@Query for custom JPQL in Spring Boot - Mini Project: Build & Apply

Using @Query for Custom JPQL in Spring Boot

📖 Scenario: You are building a simple Spring Boot application to manage a list of books in a library. You want to find books by their author's name using a custom JPQL query.

🎯 Goal: Create a Spring Data JPA repository with a custom JPQL query using the @Query annotation to find books by author name.

📋 What You'll Learn

Create an entity class Book with fields id, title, and author.

Create a repository interface BookRepository that extends JpaRepository.

Add a custom method findBooksByAuthorName in BookRepository using @Query with JPQL.

Use the custom query to find all books by a given author.

💡 Why This Matters

🌍 Real World

Custom JPQL queries let you write precise database queries in Spring Boot applications, useful when default query methods are not enough.

💼 Career

Understanding @Query with JPQL is essential for backend developers working with Spring Data JPA to efficiently retrieve data from databases.

1

Create the Book entity

Create a class called Book annotated with @Entity. Add private fields Long id annotated with @Id and @GeneratedValue, String title, and String author. Include public getters and setters.

Spring Boot

// Your code here to create the Book entity class with id, title, and author fields

Need a hint?

Use @Entity on the class. Use @Id and @GeneratedValue on the id field.

2

Create the BookRepository interface

Create an interface called BookRepository that extends JpaRepository<Book, Long>. This interface will be used to access the database.

Spring Boot

import org.springframework.data.jpa.repository.JpaRepository;

// Your code here to create BookRepository interface extending JpaRepository

Need a hint?

Use public interface BookRepository extends JpaRepository<Book, Long>.

3

Add custom JPQL query method

Inside BookRepository, add a method List<Book> findBooksByAuthorName(String authorName) annotated with @Query. Use JPQL: "SELECT b FROM Book b WHERE b.author = :authorName".

Spring Boot

import org.springframework.data.jpa.repository.Query;
import java.util.List;

// Add the method with @Query annotation here
// Your code here

Need a hint?

Use @Query with JPQL string and @Param for the parameter.

4

Use the custom query method in a service

Create a class BookService with a private final BookRepository field. Add a constructor to inject BookRepository. Add a method List<Book> getBooksByAuthor(String authorName) that calls bookRepository.findBooksByAuthorName(authorName) and returns the result.

Spring Boot

import java.util.List;

// Your code here to create BookService class with constructor injection and getBooksByAuthor method

Need a hint?

Use constructor injection for BookRepository and call the custom query method inside getBooksByAuthor.