Hibernate Session

Hibernate Session Definition: 

An instance which represents a set of operations(crud) on database
A persist related interface

factory.openSession VS factory.getCurrentSession

	factory.openSession	factory.getCurrentSession
Thread	Not related	Using ThreadLocal, bind to current thread
When close	require manual close	auto close after commit or rollback
When to use	no thread related	want operation in same thread
Transaction	not required	require transaction commit
Config	not required	<property name="hibernate.current_session_context_class"> thread</property>

Session Range
<property name="hibernate.current_session_context_class"> thread</property>

hibernate.current_session_context_class: jta, thread, managed, custom.Class

jta: cross databases/hosts, remote server database
thread: local events only, for one single database

Session states: (to be introduced...)

Transient

Persistent

Detached

Functions


save
merge
persist
saveOrUpdate
lock


get
load

update


delete

session.get VS session.load

	Session.get	Session.load
Return Object	Return target object	Return a proxy of object
If result not found	Return null	Throw ObjectNotFoundException
When to use	If the result may be null	If the result is sure not be null
Cache looking sequence	Session cache(1st level) 2nd level cache SQL return	Session cache(1st level) 2nd level cache return object proxy(lazy) when use object during session: SQL & return when use object out of session: throw Exception

Session.load is using Lazy fetching mode, if hbm configures lazy to false, session.load will be the same as session.get

2nd level cache needs configuration to enable

If the same result has been checked more frequently, hibernate will move cache from 2nd level to session cache(1st level)

To cancel Lazy fetching mode, config *.hmb.xml, set <class> tag: lazy="false"

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