hibernate学习2之many-to-one

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public class Group {private int id;private String name;//setter,getter}

public class User {private int id;private String name;private Group group;//多个用户对应一个组       //setter,getter}

Group.hbm.xml:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping><class name="com.bjsxt.hibernate.Group" table="t_group"><id name="id"><generator class="native"/></id><property name="name"/></class></hibernate-mapping>

User.hbm.xml:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping><class name="com.bjsxt.hibernate.User" table="t_user"><id name="id"><generator class="native"/></id><property name="name"/><many-to-one name="group" column="groupid" cascade="all"/></class></hibernate-mapping>

hibernate.cfg.xml

<!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><hibernate-configuration><session-factory><property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_many2one</property><property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property><property name="hibernate.connection.username">root</property><property name="hibernate.connection.password">bjsxt</property><property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property><property name="hibernate.show_sql">true</property><mapping resource="com/bjsxt/hibernate/User.hbm.xml"/><mapping resource="com/bjsxt/hibernate/Group.hbm.xml"/></session-factory></hibernate-configuration>

测试一下：

public void testSave() {Session session = null;try {session = HibernateUtils.getSession();session.beginTransaction();Group group = new Group();group.setName("尚学堂");User user1 = new User();user1.setName("菜10");user1.setGroup(group);User user2 = new User();user2.setName("容祖儿");user2.setGroup(group);//不会抛出异常，因为User.hbm.xml中采用了cascade（级联）属性，它会在保存User前先保存Group（这样就用不着显式的调用session.save(group);）//采用cascade属性是解决TransientObjectException异常的一种手段session.save(user1);session.save(user2);session.getTransaction().commit();}catch(Exception e) {e.printStackTrace();session.getTransaction().rollback();}finally {HibernateUtils.closeSession(session);}}

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