Query Optimization Using QueryDSL in a Spring Boot Application

What Is QueryDSL?

QueryDSL (Query Domain Specific Language) is a Java-based framework. It is a type-safe, fluent API for building SQL-like queries in a programmatic way.

Official Documentation for the latest version of QueryDSL

Key Features and Concepts of QueryDSL

• Type Safety:
• Code Generation
• JPA Integration
• Support for Collections
• DSL for Expressing Predicates
• Support for Joins
• Extensibility

Process of Query Optimization Using QueryDSL

To optimize the query using QueryDSL in the spring boot application, We have to follow the below points.

1. Add dependency for QueryDSL in your application:

<dependency>
     <groupId>com.querydsl</groupId>
     <artifactId>querydsl-apt</artifactId>
     <version>5.0.0</version>
 </dependency>
 <dependency>
     <groupId>com.querydsl</groupId>
     <artifactId>querydsl-jpa</artifactId>
     <version>5.0.0</version>
 </dependency>

2) Create An entity Class Testing with a Primary key and two other columns:

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Entity
public class Testing {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
   
    private String firstName;
   
    private String lastName;
}

3) Create a Repository class for custom functions:

import org.springframework.beans.factory.annotation.Autowired;

import com.querydsl.jpa.impl.JPAQueryFactory;

public class TestingRepository {
    @Autowired
    private EntityManager entityManager;

    public List<Testing> findPeopleByLastName(String lastName) {
        JPAQueryFactory queryFactory = new JPAQueryFactory(entityManager);
        QTesting person = QTesting.testing;
        return queryFactory.selectFrom(person)
                .where(person.lastName.eq(lastName))
                .fetch();
    }
}

4) Create a Database table

CREATE TABLE `testing` (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `first_name` varchar(45) DEFAULT NULL,
  `last_name` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

Originally published at https://www.devstringx.com on Nov 11, 2023