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Friday, May 5, 2023

Top 20 Spring Data JPA Interview Questions Answers for Java Developers

Hello guys, if you are preparing for Spring and Java developer job interview and looking for common Spring Data JPA interview questions then you have come to the right place. Earlier, I have shared spring boot questions, spring cloud questions, spring security questions, and spring MVC questions and in this article, I am going to share 20 common Spring Data JPA questions with answers. These are simple questions focused on key Spring Data JPA concepts like finder methods, query methods, pros and cons of Spring Data JPA, how to implement Spring Data JPA repository interface etc. If you have done work or used Spring Data JPA in your project then most likely you will be familiar with those concepts but if not then don't worry, you can also checkout these Spring Data JPA courses to learn them in detail. 

Spring Data JPA is an important topic and in the past few years, not only its usage has increased but also its importance on Interviews. I have seen at least one question about Spring Data JPA on Java interviews. Most people ask about repository interface, finder methods and Query annotation but there are a lot more to learn on Spring Data JPA.

If you are looking for the way forward as far as preparing for a Spring Cloud JPA interview is concerned? Worry no more because you have just come to the right place and you will leave this article smiling because what you need is what you are just going to get in a moment.

Getting to know the questions that are commonly asked in an interview is the best way to prepare yourself. In this article, I have highlighted for you 20 questions that you will not miss in a Spring Cloud JPA interview.

While I have tried to cover key concepts, the list is by no means this list of Spring Data questions are complete and I plan to add more Spring Data questions on this list to make it even more useful. You can also contribute with any Spring Data JPA question you have been asked during interview to highlight any important topic which is missed in this list.

20 Spring Data JPA Interview Questions with Answers for 3 to 5 Years Experienced Java Programmers

Without wasting anymore of your time, here is a list of common Spring data JPA Interview questions for Java developers. You can use this list of Spring Data JPA questions to quickly revise the key concepts like what is repository, what are common spring data annotations, what are query methods and how does they help with persistence layer and all. 

1. What is JPA?
Answer: JPA stands for Java Persistence API. This is a Java specification used to persist data between the relational database and Java objects. It is the bridge between object-oriented domain models and relational databases.

2. What are the advantages of JPA?
  • JPA is user-friendly
  • It helps to reduce the burden of interacting with databases
  • Through annotation, it helps in reducing the cost of creating a definition file.
  • Useful in merging applications
  • Makes user programming easy

3. What are the different types of entity mapping?
  • One-to-one mapping
  • One-to-many mapping
  • Many-to-one mapping
  • Many-to-many mapping

4. Why is an interface not a class?
Answer: The reason why interface is not a class it is because it does not contain concrete methods. The only thing it can contain is abstract methods. 

5. What is an entity?
Answer: An entity refers to a group of states associated together in a single unit.

6. Discuss the important predefined repository interfaces and classes in Spring Data JPA
  • Repository – this is a top-level interface defined in Spring Data Hierarchy
  • CrudRepository – CrudRepository interface extends Repository interface and it also provides methods that help to perform CRUD operation.
  • PagingAndSortingRepository – this interface extends CrudRepository interface and provides additional methods to retrieve entities using the pagination and sorting.
  • QueryByExampleExecutor – this interface is used to execute Query by example.
  • JpaRepository – JpaRepository interface extends PagingAndSortingRepository and QueryByExampleExecutor interface. It also helps in providing some additional batch methods.
  • SimpleJpaRepository – SimpleJpaRepository is basically the implementation class of the CrudRepository interface.
  • QueryDslRepository – this is a class.

7. What is Object Relational Mapping (ORM)?
Answer: Object Relational Mapping (ORM) is defined as a mechanism responsible for maintaining the relationship between object oriented data structures and relational tables in a database. Common ORM frameworks are JPOX, ORMLite, Toplink, Hibernate and iBatis.

8. What are the differences between JpaRepository and CrudRepository?



It extends QueryByExampleExecutor and PagingAndSortingRepository interface

it extends Repository interface

The saveAll method of JpaRepository returns list

The saveAll method of CrudRepository returns Iterable

Provides additional methods like deleteInBatch(), flush() and others

Provides methods to perform CRUD operations

9. What is the difference between getOne() and findById()?
Answer: getOne() is available in JpaRepository while findById() is available in CrudRepository.

10. What methods of CrudRepository apply in performing CRUD operations?
  • existsById – used to check if an entity of a given id already exists in the database.
  • findAll() – find all entity of particular type.
  • save(S entity) – it is used to save a single entity at a time.
  • findById – used to get entity by id.
  • findAllById – returns al entities of given ids.
  • deleteById – used to delete the entity basing on id.
  • count() – it returns the given number of entities.
  • deleteAll() – delete all entities.

11. What does the @Entity annotation do?
Answer: the @Entity annotation indicates a class represents a relational table in the database. The JPA specification includes any class marked with @Entity in the persistence setup.

20 Spring Data JPA Interview Questions with Answers

12. What does the @EnableJpaRepositories annotation do?
Answer: this annotation enables the automatic generation of JPA repositories. Any class which implements CrudRepository interface will generate a repository when this annotation is present.

13. What does the @Query annotation do? (answer)
Answer: The @Query annotation allows you to define a Spring Data Repository method with custom SQL. With the use of @Query, you can map Spring Data Repository methods to actual SQL statements.

14. What does the @Id annotation do?
Answer: The @Id annotation marks a field as the primary key for that particular table. It is a unique identifier for each entry in the table. @Id annotation is typically used with @GeneratedValue to automatically generate a unique id for each entry in the table.

15. What is the difference between Hibernate and Spring Data JPA?
Answer: Hibernate is a JPA implementation while Spring Data JPA is a JPA Data Access Abstraction.

16. How is a custom repository created in Spring data JPA?
Answer: A custom repository is created when it is extended to any of the following interfaces: CrudRepository, JpaRepository, Repository, QueryByExampleRepository and PagingAndSortingRepository.

17. What does the @GeneratedValue annotation do?
Answer: The @GeneratedValue annotation is used to specify the primary key generation strategy to use. If by any chance the strategy is not specified by default AUTO will be used.

18. What is the difference between FetchType.Eager and FetchType.Lazy?
Answer: FetchType attribute indicates how whether records will be eagerly or lazily loaded from the database. When the records are eagerly loaded, JPA returns these objects regardless of whether they are accessed by the client or not. When records are lazily loaded the actual objects are only retrieved when directly accessed. This helps in saving memory and processing when appropriate.

19. What does @Column annotation do?
Answer: The @Column annotation is utilized to designate the details of the column to which a field or property will be mapped.

20. What does the @EntityScan annotation do?
Answer: If the entity classes are not placed in the main application package or its sub package, then it is required to declare the package in the main configuration class with @EntityScan annotation.

That's all about the 20 Spring Data JPA Interview Questions with Answers. As I said, you can use this list of questions to quickly revise the key Spring Data JPA concepts before you go for any interview. I hope you are now satisfied and smiling because you have come across the right material that has what you have been looking for. 

The questions that you have seen in this articles are the similar questions that you will be meeting in your interview.  If you have keenly gone through them and mastered everything as required, you have no reason whatsoever to panic or feel you have not prepared well. Just keep calm and get into that interview with full confidence and you will surely make it.

    Thanks for reading this article so far. If you find this Spring Data JPA interview questions and answers useful, please share them with your friends and colleagues. If you have any questions or feedback, then please drop a note.

    P. S. - If you are new to Spring Framework and looking for free online courses to learn Core Spring, Spring MVC, and Spring Boot then you can also checkout this list of best free Spring Framework courses for Java developers.

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