Hibernate Interview Questions

1.What is Hibernate?
Hibernate is a powerful, high performance object/relational persistence and query service. This lets the users to develop persistent classes following object-oriented principles such as association, inheritance, polymorphism, composition, and collections.

2.What is ORM?
ORM stands for Object/Relational mapping. It is the programmed and translucent perseverance of objects in a Java application in to the tables of a relational database using the metadata that describes the mapping between the objects and the database. It works by transforming the data from one representation to another.

3.What does an ORM solution comprises of?
It should have an API for performing basic CRUD (Create, Read, Update, Delete) operations on objects of persistent classes
Should have a language or an API for specifying queries that refer to the classes and the properties of classes
An ability for specifying mapping metadata
It should have a technique for ORM implementation to interact with transactional objects to perform dirty checking, lazy association fetching, and other optimization functions

4.What are the different levels of ORM quality?

There are four levels defined for ORM quality.

Pure relational

Light object mapping

Medium object mapping

Full object mapping

5.What is a pure relational ORM?
The entire application, including the user interface, is designed around the relational model and SQL-based relational operations.

6.What is a meant by light object mapping?
The entities are represented as classes that are mapped manually to the relational tables. The code is hidden from the business logic using specific design patterns. This approach is successful for applications with a less number of entities, or applications with common, metadata-driven data models. This approach is most known to all.

7.What is a meant by medium object mapping?
The application is designed around an object model. The SQL code is generated at build time. And the associations between objects are supported by the persistence mechanism, and queries are specified using an object-oriented expression language. This is best suited for medium-sized applications with some complex transactions. Used when the mapping exceeds 25 different database products at a time.

8.What is meant by full object mapping?
Full object mapping supports sophisticated object modeling: composition, inheritance, polymorphism and persistence. The persistence layer implements transparent persistence; persistent classes do not inherit any special base class or have to implement a special interface. Efficient fetching strategies and caching strategies are implemented transparently to the application.

9.What are the benefits of ORM and Hibernate?
There are many benefits from these. Out of which the following are the most important one.
Productivity – Hibernate reduces the burden of developer by providing much of the functionality and let the developer to concentrate on business logic.

Maintainability – As hibernate provides most of the functionality, the LOC for the application will be reduced and it is easy to maintain. By automated object/relational persistence it even reduces the LOC.

Performance – Hand-coded persistence provided greater performance than automated one. But this is not true all the times. But in hibernate, it provides more optimization that works all the time there by increasing the performance. If it is automated persistence then it still increases the performance.

Vendor independence – Irrespective of the different types of databases that are there, hibernate provides a much easier way to develop a cross platform application.

10.How does hibernate code looks like?

Session session = getSessionFactory().openSession();
Transaction tx = session.beginTransaction();
MyPersistanceClass mpc = new MyPersistanceClass ("Sample App");
session.save(mpc);
tx.commit();
session.close();

The Session and Transaction are the interfaces provided by hibernate. There are many other interfaces besides this.