Spring Boot Data JPA derived queries

last modified July 25, 2023

In this article we show how to create queries from method names.

Spring is a popular Java application framework for creating enterprise applications. Spring Boot is an evolution of Spring framework which helps create stand-alone, production-grade Spring based applications with minimal effort.

Spring Data JPA

Spring Data JPA facilitates the implementation of JPA based repositories. It enhances support for JPA based data access layers. It makes it easier to build Spring-powered applications that use data access technologies. Spring Data JPA is a part of the larger Spring Data family.

Spring Data JPA derived queries

Spring Data JPA can create queries from method names. This is a specific form of a convention over configuration. Spring Data JPA creates queries from specific keywords with combination of attributes; for instance: findByAgeLessThan, findByFirstnameEndingWith, or findByFirstnameEquals. The list of keywords is available in Spring Data JPA documentation.

Spring Boot Data JPA derived queries example

The following application is uses two derived queries.

build.gradle
...
src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           │   MyRunner.java
│   │           ├───model
│   │           │       City.java
│   │           ├───repository
│   │           │       CityRepository.java
│   │           └───service
│   │                   CityService.java
│   │                   ICityService.java
│   └───resources
│           application.properties
│           data-h2.sql
│           schema-h2.sql
└───test
    └───java

This is the project structure.

plugins {
    id 'org.springframework.boot' version '3.1.1'
    id 'io.spring.dependency-management' version '1.1.0'
    id 'java'
}

group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    runtimeOnly 'com.h2database:h2'
}

The Gradle builds file contains dependencies for H2 database and Spring Boot Data JPA.

spring.main.banner-mode=off
spring.sql.init.platform=h2
spring.jpa.hibernate.ddl-auto=none

In the application.properties file we write various configuration settings of a Spring Boot application. With the spring.main.banner-mode property we turn off the Spring banner.

The spring.sql.init.platform sets the vendor name of the database. It is used in the initialization scripts. The spring.jpa.hibernate.ddl-auto disables the automatic creation of schemas from entities.

package com.zetcode.model;

import java.util.Objects;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.Table;

@Entity
@Table(name = "cities")
public class City {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;
    private int population;

    public City() {
    }

    public City(String name, int population) {
        this.name = name;
        this.population = population;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPopulation() {
        return population;
    }

    public void setPopulation(int population) {
        this.population = population;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 79 * hash + Objects.hashCode(this.id);
        hash = 79 * hash + Objects.hashCode(this.name);
        hash = 79 * hash + this.population;
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final City other = (City) obj;
        if (this.population != other.population) {
            return false;
        }
        if (!Objects.equals(this.name, other.name)) {
            return false;
        }
        return Objects.equals(this.id, other.id);
    }

    @Override
    public String toString() {

        var builder = new StringBuilder();
        builder.append("City{id=").append(id).append(", name=")
                .append(name).append(", population=")
                .append(population).append("}");

        return builder.toString();
    }
}

This is the City entity. Each entity must have at least two annotations defined: @Entity and @Id.

@Entity
@Table(name = "cities")
public class City {

The @Entity annotation specifies that the class is an entity and is mapped to a database table. The @Table annotation specifies the name of the database table to be used for mapping.

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

The @Id annotation specifies the primary key of an entity and the @GeneratedValue provides for the specification of generation strategies for the values of primary keys.

CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255), population INT);

When the application is started, the schema-h2.sql script is executed. It creates a new database table.

INSERT INTO cities(name, population) VALUES('Bratislava', 432000);
INSERT INTO cities(name, population) VALUES('Budapest', 1759000);
INSERT INTO cities(name, population) VALUES('Prague', 1280000);
INSERT INTO cities(name, population) VALUES('Warsaw', 1748000);
INSERT INTO cities(name, population) VALUES('Los Angeles', 3971000);
INSERT INTO cities(name, population) VALUES('New York', 8550000);
INSERT INTO cities(name, population) VALUES('Brest', 139163);
INSERT INTO cities(name, population) VALUES('Edinburgh', 464000);
INSERT INTO cities(name, population) VALUES('Suzhou', 4327066);
INSERT INTO cities(name, population) VALUES('Zhengzhou', 4122087);
INSERT INTO cities(name, population) VALUES('Berlin', 3671000);
INSERT INTO cities(name, population) VALUES('Bucharest', 1836000);

Later, the data-h2.sql file is executed. It fills the table with data.

package com.zetcode.repository;

import com.zetcode.model.City;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface CityRepository extends CrudRepository<City, Long> {

    List<City> findByNameEndingWith(String ending);
    List<City> findByPopulationLessThan(int population);
}

We have two methods from which derived queries are generated.

List<City> findByNameEndingWith(String ending);

Here the query will look form city names that end with a specified string.

List<City> findByPopulationLessThan(int population);

There the query will look for cities with population less than the specified amount.

package com.zetcode.service;

import com.zetcode.model.City;

import java.util.List;

public interface ICityService {

    List<City> findByNameEndingWith(String ending);
    List<City> findByPopulationLessThan(int population);
}

ICityService provides two contract methods.

package com.zetcode.service;

import com.zetcode.model.City;
import com.zetcode.repository.CityRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class CityService implements ICityService {

    @Autowired
    private CityRepository cityRepository;

    @Override
    public List<City> findByNameEndingWith(String ending) {
        return cityRepository.findByNameEndingWith(ending);
    }

    @Override
    public List<City> findByPopulationLessThan(int population) {
        return cityRepository.findByPopulationLessThan(population);
    }
}

CityService contains the service method implementations. The derived queries are called on the cityRepository.

package com.zetcode;

import com.zetcode.service.ICityService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class MyRunner implements CommandLineRunner {

    private static final Logger logger = LoggerFactory.getLogger(MyRunner.class);

    private final ICityService cityService;

    @Autowired
    public MyRunner(ICityService cityService) {
        this.cityService = cityService;
    }

    @Override
    public void run(String... args) throws Exception {

        logger.info("Finding cities having population less than one million");
        var res1 = cityService.findByPopulationLessThan(1000000);
        logger.info("{}", res1);

        logger.info("Finding cities by name ending with 'est'");
        var res2 = cityService.findByNameEndingWith("est");
        logger.info("{}", res2);
    }
}

The MyRunner fetches all cities with population less than one million and all cities whose names end in 'est'.

package com.zetcode;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

The Application sets up the Spring Boot application. The @SpringBootApplication enables auto-configuration and component scanning.

$ ./gradlew bootRun -q
...
... Finding cities having population less than one million
... [City{id=1, name=Bratislava, population=432000}, City{id=7, name=Brest, population=139163}, 
     City{id=8, name=Edinburgh, population=464000}]
... Finding cities by name ending with 'est'
... [City{id=2, name=Budapest, population=1759000}, City{id=7, name=Brest, population=139163}, 
     City{id=12, name=Bucharest, population=1836000}]
...

We run the application.

In this article we have used Spring Data JPA derived queries to fetch data.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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