25+ Spring Data JPA Interview Questions with Answers, Explanations & Use Cases

 

📘 Spring Data JPA Interview Questions (with Answers, Explanations & Use Cases)

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1. What is JPA and how is it related to Spring Data JPA?

Answer:
JPA (Java Persistence API) is a Java specification for managing relational data. Spring Data JPA is a part of Spring Data that simplifies JPA usage by reducing boilerplate code.

Use Case:
Persisting Java objects (like User) to a relational database without writing SQL.

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2. What are the key annotations used in JPA?

Answer:
@Entity, @Table, @Id, @GeneratedValue, @Column, @ManyToOne, @OneToMany, etc.

Explanation:
These annotations map Java objects to database tables and relationships.

Use Case:
Creating a User entity with an auto-generated ID and fields mapped to table columns.

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3. What is the difference between JPA and Hibernate?

Answer:
JPA is a specification; Hibernate is an implementation of that specification.

Use Case:
Using Hibernate as the default JPA provider in Spring Boot.

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4. How do you define a primary key in JPA?

Answer:
Using @Id and optionally @GeneratedValue.

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

Use Case:
Auto-generating unique IDs for each database row.

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5. What is the purpose of JpaRepository?

Answer:
It is a Spring Data interface that provides CRUD, pagination, and custom query functionality.

Use Case:
Interacting with the User entity without writing any DAO implementation.

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6. Difference between CrudRepository and JpaRepository?

Answer:
JpaRepository extends CrudRepository and adds JPA-specific features like flushing and batch operations.

Use Case:
Use JpaRepository for advanced operations like pagination and batch inserts.

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7. How do you define custom queries in Spring Data JPA?

Answer:
Using @Query annotation.

@Query("SELECT u FROM User u WHERE u.email = ?1")
User findByEmail(String email);

Use Case:
Fetch a user by email using JPQL.

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8. How do you write native SQL queries?

Answer:
Use @Query with nativeQuery = true.

@Query(value = "SELECT * FROM users WHERE status = ?1", nativeQuery = true)
List<User> findByStatus(String status);

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9. What is the difference between JPQL and native SQL?

Answer:
JPQL uses entity names and fields; native SQL uses actual table and column names.

Use Case:
JPQL for portability; native SQL for performance optimization.

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10. What is FetchType.LAZY vs EAGER?

Answer:

• LAZY: Loads associations only when accessed.

• EAGER: Loads associations immediately.

Use Case:
Avoid performance issues by using LAZY on large data sets.

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11. How do you implement one-to-many relationship in JPA?

Answer:

@OneToMany(mappedBy = "user")
private List<Order> orders;

Use Case:
A User having multiple Order entries.

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12. How to perform pagination and sorting?

Answer:
Use Pageable and Sort in repository methods.

Page<User> findAll(Pageable pageable);

Use Case:
Display paginated results on a web page.

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13. How to use projections in Spring Data JPA?

Answer:
By using interfaces or DTOs to return partial data.

interface UserSummary {
  String getName();
  String getEmail();
}

Use Case:
Return only needed fields to reduce bandwidth.

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14. What is a DTO and why is it used in JPA?

Answer:
DTO (Data Transfer Object) is used to transfer specific data between layers.

Use Case:
Improve performance and security by not exposing entire entities.

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15. What is optimistic locking in JPA?

Answer:
Prevents data loss by using @Version to detect concurrent modifications.

Use Case:
Avoid overwriting changes in concurrent updates.

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16. How do you handle bidirectional relationships?

Answer:
Use mappedBy to define the owning side.

Use Case:
Maintain relationship between User and Order with clear ownership.

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17. How to prevent the N+1 select problem?

Answer:
Use @EntityGraph or fetch joins.

@Query("SELECT u FROM User u JOIN FETCH u.orders")
List<User> findAllWithOrders();

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18. What is cascading in JPA?

Answer:
Allows operations to propagate to related entities using cascade = CascadeType.ALL.

Use Case:
Persist or delete child entities automatically.

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19. What is save() vs saveAndFlush()?

Answer:

• save(): Persists entity but may delay DB write.

• saveAndFlush(): Immediately flushes changes.

Use Case:
Use saveAndFlush() when immediate DB sync is needed.

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20. How to enable JPA auditing?

Answer:
Use @CreatedDate, @LastModifiedDate, and @EnableJpaAuditing.

Use Case:
Track creation and update timestamps automatically.

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21. What are derived query methods?

Answer:
Methods like findByFirstNameAndLastName() are automatically implemented by Spring.

Use Case:
Avoid writing explicit queries.

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22. How to update an entity in Spring Data JPA?

Answer:
Fetch, modify, and then call save().

User user = userRepository.findById(id).get();
user.setEmail("new@example.com");
userRepository.save(user);

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23. What is @Modifying and when is it needed?

Answer:
Used with @Query for update/delete operations.

@Modifying
@Query("UPDATE User u SET u.status = ?1 WHERE u.id = ?2")
void updateStatus(String status, Long id);

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24. Can you use Spring Data JPA without Spring Boot?

Answer:
Yes, but Spring Boot simplifies configuration with auto-setup.

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25. What is the role of EntityManager in JPA?

Answer:
It provides APIs for CRUD operations and query execution manually.

Use Case:
Used in custom repository implementations.