Hibernate persisted Object state

Persisted object PO class state

1. Status classification

transient transient state: Hibernate's session cache is not stored and no data is in the database. For example, New PO class, no OID value

Persistent Persistent state: Hibernate is stored in the session cache and will eventually be in the database. For example, Save (PO) completes a commit operation with an OID value

Detached off-state: Hibernate does not have a session cache, and data is in the database. Out of session management, with OID values

2.OID

Oid:hibernate for Marking PO classes

Java Distinguished object: Address

Data-differentiated data: primary key is different

For example:

New Student (). SETSID (1)

New Student (). SETSID (1)

Consider two identical PO classes

3. Transitions between states

Instantaneous state:

Convert Persistent State: Save () | Saveorupdate () If there is an OID will execute Saveorupdate (), no OID will execute save ()

Off-state: Manually Set OID

Student stu = new Student (); Instantaneous state

STU.SETSID (1)//off-pipe, throws an exception if the OID corresponding data in the database does not exist

Persistent State:

Transient state: Execute delete () remember. The internet says: Delete State, the official did not give

Off-pipe: Evict, close, clear

Evict (): Removes the specified PO class from the session

Clear (): Clears the session cache, clears all

Close (): Session Close does not exist session cache

Off-pipe State:

Transient state: Execute delete () manually remove OID

Persistent state: Execute update (), Saveorupdate ()

4. First level cache

First -level cache: Refers to hibernate session level cache, in session cache data

Get () queries the PO class by ID, caches the results of the query to the first level cache (session)

The code is as follows

Package cn.hibernate.test;

Import org.hibernate.Session;
Import Org.hibernate.SessionFactory;
Import org.hibernate.cfg.Configuration;
Import Org.junit.Test;

Import cn.hibernate.bean.Student;

Public class Cachetest {

private Sessionfactory factory = new Configuration ()
. Configure (). addclass (Student.class)
. Buildsessionfactory ();

@Test
Public void Demo01 () {
Session session = Factory.opensession ();
//Query student object with ID 1
/*hibernate:
load Cn.hibernate.bean.Student Select
Student0_.sid as sid0_0_,
Student0_.sname as sname0_0_
from
Student student0_
where
student0_.sid=?
Student [Sid=1, sname=333]
*/
Student student= (Student) Session.get (Student.class, 1);
System.out.println (student);
}

@Test
Public void Demo02 () {
Session session = Factory.opensession ();
//Query two times ID 1 student object, supposedly produce two SQL statements, in fact, there is only one. But there are two output of the same object
/*hibernate:
load Cn.hibernate.bean.Student Select
Student0_.sid as sid0_0_,
Student0_.sname as sname0_0_
from
Student student0_
where
student0_.sid=?
Student [Sid=1, sname=333]
Student [Sid=1, sname=333]
*/
Student student= (Student) Session.get (Student.class, 1);
System.out.println (student);
//Call the evict () method to clear the student object in session to further see the resulting SQL statement
//Session.evict (student);
System.out.println ("********************************************");
/*hibernate:
load Cn.hibernate.bean.Student Select
Student0_.sid as sid0_0_,
Student0_.sname as sname0_0_
from
Student student0_
where
student0_.sid=?
Student [Sid=1, sname=333]
Hibernate:
load Cn.hibernate.bean.Student Select
Student0_.sid as sid0_0_,
Student0_.sname as sname0_0_
from
Student student0_
where
student0_.sid=?
Student [Sid=1, sname=333]
*/
Student student1= (Student) Session.get (Student.class, 1);
System.out.println (student1);
}

}

Hibernate persisted Object state