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.
<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.
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.
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.
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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