Spring data jpa: Extract specific fields from table

Below snippet extract firstName and lastName from employee table.

@Query("SELECT e.firstName, e.lastName " + "FROM Employee e " + "WHERE e.id in :ids ")

List<Object[]> findFirstAndLastNames(@Param(value = "ids") List<Integer> ids);

Find the below working application.

Step 1: Create new maven project ‘springDataExtractFields’.

Step 2: Update pom.xml with maven dependencies.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>springdataExtractFields</groupId>
 <artifactId>springdataExtractFields</artifactId>
 <version>1</version>

 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.1.6.RELEASE</version>
 </parent>

 <properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 </properties>


 <dependencies>

  <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-jpa -->
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-data-jpa</artifactId>
  </dependency>


  <!-- https://mvnrepository.com/artifact/com.h2database/h2 -->
  <dependency>
   <groupId>com.h2database</groupId>
   <artifactId>h2</artifactId>
  </dependency>

 </dependencies>
</project>

Step 3: Create a package ‘com.sample.entity’ and define class Employee.

Employee.java    

package com.sample.app.entity;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "employees")
public class Employee {

 @Id
 private int id;
 private String firstName;
 private String lastName;

 public Employee() {
 }

 public Employee(int id, String firstName, String lastName) {
  super();
  this.id = id;
  this.firstName = firstName;
  this.lastName = lastName;
 }

 public int getId() {
  return id;
 }

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

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 @Override
 public String toString() {
  return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + "]";
 }

}

Step 4: Create a package ‘com.sample.app.repository’ and define EmployeeRepository interface like below.

EmployeeRepository.java    

package com.sample.app.repository;

import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;

import com.sample.app.entity.Employee;

public interface EmployeeRepository extends JpaRepository<Employee, Integer> {
 @Query("SELECT e.firstName, e.lastName " + "FROM Employee e " + "WHERE e.id in :ids ")
 List<Object[]> findFirstAndLastNames(@Param(value = "ids") List<Integer> ids);
}

Step 5: Define App.java.

App.java

package com.sample.app;

import java.util.Arrays;
import java.util.List;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import com.sample.app.entity.Employee;
import com.sample.app.repository.EmployeeRepository;

@SpringBootApplication
public class App {

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

 @Bean
 public CommandLineRunner demo(EmployeeRepository empRepo) {
  return (args) -> {

   Employee emp1 = new Employee(1, "Harini", "Maj");
   Employee emp2 = new Employee(2, "Surya", "Konagandla");
   Employee emp3 = new Employee(3, "Ram", "Gunju");
   Employee emp4 = new Employee(4, "Rahim", "Khan");
   Employee emp5 = new Employee(5, "Joel", "Chelli");

   empRepo.saveAll(Arrays.asList(emp1, emp2, emp3, emp4, emp5));

   List<Object[]> emps = empRepo.findFirstAndLastNames(Arrays.asList(2, 3, 5));

   if (emps == null || emps.isEmpty())
    return;

   for (Object[] obj : emps) {
    System.out.println(obj[0] + "," + obj[1]);
   }
  };

 }

}

application.properties

logging.level.root=WARN
logging.level.org.hibernate=ERROR

## H2 specific properties
spring.h2.console.enabled=true
spring.h2.console.path=/h2

spring.datasource.url=jdbc:h2:file:~/db/myOrg.db;DB_CLOSE_ON_EXIT=FALSE;DB_CLOSE_DELAY=-1;

spring.datasource.username=krishna
spring.datasource.password=password123

spring.datasource.driverClassName=org.h2.Driver

## JPA specific properties
# Creates the schema, destroying previous data.
spring.jpa.hibernate.ddl-auto=create

spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

spring.jpa.show-sql=true
#spring.jpa.properties.hibernate.format_sql=true

## Database connection pooling properties
# Number of ms to wait before throwing an exception if no connection is available.
spring.datasource.max-wait=10000

# Maximum number of active connections that can be allocated from this pool at the same time.
spring.datasource.tomcat.max-active=10
spring.datasource.tomcat.max-idle=5
spring.datasource.tomcat.min-idle=3

Total project structure looks like below.

Run App.java, you can see below messages in console.

Surya,Konagandla

Ram,Gunju

Joel,Chelli

You can download complete working application from this link.

    

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