Hibernate Learning-11: Persistent object state and state transitions, persistent object Automatic Update database

Persistence class: An entity class that establishes a mapping with a database table.

Hibernate in order to facilitate the management of persistent classes, the persistence class is divided into three states.

Transient state Transient:(temporary State) features: Persistent objects do not have a unique identifier OID. Management without a session

Persistent state persistent: Features: persistent objects have a unique identifier OID. Management that has been included in the session

Off-state detached:(off-line state) features: Persistent objects have a unique identifier OID, not included in the session management

1. Distinguish the state of three persistent objects

Take a look at the following example:

@Test
	//distinguish three states of persisted objects: public
	void Demo1 () {
		//1. Creating session Session Session
		= Hibernateutils.opensession ();
		2. Turn on transaction
		Transaction tx = Session.begintransaction ();
		
		Save a book to the database: Books
		= new ();	Transient state: There is no uniquely identified OID and is not associated with the session.
		Book.setname ("hiernate development");
		Book.setauthor ("Sun xx");
		Book.setprice (65d);
		
		Session.save (book); Persistent state: Has a uniquely identified OID, which is associated with the session.
		
		3. Transaction submission
		Tx.commit ();
		4. Release of resources
		Session.close ();
		
		Book.setname ("Struts2 development"); Off-state: There is a unique identifier, not associated with the session.
	}

2. Three state object conversions:

instantaneous state:

Get:

Book book = new book ();

Instantaneous state-to-last state:

Save (book);

Save ()/saveorupdate ();

Instantaneous state-to-off state:

Book.setid (1);

Persistent State:

Get:

Book book = (book) session.get (book.class,1);

Get ()/load ()/find ()/iterate ();

Persistent state-to-instantaneous state:

Delete (book);

Special status: Delete state. (Deleted objects are not recommended to use.)

Persistent---off-pipe state:

Session.close ();

Close ()/clear ()/evict ();

off-pipe state:

Get:

Book book = new book ();
Book.setid (1);

Off-state---persistent state:

Session.update ();

Update ()/saveorupdate ()/lock ()

Off-state-instantaneous state:

Book.setid (NULL);

Persistent objects have the ability to automatically update the database, for example:

@Test
	//test Persistent state objects automatically update the database public
	void Demo2 () {
		//1. Create session Session Session
		= Hibernateutils.opensession ();
		2. Turn on transaction
		Transaction tx = Session.begintransaction ();
		
		Gets the object of a persistent state.
		Book book = (book) session.get (Book.class, 1);
		Book.setname ("Struts2 development");
		
		Session.update (book);
		
		3. Submission of transaction
		Tx.commit ();
		4. Close Resource
		session.close ();
	}

The ability to automatically update a database relies on Hibernate's first-level cache. We'll show you a bit more about the first-level cache and the level two cache.