Spring Data JPA DTO Projection Example

🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (178K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube

Using DTO (Data Transfer Object) projections in Spring Data JPA is a powerful way to select specific columns from a database, reducing the overhead of selecting unnecessary data. Here's a step-by-step guide on how to set up DTO projections using an Employee entity as an example.

1. Setting up the project

Ensure you have the necessary dependencies in your pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

2. Define the Entity

@Entity
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String firstName;
    private String lastName;
    private String department;
    private Double salary;

    // getters, setters, etc.
}

3. Create a DTO Projection

Suppose you want to retrieve only the firstName, lastName, and department:

public class EmployeeInfoDto {
    private final String firstName;
    private final String lastName;
    private final String department;

    public EmployeeInfoDto(String firstName, String lastName, String department) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.department = department;
    }

    // getters
}

Make sure the fields are final and initialized via a constructor. 

4. Create the Repository

Define a custom query using JPQL in the repository:

public interface EmployeeRepository extends JpaRepository<Employee, Long> {

    @Query("SELECT new com.yourpackage.EmployeeInfoDto(e.firstName, e.lastName, e.department) FROM Employee e")
    List<EmployeeInfoDto> findAllEmployeeInfo();
}

The @Query selects the desired fields and maps them to the EmployeeInfoDto. 

5. Use the Repository in a Service

Now, utilize the repository method in your service layer:

@Service
public class EmployeeService {

    @Autowired
    private EmployeeRepository employeeRepository;

    public List<EmployeeInfoDto> getAllEmployeeInfo() {
        return employeeRepository.findAllEmployeeInfo();
    }
}

6. Test the Service

Set up a test to ensure your DTO projections work correctly:

@RunWith(SpringRunner.class)
@SpringBootTest
public class EmployeeServiceTest {

    @Autowired
    private EmployeeService employeeService;

    @Test
    public void testFetchEmployeeInfo() {
        List<EmployeeInfoDto> employeeInfo = employeeService.getAllEmployeeInfo();
        for (EmployeeInfoDto info : employeeInfo) {
            assertNotNull(info.getFirstName());
            assertNotNull(info.getLastName());
            assertNotNull(info.getDepartment());
        }
    }
}

7. Why Use DTO Projections? 

Performance: By selecting only the needed columns from a database, there's less data to transfer, process, and map. 

Avoiding Fetching Sensitive Data: If an entity has sensitive attributes (like passwords or private keys), using DTOs can avoid accidentally fetching or exposing them. 

Flexibility: DTOs allow for shaping data differently based on the context. The same entity can have multiple DTOs based on different use cases.

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Build REST APIs with Spring Boot 4, Spring Security 7, and JWT

🆕 High-Demand 80–90% OFF

[NEW] Learn Apache Maven with IntelliJ IDEA and Java 25

🆕 High-Demand 80–90% OFF

ChatGPT + Generative AI + Prompt Engineering for Beginners

🚀 Trending Now 80–90% OFF

Spring 7 and Spring Boot 4 for Beginners (Includes 8 Projects)

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Building Real-Time REST APIs with Spring Boot - Blog App

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Building Microservices with Spring Boot and Spring Cloud

🌟 Top Rated 80–90% OFF
Available in Udemy for Business

Java Full-Stack Developer Course with Spring Boot and React JS

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Build 5 Spring Boot Projects with Java: Line-by-Line Coding

🌟 Top Rated 80–90% OFF

Testing Spring Boot Application with JUnit and Mockito

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Spring Boot Thymeleaf Real-Time Web Application - Blog App

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Master Spring Data JPA with Hibernate

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Spring Boot + Apache Kafka Course - The Practical Guide

🎓 Student Favorite 80–90% OFF
Available in Udemy for Business

Java Testing: Mastering JUnit 5 Framework

🆕 New 80–90% OFF

Reactive Programming in Java: Spring WebFlux and Testing

🌟 Top Rated 80–90% OFF

Spring Boot + RabbitMQ Course - The Practical Guide

🌟 Top Rated 80–90% OFF
Available in Udemy for Business

Functional Programming in Java (Includes Java Collections)

🎓 Student Favorite 80–90% OFF

ChatGPT for Java Developers: Boost Your Productivity with AI

🚀 Trending Now 80–90% OFF