type="java.lang.String"> <column name="CUSTOMER_NAME" /> </property> </class> </hibernate-mapping> package com.hgh.hibernate.nto1; import static org.junit.Assert.*; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.InputStream; import java.io.OutputStream; import java.sql.Blob; import java.sql.Connection; import java.sql.SQLException; import java.util.Date; import org.hibernate.Hibernate; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; import org.hibernate.jdbc.Work; import org.hibernate.service.ServiceRegistry; import org.hibernate.service.ServiceRegistryBuilder; import org.junit.After; import org.junit.Before; import org.junit.Test; public class SessionTest { private SessionFactory SessionFactory; private ServiceRegistry ServiceRegistry; private Transaction transaction; private Session session; @Test public void testDelete(){ Customer customer = (Customer) session.get(Customer.class, 1); session.delete(customer); } @Test public void testUpdateManyToOne(){ Customer customer = (Customer) session.get(Customer.class, 1); customer.setCustomerName("313"); session.update(customer); } @Test public void testManyToOneGet(){ Order1 order1 = (Order1) session.get(Order1.class, 1); System.out.println(order1.getOrderName()); //com.hgh.hibernate.nto1.Customer_$$_javassist_3代理对象,需要使用的时候再填充 System.out.println(order1.getCustomer().getClass().getName()); Customer customer = order1.getCustomer(); //2. 在需要使用到关联的对象时, 才发送对应的 SQL 语句. System.out.println(customer.getCustomerName()); //3. 在查询 Customer 对象时, 由多的一端导航到 1 的一端时, //若此时 session 已被关闭, 则默认情况下 //会发生 LazyInitializationException 异常 //4. 获取 Order 对象时, 默认情况下, 其关联的 Customer 对象是一个代理对象! } @Test public void testNtoOne(){ Customer customer = new Customer(); customer.setCustomerName("customer2"); Order1 order = new Order1(); Order1 order2 = new Order1(); order.setOrderName("order33"); order2.setOrderName("order44"); order.setCustomer(customer); order2.setCustomer(customer); //执行 save 操作: 先插入 Customer, 再插入 Order, 3 条 INSERT //先插入 1 的一端, 再插入 n 的一端, 只有 INSERT 语句. // session.save(customer); // session.save(order); // session.save(order2); //先插入 Order, 再插入 Customer. 3 条 INSERT, 2 条 UPDATE //先插入 n 的一端, 再插入 1 的一端, 会多出 UPDATE 语句! //因为在插入多的一端时, 无法确定 1 的一端的外键值. 所以只能等 1 的一端插入后, 再额外发送 UPDATE 语句. //推荐先插入 1 的一端, 后插入 n 的一端 session.save(order); session.save(order2); session.save(customer); } @Before public void init(){ System.out.println("init"); Configuration configuration = new Configuration().configure(); ServiceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()) .buildServiceRegistry(); SessionFactory = configuration.buildSessionFactory(ServiceRegistry); session = SessionFactory.openSession(); transaction = session.beginTransaction(); } @After public void destroy(){ System.out.println("destroy"); transaction.commit(); session.close(); SessionFactory.close(); } }