Hibernate 的三种状态

1.Transient 状态

　 There is no records in database.

2.Persistent状态

Data exists in database, and data has been managed by Hibernate session

3.Detached状态

Data exists in database, but data did not get managed by Hibernate session

package org.test.test;

import java.text.SimpleDateFormat;

import org.hibernate.Session;
import org.junit.Test;
import org.test.itat.model.User;
import org.test.util.HibernateUtil;

public class TestStatus {
    private static final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    @Test
    public void testTransient() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setBorn(sdf.parse("1976-2-3"));
            u.setUsername("zxl");
            u.setNickname("赵晓六");
            u.setPassword("123");
            //以上u就是Transient（瞬时状态），表示没有被session管理并且数据库中没有
            //执行save之后，被session所管理，而且，数据库中已经存在，此时就是Persistent状态
            session.save(u);

            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testPersistent01() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setBorn(sdf.parse("1976-2-3"));
            u.setUsername("zxq");
            u.setNickname("赵晓七");
            u.setPassword("123");
            //以上u就是Transient（瞬时状态），表示没有被session管理并且数据库中没有
            //执行save之后，被session所管理，而且，数据库中已经存在，此时就是Persistent状态
            session.save(u);
            //此时u是持久化状态，已经被session所管理，当在提交时，会把session中的对象和目前的对象进行比较
            //如果两个对象中的值不一致就会继续发出相应的sql语句
            u.setNickname("赵晓其");
            //此时会发出2条sql，一条用户做插入，一条用来做更新
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testPersistent02() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setBorn(sdf.parse("1976-2-3"));
            u.setUsername("zxq");
            u.setNickname("赵晓八");
            u.setPassword("123");
            session.save(u);
            u.setPassword("222");
            //下条条语句没有意义
            session.save(u);
            u.setNickname("赵晓吧");
            //下条语句没有意义
            session.update(u);
            u.setBorn(sdf.parse("1988-12-22"));
            //下条语句没有意义
            session.update(u);
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testPersistent03() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setBorn(sdf.parse("1976-2-3"));
            u.setUsername("zxq");
            u.setNickname("赵晓九");
            u.setPassword("123");
            session.save(u);
            /*
             * 以下三条语句没有任何意义，如果没有任何变化，不会发出sql语句
             */
            session.save(u);
            session.update(u);
            session.update(u);
            u.setUsername("zxj");
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testPersistent04() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            //此时u是Persistent
            User u = (User)session.load(User.class, 10);
            //由于u这个对象和session中的对象不一致，所以会发出sql完成更新
            u.setUsername("aaa");
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testPersistent05() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            //此时u是Persistent
            User u = (User)session.load(User.class, 10);
            session.getTransaction().commit();
            session.beginTransaction();
            u.setUsername("123");
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testPersistent06() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            //此时u是Persistent
            User u = (User)session.load(User.class, 11);
            u.setUsername("123");
            //清空session
            session.clear();
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testDetach01() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setId(10);
            u.setNickname("abc");
            //当执行save的时候总是会添加一条数据，此时id就会根据Hibernate所定义的规则来生成
            session.save(u);
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testDetach02() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setId(10);
            //完成update之后也会变成持久化状态
            session.update(u);
            u.setBorn(sdf.parse("1998-12-22"));
            u.setNickname("aaa");
            u.setUsername("111");
            //会发出一条sql
            session.update(u);
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testDetach03() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setId(10);
            //完成update之后也会变成持久化状态
            session.update(u);
            u.setBorn(sdf.parse("1998-12-22"));
            u.setNickname("aaa");
            u.setUsername("111");
            //会抛出异常
            u.setId(333);
            //会发出一条sql
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testDetach04() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
            u.setId(10);
            //现在u就是transient对象
            session.delete(u);
            //此时u已经是瞬时对象，不会被session和数据库所管理
            u.setNickname("abc");
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testDetach05() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            User u = new User();
//            u.setId(110);
            u.setNickname("abc");
            //如果u是离线状态就执行update操作，如果是瞬时状态就执行Save操作
            //但是注意：该方法并不常用
            session.saveOrUpdate(u);
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }

    @Test
    public void testDetach06() {
        Session session = null;
        try {
            session = HibernateUtil.openSession();
            session.beginTransaction();
            //u1已经是持久化状态
            User u1 = (User)session.load(User.class, 11);
            System.out.println(u1.getNickname());
            //u2是离线状态
            User u2 = new User();
            u2.setId(11);
            u2.setPassword("12223");
            //此时u2将会变成持久化状态，在session的缓存中就存在了两份同样的对象,在session中不能存在两份拷贝，否则会抛出异常
//            session.saveOrUpdate(u2);
            //merge方法会判断session中是否已经存在同一个对象，如果存在就将两个对象合并
            session.merge(u2);
            //最佳实践：merge一般不用
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            if(session!=null) session.getTransaction().rollback();
        } finally {
            HibernateUtil.close(session);
        }

    }
}