What does persistence object means in Hibernate architecture?

Question

Hibernate is a persistence framework which is used to persist data from Java environment to database.

I am so confused.. if we persist an object to the database, then why does Hibernate Architecture depicts the persistent object in the middle of Application and Hibernate in the picture below?

_{(source: viralpatel.net)}

Solution 1

I will make it more clearer. Persistent objects are instances of POJO classes that you create that represent rows in the table in the database. According to hibernate-doc an instance of POJO class representing table in database goes through 3 states of which persistent is one of them.

When a POJO instance is in session scope, it is said to be persistent i.e hibernate detects any changes made to that object and synchronizes it with database when we close or flush the session.

And about hibernate.properties and XML Mapping @Ken Chan is right. Go through hibernate-doc for more illustrations on objects in hibernate.

Solution 2

Firstly you need to understand the three states of the Hibernate object i.e Transient, Persistent, Detached.

Transient state: An object is in transient state if it just has been instantiated using the new operator and there is no reference of it in the database i.e it does not represent any row in the database.

Persistent state: An object is in the persistent state if it has some reference in the database i.e it represent some row in the database and identifier value is assigned to it. If any changes are made to the object then hibernate will detect those changes and effects will be there in the database that is why the name Persistent. These changes are made when session is closed. A persistent object is in the session scope.

Detached state: An object that has been persistent and is no longer in the session scope. The hibernate will not detect any changes made to this object. It can be connected to the session again to make it persistent again.

Solution 3

According to the figure , you configure hibernate.properties or some XML mapping to map a database table to a java object which is called persistent object .

Then in your application , you use the persistent object as a normal java object to manipulate its state . You can pass persistent object to hibernate .Hibernate will then generate and issue the necessary SQL to DB to synchronize the state of the persistent objectand its corresponding database record .Does it make sense ?

Solution 4

Persistent Objects are generally those objects that exist in memory even beyond the duration of the process that creates it. These objects are then stored in the database.

Solution 5

Persistent object is nothing but an instance of POJO class. And POJO class is nothing but a class that represents a table. And Hibernate always monitoring that persistent object. Whenever you manipulate that object or you made any changes in that object, Hibernate will do the same in that table (that one represent by the POJO class). that all handle by the hibernate. So in sort this is the one of the feature of hibernate framework.

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Comments

[Mmd]

yes, but what happens to Hibernate cash ? and is persistent object saved in DB when session is closed?@ken Chan

[Ken Chan]

in hibernate term , the persistent objects will be synchronized with DB (i.e saved/updated/deleted from DB depending on the state of the persistent objects) when the hibernate session is flushed

[Asma Rahim Ali Jafri]

this should have been the accepted answer. Great explanation, very easy.

[Dulani Maheshi]

This explanation is more clear, because of the example you provided. Thanks.