Posted on

Different Hibernate object states and their lifecycle in Hibernate | Techartifact

There are 3 hibernate object state –

1.) Persistent– Persistent object and collections are short lived single threaded objects, which store the persistence state. These objects synchronize their state with database depending on your flush strategy(i.e auto flush where as soon as setXXX() method is called or an item is removed from a set,list etc or define your own synchronization points with session.flush().transaction.commit() calls.) If you remove an item from persistence collections like a Set, it will be removed from database either immediately or when flush() or commit() is called depending on your flush strategy. They are plain old java objects(POJO) and are currently associated with session. As soon as the associated session is closed , persistence objects become detached objects and are free to use directly as data transfer objects in any application layer like business Layers, presentation layer etc.

2.) Detached – These objects and collection are instances of persistence objects that were associated with a session but currently not with associated with session. These objects can be freely used as Data Transfer Objects without having any impact on your database .Detached objects can be later on attached to another session by calling methods like session.update(), session.saveOrUpdate() etc and become persistence objects.

3.) Transient – These objects and collection are instance of persistence object that were never associated with session.These objects can be freely used as Data transfer objects without having any impact on your database. Transient objects become persistent objects when associated to session by calling session.save(), session.persist() etc.

4.) Removed State -A previously persistent object that is deleted from the database session.delete(account).Java instance may still exist, but it is ignored by Hibernate -Any changes made to the object are not saved to the database Picked up for garbage collection once it falls out
of scope
• Hibernate does not null-out the in-memory object

Posted on

Interfaces in Hibernate

There are 5 main Interfaces in Hibernate which form its lifeline. All of them are found in the org.hibernate package. An overview of the hibernate APIs can be found at www.hibernate.org

• Configuration interface

o Used to configure hibernate in any java application
o The java application is provided with a JDBC connection and resource mapping using the Configuration API
o It’s the first object a user uses while working with hibernate

• SessionFactory interface

o This interface is used to obtain session objects
o Though it is thread safe, we need one SessionFactory for each database that the application is connecting to.
o It acts as a kind of Cache storage during runtime giving the database sessions available for java objects.

• Session interface

o This is the primary Interface used by hibernate
o It is known as the hibernate’s persistence manager
o It is the interface used to obtain a transaction.
o It is different from the httpSession object and the two should not be confused.
o Session objects are not thread safe

• Transaction interface

o Though an optional API, it performs the all important task of abstracting the application from the underlying complex JDBC or JTA transaction.
o Each transaction object represents an atomic unit of work.
o Each session may have one or more transactions.

• Criteria and Query interface

o Query interface controls the “how” and “what” of executing queries on a database.
o Queries can be written in native SQL or in hibernate query language
o Criteria queries are those created using Java objects and Criteria interface is useful in helping to create them.