'findTop3NBy' query method is used to retrieve top N records that match given query.
Example 1: Get top 3 records that match given firstName
List<Employee> findTop3ByFirstName(String firstName);
Above snippet produce following select query.
select * from employee e where e.first_name={FIRST_NAME} limit 3
Example 2: Get top 3 records that match to given lastName
List<Employee> findTop3ByLastName(String lastName);
Above snippet produce following select query.
select * from employee e where e.last_name={LAST_NAME} limit 3
Example 3: Get top 3 records that match to given age or firstName
List<Employee> findTop3ByAgeOrFirstName(int age, String firstName);
Above snippet produce following select query.
select * from employee 3 where 3.age={AGE} or 3.first_name={FIRST_NAME} limit 3
Example 4: Select top 3 employees matches to given firstName in the descending order of their lastName
List<Employee> findTop3ByFirstNameOrderByLastNameDesc(String firstName);
Above snippet produce following select query.
select * from employee e where e.first_name={FIRST_NAME} order by e.last_name desc limit 3
Follow below step-by-step procedure to build complete working application.
Step 1: Create new maven project ‘find-top-n-records-demo’.
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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sample.app</groupId>
<artifactId>find-top-n-records-demo</artifactId>
<version>1</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.0</version>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>
</dependencies>
</project>
Step 3: Create application.properties file under src/main/resources folder.
application.properties
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.sample.app</groupId> <artifactId>find-top-n-records-demo</artifactId> <version>1</version> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.4.0</version> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> </dependency> </dependencies> </project>
Step 4: Define Employee entity.
Employee.java
package com.sample.app.entity;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "employee")
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
@Column(name = "age")
private int age;
@Column(name = "salary")
private double salary;
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;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public static EmployeeBuilder builder() {
return new EmployeeBuilder();
}
public static class EmployeeBuilder {
private Employee emp;
public EmployeeBuilder() {
emp = new Employee();
}
public EmployeeBuilder firstName(String firstName) {
emp.setFirstName(firstName);
return this;
}
public EmployeeBuilder lastName(String lastName) {
emp.setLastName(lastName);
return this;
}
public EmployeeBuilder age(int age) {
emp.setAge(age);
return this;
}
public EmployeeBuilder salary(double salary) {
emp.setSalary(salary);
return this;
}
public Employee build() {
return emp;
}
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("Employee [id=").append(id).append(", firstName=").append(firstName).append(", lastName=")
.append(lastName).append(", age=").append(age).append(", salary=").append(salary).append("]");
return builder.toString();
}
}
Step 5: Define EmployeeRepository interface.
EmployeeRepository.java
package com.sample.app.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import com.sample.app.entity.Employee;
public interface EmployeeRepository extends JpaRepository<Employee, Integer> {
List<Employee> findTop3ByFirstName(String firstName);
List<Employee> findTop3ByLastName(String lastName);
List<Employee> findTop3ByAgeOrFirstName(int age, String firstName);
List<Employee> findTop3ByFirstNameOrderByLastNameDesc(String firstName);
}
Step 6: Define main application class.
App.java
package com.sample.app;
import java.util.List;
import javax.transaction.Transactional;
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);
}
public void printEmployees(Iterable<Employee> emps, String msg) {
System.out.println(msg);
for (Employee emp : emps) {
System.out.println(emp);
}
System.out.println();
}
@Bean
@Transactional
public CommandLineRunner demo(EmployeeRepository employeeRepository) {
return (args) -> {
Employee emp1 = Employee.builder().firstName("Ram").lastName("Gurram").age(32).salary(100000.23).build();
Employee emp2 = Employee.builder().firstName("Ram").lastName("Chelli").age(43).salary(60000).build();
Employee emp3 = Employee.builder().firstName("Gopi").lastName("Battu").age(45).salary(1000000).build();
Employee emp4 = Employee.builder().firstName("Ram").lastName("Srikanth").age(39).salary(60000).build();
Employee emp5 = Employee.builder().firstName("Surendra").lastName("Sami").age(32).salary(100000.23).build();
Employee emp6 = Employee.builder().firstName("Deeraj").lastName("Arora").age(41).salary(1000000.23).build();
Employee emp7 = Employee.builder().firstName("Sailu").lastName("Ptr").age(31).salary(50000.23).build();
Employee emp8 = Employee.builder().firstName("Loopa").lastName("Battu").age(32).salary(80000.23).build();
Employee emp9 = Employee.builder().firstName("Ram").lastName("Zlam").age(33).salary(80000.23).build();
employeeRepository.save(emp1);
employeeRepository.save(emp2);
employeeRepository.save(emp3);
employeeRepository.save(emp4);
employeeRepository.save(emp5);
employeeRepository.save(emp6);
employeeRepository.save(emp7);
employeeRepository.save(emp8);
employeeRepository.save(emp9);
List<Employee> emps = employeeRepository.findAll();
printEmployees(emps, "All the employees information");
emps = employeeRepository.findTop3ByFirstName("Ram");
printEmployees(emps, "Top 3 employees with firstName 'Ram'");
emps = employeeRepository.findTop3ByLastName("Battu");
printEmployees(emps, "Top 3 employees with lastName 'Battu'");
emps = employeeRepository.findTop3ByAgeOrFirstName(32, "Ram");
printEmployees(emps, "Top 3 employees with age 32 or firstName Ram");
emps = employeeRepository.findTop3ByFirstNameOrderByLastNameDesc("Ram");
printEmployees(emps, "Top 3 employees with name 'Ram' and order by lastName in descending order");
};
}
}
Total project structure looks like below.
Run App.java, you will see below messages in console.
All the employees information Employee [id=1, firstName=Ram, lastName=Gurram, age=32, salary=100000.23] Employee [id=2, firstName=Ram, lastName=Chelli, age=43, salary=60000.0] Employee [id=3, firstName=Gopi, lastName=Battu, age=45, salary=1000000.0] Employee [id=4, firstName=Ram, lastName=Srikanth, age=39, salary=60000.0] Employee [id=5, firstName=Surendra, lastName=Sami, age=32, salary=100000.23] Employee [id=6, firstName=Deeraj, lastName=Arora, age=41, salary=1000000.23] Employee [id=7, firstName=Sailu, lastName=Ptr, age=31, salary=50000.23] Employee [id=8, firstName=Loopa, lastName=Battu, age=32, salary=80000.23] Employee [id=9, firstName=Ram, lastName=Zlam, age=33, salary=80000.23] Top 3 employees with firstName 'Ram' Employee [id=1, firstName=Ram, lastName=Gurram, age=32, salary=100000.23] Employee [id=2, firstName=Ram, lastName=Chelli, age=43, salary=60000.0] Employee [id=4, firstName=Ram, lastName=Srikanth, age=39, salary=60000.0] Top 3 employees with lastName 'Battu' Employee [id=3, firstName=Gopi, lastName=Battu, age=45, salary=1000000.0] Employee [id=8, firstName=Loopa, lastName=Battu, age=32, salary=80000.23] Top 3 employees with age 32 or firstName Ram Employee [id=1, firstName=Ram, lastName=Gurram, age=32, salary=100000.23] Employee [id=2, firstName=Ram, lastName=Chelli, age=43, salary=60000.0] Employee [id=4, firstName=Ram, lastName=Srikanth, age=39, salary=60000.0] Top 3 employees with name 'Ram' and order by lastName in descending order Employee [id=9, firstName=Ram, lastName=Zlam, age=33, salary=80000.23] Employee [id=4, firstName=Ram, lastName=Srikanth, age=39, salary=60000.0] Employee [id=1, firstName=Ram, lastName=Gurram, age=32, salary=100000.23]
You can download complete working application from below link.
https://github.com/harikrishna553/springboot/tree/master/jpa/find-top-n-records-demo
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