Hibernate interview questions

1. What is Hibernate?

Hibernate is a pure Java object-relational mapping (ORM) and persistence framework that allows you to map plain old Java objects to relational database tables using (XML) configuration files.Its purpose is to relieve the developer from a significant amount of relational data persistence-related programming tasks.

2. What is ORM ?

ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java application to the tables in a relational database.

3. What are the ORM levels ?

The ORM levels are:

• Pure relational
• Light objects mapping
• Medium object mapping
• Full object Mapping

4. What is a pure relational ORM?

The entire application, including the user interface, is designed around the relational model and SQL-based relational operations.

5. 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.

6. 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.

7. 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.

8. What does ORM consists of ?

An ORM solution consists of the followig four pieces:

• API for performing basic CRUD operations
• API to express queries refering to classes
• Facilities to specify metadata
• Optimization facilities : dirty checking,lazy associations fetching

9. Why do you need ORM tools like hibernate?

The main advantage of ORM like hibernate is that it shields developers from messy SQL. Apart from this, ORM provides following benefits:

• Improved productivity
• High-level object-oriented API
• Less Java code to write
• No SQL to write
• Improved performance
• Sophisticated caching
• Lazy loading
• Eager loading
• Improved maintainability
• A lot less code to write
• Improved portability

ORM framework generates database-specific SQL for you.