04hibernate_many2one_cascade

package com.bjsxt.hibernate;

import org.hibernate.Session;

import junit.framework.TestCase;

public class Many2OneTest extends TestCase {
    //忘记存一方对象group，再存多方对象user，因为多方对象user中有一个字段groupid要参考一方对象，所以会抛出异常
    public void testSave1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            Group group = new Group();
            group.setName("尚学堂");
            
            User user1 = new User();
            user1.setName("猪八戒");
            user1.setGroup(group);
            
            User user2 = new User();
            user2.setName("七仙女");
            user2.setGroup(group);
            
            //不能成功保存，抛出TransientObjectException异常
            //因为Group为Transient状态，oid没有分配值
            //persistent状态的对象是不能引用transient状态的对象的
            session.save(user1);//发Hibernate: insert into
            session.save(user2);//发Hibernate: insert into
            /**
             * Hibernate: insert into t_user (name, groupid) values (?, ?)
                Hibernate: insert into t_user (name, groupid) values (?, ?)
                org.hibernate.TransientObjectException: object references an unsaved transient instance
                 - save the transient instance before flushing: com.bjsxt.hibernate.Group
             */
            //也就是说：Group是一个transient,所以抛出异常
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }    
    //先存一方对象group，再存多方对象user，OK!
    public void testSave2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            Group group = new Group();
            group.setName("尚学堂");
            
            session.save(group);
            
            User user1 = new User();
            user1.setName("猪八戒2");
            user1.setGroup(group);
            
            User user2 = new User();
            user2.setName("七仙女2");
            user2.setGroup(group);
            
            //可以正确存储
            session.save(user1);
            session.save(user2);
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }    
    //先设置级联cascade属性,然后在保存的时候，只需要保存多方对象user,采用cascade属性,ok
    public void testSave3() {
        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102");
            user1.setGroup(group);
            
            User user2 = new User();
            user2.setName("容祖儿2");
            user2.setGroup(group);
            
            //不会抛出异常，因为采用了cascade属性，所以它会先保存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);
        }
    }    
    
    public void testLoad1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            User user = (User)session.load(User.class, 8);
            System.out.println("user.name=" + user.getName());
            System.out.println("user.group.name=" + user.getGroup().getName());
            
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }    
    
}