hibernat之3.三种状态

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状态图:

Transient（临时状态）

数据库中不存在  session中不存在

Persistent（持久化状态)

数据库中存在   session中也存在

Detached（游离状态)

数据库中存在   session中不存在

通过下面的一些例子,来看看三个状态间的转化，以及各自产生的sql语句的条数

临时状态

例一:

@Test
	public void transient01Test(){
		Student student=new Student();
		student.setStudentName("张三");
		student.setAge(20);
	}

只是单纯的new一个对象，此时数据库与session中并不存在该对象

持久化状态

例二:

@Test
<span style="white-space:pre">	</span>public void persistent01Test(){
<span style="white-space:pre">		</span>Student student=new Student();
<span style="white-space:pre">		</span>student.setStudentName("张三");
<span style="white-space:pre">		</span>student.setAge(20);
<span style="white-space:pre">		</span>Session session=null;
<span style="white-space:pre">		</span>try {
<span style="white-space:pre">			</span>session=HibernateUtil.openSession();
<span style="white-space:pre">			</span>session.beginTransaction();
<span style="white-space:pre">			</span>session.save(student);
<span style="white-space:pre">			</span>session.getTransaction().commit();
<span style="white-space:pre">		</span>} catch (HibernateException e) {
<span style="white-space:pre">			</span>e.printStackTrace();
<span style="white-space:pre">			</span>session.getTransaction().commit();
<span style="white-space:pre">		</span>}finally{
<span style="white-space:pre">			</span>HibernateUtil.closeSession(session);
<span style="white-space:pre">		</span>}
<span style="white-space:pre">	</span>}

student由临时状态转为持久化状态,可以发现数据库及session中它都存在,session存在的前提是session未关闭,

发送的sql语句:

Hibernate: insert into t_student (student_name, age, student_id) values (?, ?, ?)

例三:

@Test
	public void persistent02Test(){
		Student student=new Student();
		student.setStudentName("张三");
		student.setAge(20);
		Session session=null;
		try {
			session=HibernateUtil.openSession();
			session.beginTransaction();
			session.save(student);
			student.setStudentName("aa");
			session.getTransaction().commit();
		} catch (HibernateException e) {
			e.printStackTrace();
			session.getTransaction().commit();
		}finally{
			HibernateUtil.closeSession(session);
		}
	}

由于调用save()方法后，student对象转化为持久化对象，在session中存在,当事务提交时，hibernate会将当前sudent对象与session中的sudent,进行比较

如果两者不同，会将session中的student对象同步到数据库中,发送update语句,两者相同，不做处理.

发送sql语句:

Hibernate: insert into t_student (student_name, age, student_id) values (?, ?, ?)
Hibernate: update t_student set student_name=?, age=? where student_id=?

例四:

@Test
<span style="white-space:pre">	</span>public void persistent04Test(){
<span style="white-space:pre">		</span>Student student=new Student();
<span style="white-space:pre">		</span>student.setStudentName("张三");
<span style="white-space:pre">		</span>student.setAge(20);
<span style="white-space:pre">		</span>Session session=null;
<span style="white-space:pre">		</span>try {
<span style="white-space:pre">			</span>session=HibernateUtil.openSession();
<span style="white-space:pre">			</span>session.beginTransaction();
<span style="white-space:pre">			</span>session.save(student);
<span style="white-space:pre">			</span>student.setStudentName("aa");
<span style="white-space:pre">			</span>session.update(student);
<span style="white-space:pre">			</span>student.setAge(55);
<span style="white-space:pre">			</span>session.update(student);
<span style="white-space:pre">			</span>session.save(student);
<span style="white-space:pre">			</span>session.save(student);
<span style="white-space:pre">			</span>session.getTransaction().commit();
<span style="white-space:pre">		</span>} catch (HibernateException e) {
<span style="white-space:pre">			</span>e.printStackTrace();
<span style="white-space:pre">			</span>session.getTransaction().commit();
<span style="white-space:pre">		</span>}finally{
<span style="white-space:pre">			</span>HibernateUtil.closeSession(session);
<span style="white-space:pre">		</span>}
<span style="white-space:pre">	</span>}

若一个持久化对象若发现变化后，调用多次update()或save()也是无效的,,只有事务提交时，才会同步到数据库,发送update语句

发送sql语句:

Hibernate: insert into t_student (student_name, age, student_id) values (?, ?, ?)
Hibernate: update t_student set student_name=?, age=? where student_id=?

游离状态:

例五:

@Test
	public void detach01Test(){
		Student student=new Student();
		student.setStudentId(2);
		student.setStudentName("2b");
		student.setAge(22);
		Session session=null;
		try {
			session=HibernateUtil.openSession();
			session.beginTransaction();
			session.update(student);
			session.getTransaction().commit();
		} catch (HibernateException e) {
			e.printStackTrace();
			session.getTransaction().commit();
		}finally{
			HibernateUtil.closeSession(session);
		}
	}

此时id为2的studnet对象为游离状态（数据库中存在，session不存在）,通过调用update()方法转化为持久化状态

发送sql语句:

Hibernate: update t_student set student_name=?, age=? where student_id=?

例六:

@Test
	public void detach02Test(){
		Student student=new Student();
		student.setStudentId(2);
		Session session=null;
		try {
			session=HibernateUtil.openSession();
			session.beginTransaction();
			session.delete(student);
			session.getTransaction().commit();
		} catch (HibernateException e) {
			e.printStackTrace();
			session.getTransaction().commit();
		}finally{
			HibernateUtil.closeSession(session);
		}
	}

此时id为2的studnet对象为游离状态（数据库中存在，session不存在）,通过调用delete()方法转化为临时状态(数据中不存在,session中也不存在)

    发送sql语句:

Hibernate: delete from t_student where student_id=?

    例七:

@Test
	public void detach03Test(){
		Session session=null;
		try {
			session=HibernateUtil.openSession();
			session.beginTransaction();
			Student student=(Student)session.get(Student.class,3);
			student.setStudentName("ddddd");
			session.getTransaction().commit();
		} catch (HibernateException e) {
			e.printStackTrace();
			session.getTransaction().commit();
		}finally{
			HibernateUtil.closeSession(session);
		}
	}

调用get()方法，student由游离状态变为持久化状态,当事务提交时会比较当前对象

发送sql语句:

Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=?
Hibernate: update t_student set student_name=?, age=? where student_id=?

hibernat之3.三种状态

标签：style   blog   http   io   os   ar   java   sp   数据   

原文地址：http://blog.csdn.net/wobendiankun/article/details/40382369