Hibernate re-engagement with core development interfaces

1. You can overload the method to specify the configuration file

New Annotationconfiguration (). Configure ("hibernate.xml"). Buildsessionfactory ();

So the reading is hibernate.xml but generally not recommended to modify

Getcurrentsession refers to a context that does not create a new session if it is not committed

Opensession always opens a new session for authenticating transaction boundaries such as join log operations, etc.

Transaction: Either done at the same time or rolled back

    <property name="current_session_context_class">thread</property>

Find from current thread

There are several other parameters:

such as JTA, Managed,custorm.class, etc.

Thread uses database links as transaction management

But you can't manage distributed transactions

JTA (Java trasaction API) is often used in distributed

Requires a manager to manage operations on a two-database deployment

If you don't set the context, he can't find it.

Opensession try not to use the same session with Getcurrentsession.

A cache is an area of memory where we want to improve the efficiency of reading objects

Three states of an object

Transient Persistent Detached

Transient memory has an object but there is no database in the ID cache and no

There is a database in the persistent cache and there is an ID session with key and value

There is no database in detached cache

Three states are distinguished by:

There is no ID

ID in the database has no

Not in memory (session cache)

Session Management Task Unit management of a database operation of the increment and revise check

Save slightly

Delete

As long as the ID includes a detach state, you can delete

For example:

@Test Public voidTestdelete () {Teacher T=NewTeacher (); T.setname ("T1"); T.settitle ("Middle"); T.setbirthdate (NewDate ()); Session Session=sessionfactory.getcurrentsession ();        Session.begintransaction ();        Session.save (t); System. out. println (T.getid ());                Session.gettransaction (). commit (); Session Session2=sessionfactory.getcurrentsession ();        Session2.begintransaction ();        Session2.delete (t);    Session2.gettransaction (). commit (); } @Test Public voidTestDelete2 () {Teacher T=NewTeacher (); T.setid (2); Session Session2=sessionfactory.getcurrentsession ();        Session2.begintransaction ();        Session2.delete (t);    Session2.gettransaction (). commit (); }    

Load Read

@Test      Public void testLoad () {            = sessionfactory.getcurrentsession ();        Session.begintransaction ();         = (Teacher) session.load (Teacher.  Class1);                Session.gettransaction (). commit ();        System.  out . println (T.getclass ());         // System.out.println (T.getname ());     }    

1 can be automatically packaged

Get can also take data

    @Test    publicvoid  testget () {            =  Sessionfactory.getcurrentsession ();        Session.begintransaction ();         = (Teacher) session. Get (Teacher. class 1 );                Session.gettransaction (). commit ();        System.  out . println (T.getclass ());         // System.out.println (T.getname ());    }

The difference between the two:

It is important to note that the get and load methods have significant differences. The load type is a proxy that generates an SQL statement when you really want to use the properties of the object and get is immediately sent

Update

Update an object of detach

  @Test  public  void   TestUpdate1 () {Session session  = sessionfactory.getcurrentsession ();        Session.begintransaction (); Teacher t  = (Teacher) session. get  (Teacher.                class , 1  );                Session.gettransaction (). commit (); T.setname (  " zhanglaoshi   " );        Session session2  = sessionfactory.getcurrentsession ();        Session2.begintransaction ();                Session2.update (t);    Session2.gettransaction (). commit (); }

Update transient will error but update with ID transient not error (database has corresponding record)

    @Test    publicvoid  testUpdate4 () {                        =  Sessionfactory.getcurrentsession ();        Session.begintransaction ();         = (Teacher) session. Get (Teacher. class 1 );        T.setname ("zhangsan2");        Session.gettransaction (). commit ();    }

The above update will update all fields to improve efficiency so grope

How to change only the fields you want

If it is a P object, the update will occur whenever you set the field

@Test Public voidTestUpdate5 () {Session session=sessionfactory.getcurrentsession ();        Session.begintransaction (); Student s= (Student) session.Get(Student.class,1); S.setname ("Zhangsan5");  Session.gettransaction (). commit (); //discover objects with different automatic update in databaseS.setname ("Z4"); Session Session2=sessionfactory.getcurrentsession ();        Session2.begintransaction ();        Session2.update (s);    Session2.gettransaction (). commit (); }

But this update is still the whole

To implement updating only the fields you want to update

There are three ways to do this:

1. Add Column = False property

or XML joins column = False property

2. Add in XML

    <class name="com.bjsxt.hibernate.Student"dynamic-update="  true">

This will only update the fields you want to change when the database is submitted.

However, it is important to note that this object cannot be updated so that it is updated or all fields once it is in the detach state and commits a commit.

@Test Public voidTestUpdate6 () {Session session=sessionfactory.getcurrentsession ();        Session.begintransaction (); Student s= (Student) session.Get(Student.class,1); S.setname ("zhangsan6");                Session.gettransaction (). commit (); S.setname ("Z4"); Session Session2=sessionfactory.getcurrentsession ();        Session2.begintransaction ();    Session2.merge (s);//merge can merge objects so that there is no need to send extra modifications to other fields session2.gettransaction (). commit (); }

The third is that the HQL statement will also be detailed later

@Test      Public void TestUpdate7 () {                        = sessionfactory.getcurrentsession ();        Session.begintransaction ();         = Session.createquery ("update Student s set s.name= ' Z5 ' where s.id = 1");        Q.executeupdate ();        Session.gettransaction (). commit ();            }

Save Orupdate

@Test Public voidtestsaveorupdate () {Teacher T=NewTeacher (); T.setname ("T1"); T.settitle ("Middle"); T.setbirthdate (NewDate ()); Session Session=sessionfactory.getcurrentsession ();        Session.begintransaction ();                Session.saveorupdate (t);                Session.gettransaction (). commit (); T.setname ("T2"); Session Session2=sessionfactory.getcurrentsession ();        Session2.begintransaction ();        Session2.saveorupdate (t);            Session2.gettransaction (). commit (); }

If you don't have anything, save it and update it.

Clear

Either load or get will first look for the cache (one-level cache), if not, will go to the database lookup, call the Clear method to force clear session cache

@Test Public voidTestclear () {Session session=sessionfactory.getcurrentsession ();        Session.begintransaction (); Teacher T= (Teacher) session.load (Teacher.class,1); System. out. println (T.getname ()); Session.clear ();//If you do not add this sentence will only issue a select SQL statement, added after clearing the session cache below the need to re-send the Teacher T2= (Teacher) session.load (Teacher.class,1); System. out. println (T2.getname ());                    Session.gettransaction (). commit (); }

Flush method

Forcing cached content to synchronize with database content

Specifically at what time the flush is set by Flushmode

@Test Public voidTestflush () {Session session=sessionfactory.getcurrentsession ();        Session.begintransaction (); Teacher T= (Teacher) session.load (Teacher.class,1); T.setname ("TTTT");      Session.flush (); Forces synchronization with the database, issuing an update t.setname ("TTTTT");  Session.gettransaction (). commit (); Find inconsistencies and then issue update}

Testschemaexport

You can not let him build the table automatically in the configuration file.

Then write your own class-building table

First parameter this refers to whether the DDL statement is displayed the second parameter is whether to execute the DDL statement

@Test      Public void Testschemaexport () {        new schemaexport (new annotationconfiguration (). Configure ()). Create (falsetrue);    }

Hibernate re-engagement with core development interfaces