hibernate学习2之many-to-one

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);
    }
  }