Efficient Data Queries with Spring Data JPA Projections

July 26, 2023
3 minutes to read
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In the world of JVM Backend Development, efficient data processing is a crucial concern. One of the main strengths of Spring Data JPA lies in its ability to simplify and optimize interaction with the persistence layer. A particularly powerful feature provided by Spring Data JPA is the use of projections. They offer an excellent way to make data queries more efficient and improve system performance.

What are Spring Data JPA Projections?

Spring Data JPA projections allow you to create custom Partial Views of your entity classes. This means that instead of retrieving a complete entity, you can only retrieve selected fields, significantly reducing the size of the returned data and thereby improving the overall performance.

Suppose you have a Product entity class that has various attributes such as id, name, description, price, and manufacturer. But in certain queries, you might only need the name and price. This is where projections come into play.

Creating Your Entity Classes

Before we start with the projections, we need a Spring Boot application and a Product entity class first.

public class Product {
    private UUID id = UUID.randomUUID();
    private String name;
    private String description;
    private Double price;
    private String manufacturer;
    // ...

Defining Projection Interfaces

Spring Data JPA supports different types of projections, and in this article, we will focus on interface-based projections.

To create an interface-based projection, you simply define an interface with the desired getter methods. Here is an example:

public interface ProductSummary {
    String getName();
    Double getPrice();

Now, Spring Data JPA will generate an implementation that extracts exactly the name and price attributes from your Product entity.

Defining Projection Methods in the Repository

To use our defined projection, we add a method to our ProductRepository that uses the ProductSummary projection as the return type.

public interface ProductRepository extends JpaRepository<Product, Long> {
    ProductSummary findProductSummaryById(UUID id);

This method will return a ProductSummary object, which contains only the name and price attributes of a Product object.

The Performance Advantage of Projections

But why are projections so important for performance? Well, it’s because of how SQL queries are processed.

Suppose we want to retrieve all products without using a projection. The generated SQL query would look something like this:

SELECT * FROM product

This query fetches all fields of every row from the product table. This can result in significant network and memory overhead, particularly with large tables.

However, if we use a projection to only retrieve name and price, the generated SQL query looks different:

SELECT name, price FROM product

This query only fetches the name and price fields from each product. This means that less data needs to be transmitted over the network and held in memory, which can lead to a significant improvement in performance.


Spring Data JPA projections are a powerful tool for increasing data query efficiency. By selectively choosing the required data, you can improve the performance of your system while also increasing the readability and maintainability of your code. With this new knowledge, you are ready to take your data queries to the next level!

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