1. What is Hibernate?
Hibernate is an open-source object-relational mapping (ORM) framework for Java. It provides a mapping between Java objects and database tables, simplifying the database access and manipulation.

2. Why should we use Hibernate?
There are several benefits of using Hibernate, including:
– Simplifies database access and reduces boilerplate code.
– Provides transparent persistence for Java objects.
– Supports caching, lazy loading, and automatic dirty checking.
– Enables easy database portability.

3. What are the core interfaces of Hibernate?
The core interfaces of Hibernate are:
– Session: Represents a single unit of work with the database.
– SessionFactory: Used to obtain a Session object.
– Configuration: Represents the configuration properties and mappings.
– Transaction: Defines the boundary of a transaction.

4. What is the difference between transient, persistent, and detached objects in Hibernate?
– Transient objects are newly created objects that are not associated with any database record.
– Persistent objects are objects that are associated with a database record and are being managed by the Hibernate session.
– Detached objects are objects that were once persistent but are no longer associated with a session. They can be reattached to a session later.

5. What is the purpose of Hibernate caching?
Hibernate caching improves application performance by reducing the number of database trips. It stores frequently accessed data in memory, reducing the latency associated with accessing it from the database.

6. What is the difference between the first-level cache and the second-level cache in Hibernate?
– The first-level cache, also known as the session cache, is associated with a Hibernate session. It is enabled by default and provides transaction-level caching.
– The second-level cache is an optional cache that is shared among multiple sessions. It provides a higher level of caching than the first-level cache and improves application performance.

7. What are the different types of associations in Hibernate?
The different types of associations supported by Hibernate are:
– One-to-One
– One-to-Many
– Many-to-One
– Many-to-Many

8. What is the difference between get() and load() methods in Hibernate?
– The get() method is used to load an object from the database immediately. It returns the object or null if not found.
– The load() method is used to load an object lazily. It returns a proxy object and only hits the database when the object’s properties are accessed.

9. What is lazy loading in Hibernate?
Lazy loading is a feature of Hibernate that loads the associated objects only when they are needed. It improves performance by minimizing the amount of data retrieved from the database.

10. What are the different object states in Hibernate?
The different object states in Hibernate are:
– Transient: An object that is not associated with any session or a persistent record.
– Persistent: An object that is associated with a session and is being managed by Hibernate.
– Detached: An object that was once persistent but is no longer associated with a session.

11. What is the HQL (Hibernate Query Language)?
HQL is a powerful object-oriented query language provided by Hibernate. It is similar to SQL but operates on objects instead of database tables. HQL queries are translated to SQL queries by Hibernate.

12. What is the difference between session.save() and session.persist() methods in Hibernate?
– The session.save() method returns the generated identifier immediately and can be called outside of a transaction.
– The session.persist() method does not return anything and must be called within a transaction.

13. What is the purpose of the @Transient annotation in Hibernate?
The @Transient annotation is used to specify that a field should not be persisted to the database. It is useful when you have a field that should not be stored permanently or when performing calculations based on other fields.

14. What is the purpose of the @GeneratedValue annotation in Hibernate?
The @GeneratedValue annotation is used to specify the strategy for generating primary key values. It can be used with the @Id annotation to automatically generate primary key values.

15. What is the purpose of the CascadeType.ALL in Hibernate?
The CascadeType.ALL allows propagating all operations (persist, remove, merge, refresh, and detach) from the parent entity to the associated entities. It saves boilerplate code by automatically applying the same operation on associated entities.

16. What is the difference between SQL and HQL in Hibernate?
– SQL (Structured Query Language) is a standard language for managing relational databases.
– HQL (Hibernate Query Language) is a higher-level object-oriented query language provided by Hibernate. It operates on objects instead of database tables.

17. What is the purpose of the @OneToMany(mappedBy = “…” ) annotation in Hibernate?
The @OneToMany(mappedBy = “…”) annotation is used to establish a one-to-many association between two entities. It specifies the mapping of the target entity’s field (the inverse side of the association).

18. What is the purpose of the @ManyToOne annotation in Hibernate?
The @ManyToOne annotation is used to establish a many-to-one association between two entities. It specifies the mapping of the source entity’s field (the owning side of the association).

19. What is the purpose of the @JoinColumn annotation in Hibernate?
The @JoinColumn annotation is used to specify the join column for an association or the foreign key for a many-to-one or one-to-one association. It defines the column in the database table that holds the foreign key value.

20. What is the purpose of the Hibernate SessionFactory?
The SessionFactory is responsible for providing sessions to the application. It is thread-safe and should be instantiated only once per application. The SessionFactory is heavyweight and initializes the mapping metadata and caches it for efficient use.

1. What is Hibernate ORM framework?
Hibernate is an object-relational mapping (ORM) framework for Java applications. It simplifies the data access layer of an application by managing the mapping between object-oriented models and relational database tables.

2. What are the advantages of using Hibernate?
– Hibernate provides a simplified programming model by eliminating the need for writing SQL queries manually.
– It offers transparent persistence, allowing the developer to work with Java objects instead of database tables.
– Hibernate provides caching mechanisms to improve performance.
– It supports automatic schema generation and synchronization.
– Hibernate supports inheritance mapping and association mapping between entities.

3. What is the difference between Session.get() and Session.load() methods in Hibernate?
The Session.get() method fetches the data immediately from the database and returns the object or null if not found. The Session.load() method returns a proxy object that represents the requested data and loads it from the database only when needed, throwing an exception if the data is not found.

4. Explain the difference between Hibernate and JDBC.
Hibernate is an ORM framework that simplifies data access and provides higher-level abstractions, while JDBC (Java Database Connectivity) is a low-level API for interacting with databases. Hibernate handles object-relational mapping, caching, and transaction management, whereas JDBC requires manual coding of SQL queries and managing database connections.

5. What is the purpose of the Hibernate SessionFactory?
The SessionFactory in Hibernate is responsible for creating sessions and managing the second-level cache. It is a thread-safe, immutable cache of compiled mappings for a specific database schema and can be used to obtain Session instances.

6. What are different caching mechanisms in Hibernate?
Hibernate provides three types of caching mechanisms:
– First-level cache (session cache): It caches objects within the session, reducing round trips to the database.
– Second-level cache: It is a session factory-level cache that stores persistent object instances and improves performance by reducing database hits.
– Query cache: It caches the result sets of queries, which helps in avoiding the execution of similar queries repeatedly.

7. What is a Hibernate transaction?
A Hibernate transaction is a sequence of database operations that are treated as a single unit of work. It allows developers to perform multiple operations (e.g., insert, update, delete) within a single transaction boundary, ensuring atomicity, consistency, isolation, and durability (ACID properties).

8. How can you handle concurrent transactions in Hibernate?
Hibernate provides a mechanism called optimistic locking to handle concurrent transactions. It involves adding a version field to the entity and using that field to track changes. If concurrent transactions attempt to modify the same record, Hibernate detects the conflict and throws an exception.

9. What is the purpose of the Hibernate HQL (Hibernate Query Language)?
Hibernate Query Language (HQL) is a powerful object-oriented query language used to write database-independent queries. It allows developers to express complex database queries using familiar object-oriented concepts, such as inheritance, polymorphism, and associations.

10. What are the different inheritance mapping strategies supported by Hibernate?
Hibernate supports three inheritance mapping strategies:
– Table per class hierarchy: It maps all subclasses to a single table.
– Table per subclass: It maps each subclass to a separate table.
– Table per concrete class: It maps each class to its table, including abstract classes.

11. How can you execute native SQL queries in Hibernate?
Hibernate provides a createSQLQuery() method to execute native SQL queries. This method allows developers to write SQL queries directly and retrieve the results as objects or collections.

12. Explain the concept of lazy loading in Hibernate.
Lazy loading is a technique used by Hibernate to load data on demand, rather than loading all associated data immediately. It improves performance by fetching only the necessary data when required. Lazy loading is controlled by Hibernate proxies, which transparently load associated objects when accessed.

13. What is the purpose of the Hibernate Criteria API?
The Hibernate Criteria API provides an object-oriented way of constructing queries without writing explicit SQL queries. It allows developers to build query criteria using a fluent API and supports various query operations, including filtering, ordering, and aggregations.

14. Explain the concept of cascading in Hibernate.
Cascading in Hibernate refers to the automatic persistence of related entities when an operation is performed on a parent entity. In other words, Hibernate can propagate changes made on a parent entity to its associated child entities.

15. What is the difference between save() and persist() methods in Hibernate?
The save() method in Hibernate returns the generated identifier immediately, while the persist() method doesn’t return any identifier value and persists the entity object in the database. The persist() method is useful when dealing with complex object graphs where cascading is required.

16. How does Hibernate handle transaction management?
Hibernate supports transaction management using the Java Transaction API (JTA) or by employing its own built-in transaction management. It provides methods for beginning, committing, and rolling back transactions, and can also participate in transaction demarcation provided by containers like Java EE application servers.

17. What is the purpose of the Hibernate Validator framework?
Hibernate Validator is a framework that provides a convenient and standardized way to validate object instances. It offers a set of validation annotations and rules that can be applied to entity classes, ensuring that the data meets specific validation criteria.

18. How can you integrate Hibernate with Spring Framework?
Hibernate can be integrated with the Spring Framework using the HibernateTemplate or the JPA EntityManager. Spring provides transaction management support through the @Transactional annotation, allowing declarative transaction demarcation without writing boilerplate code.

19. How can you improve Hibernate performance?
To improve Hibernate performance, you can consider:
– Caching: Use Hibernate’s second-level cache and query cache for frequently accessed data.
– Fetch Optimization: Use lazy loading and batch fetching to reduce the number of database round trips.
– Indexing: Add appropriate indexes to columns used in queries for faster data retrieval.
– Query Optimization: Optimize HQL queries by using appropriate joins and fetch strategies.
– Connection Pooling: Configure a connection pool to efficiently manage database connections.

20. How can you handle schema evolution in Hibernate?
Hibernate supports schema evolution through its schema generation and update features. By using configuration settings, Hibernate can automatically create or update database schemas based on the entity mappings. It supports various strategies for updating the schema, including creating or altering tables, and adding or deleting columns.