Hibernate Interview Questions Preparation Course

Key Characteristics of Hibernate:

• Object-Relational Mapping (ORM): Hibernate maps Java objects to database tables and vice versa, simplifying data persistence.
• SQL-like Query Language: HQL provides a more intuitive way to retrieve and manipulate data from the database without writing raw SQL.
• Caching: It can cache frequently accessed data to improve performance and reduce load on the database server.
• Transactions: Hibernate manages transactions, ensuring data integrity and consistency.
• Query Results Binding: Maps query results to Java objects or collections of objects easily.
• Rich Interface for Database Operations: It provides various APIs for fetching, updating, deleting, and retrieving data in a generic manner.

Core Interfaces of Hibernate Framework:

• Session: The primary interface used to interact with the persistent object.
• Transaction: Used to manage transactions in a Session.
• Query or Criteria: Used to query and retrieve data from the database.
• SessionFactory: Builds a Session, which is used to interact with the database.
• Configuration: Configures the Hibernate session factory.

Mapping Columns to Java Class Properties:

• Using XML mapping files (.hbm.xml) or annotations, you define the mapping between the Java class properties and the database table columns.
• The mapping can specify column names, relationships, table-specific details, etc.

Mandatory Mapping File Extension:

• Traditionally, Hibernate mapping files have the .hbm.xml extension, but this is not strictly mandatory with modern annotation support.

Creating a SessionFactory in Hibernate:

• Read the configuration file (XML or properties).
• Create a Configuration instance.
• Add the resource mappings (if using XML).
• Build the SessionFactory from the configuration.

Use of POJO in Hibernate:

• POJOs (Plain Old Java Objects) are used because they are simple, portable, and can be easily mapped to database tables without needing to extend specific classes or implement specific interfaces.

Hibernate Query Language (HQL):

• HQL is a high-level query language similar to SQL but designed for Java objects. It allows users to write queries using the domain model rather than the database schema.

Calling a Stored Procedure:

• You can call stored procedures using the Session interface by creating a custom SQL query or using the Callback interface for more complex operations.

Criteria API in Hibernate:

• The Criteria API provides a powerful way to programmatically specify criteria for querying persistent entities without writing HQL strings.

Use of HibernateTemplate:

• HibernateTemplate is an alternative to the Session interface, offering a consistent set of operations for simpler applications or as a learning tool. It's deprecated in favor of the Session API due to its limitations and lack of certain features.

Viewing SQL Code Generated by Hibernate:

• Set the hibernate.show_sql property to true in the configuration file or use logging interceptors like SLF4J with appropriate log level for debugging.

Different Types of Collections Supported by Hibernate:

• List, Set, Map, Bag, and Multimap. Hibernate 5 introduced Collection as a unified collection abstraction that is equivalent to List and Set combined.

Difference between session.save() and session.saveOrUpdate():

• session.save(object) persists a new transient object.
• session.saveOrUpdate(object) saves the state of a persistent or transient object, which means it will save a new object if it's not already associated with the session, or it will update an existing one if it is.

Advantages of Hibernate over JDBC:

• Abstraction from SQL and database access.
• Increased productivity due to ORM capabilities.
• Improved maintainability due to less code and clearer separation between logic layers.
• Enhanced performance due to caching and batch operations.
• Database agnosticism, as it can work with different databases with minimal changes.

Transactions:

• Hibernate provides a Transaction API for managing transactions in a Session.

Rich Object-Oriented APIs:

• Hibernate offers a rich set of object-oriented APIs to interact with the database, such as Criteria and EntityCriteria for querying and Envers for auditing.

Caching:

• Hibernate has both first-level and second-level caches to improve performance by reducing the number of queries executed against the database.

Interactive SQL Logging:

• Hibernate allows you to log the actual SQL statements being generated, which is useful for debugging or understanding what is happening under the hood.

Fetch Profile and Result Transformer:

• Fetch profiles allow you to specify fetching strategies (eager, lazy) for associations.
• Result transformers enable you to post-process query results according to certain rules.

JPA vs Hibernate:

• Hibernate is an implementation of the Java Persistence API (JPA). JPA provides a standard API for data persistence, which can be used independently of Hibernate. However, Hibernate was the reference implementation that inspired the development of JPA.

Envers:

• Envers is an auditing extension for Hibernate that supports different types of auditing such as historical and versioned data management.

Lazy Initialization:

• Hibernate supports lazy initialization, which defers the loading of data until it is explicitly requested, to improve application performance by reducing the initial load on the database.

Batch Operations:

• Hibernate provides support for batch operations to execute multiple insert, update, or delete statements in a single transaction to optimize database performance.

Internationalization and Localization:

• Hibernate supports storing locale-specific data and generating SQL queries suitable for different locales.

Integration with Spring Framework:

• Hibernate integrates seamlessly with the Spring Framework, leveraging aspects like dependency injection, transaction management, and aspect-oriented programming to enhance modularity and manageability of applications.

Hibernate Search:

• Hibernate Search is an extension for full-text search capabilities on top of Hibernate's data access engine.

Hibernate Validator:

• Hibernate Validator provides powerful constraint validation for JavaBeans, leveraging the Java EE Bean Validation API.