In this article, you will learn about Data JPA exists projection in repository query derivation with full coding example.
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Assume that we have a scenario where we need to check whether the given email address is exists in the database before saving to the database.
We can easily achieve this by writing Data JPA query method using existsBy. To create query method in JPA, we need to create a method like this –
Boolean existsByEmail(String email);
To check the existence of an item we use the keyword exitsBy followed by the field name in which we want to check the existence. For ex: existsByName(), findByEmail() etc.,
Table of Contents
Complete example
Let’s create a step-by-step spring boot project and create query method for checking the existence of an item.
Create database and insert sample data
Open MySQL workbench and execute the following commands
CREATE DATABASE demodb;
USE demodb;
CREATE TABLE tbl_users
(
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
email VARCHAR(255) NOT NULL,
password VARCHAR(255) NOT NULL
);
INSERT INTO tbl_users(email, password) VALUES ("[email protected]", "12345");
INSERT INTO tbl_users(email, password) VALUES ("[email protected]", "12345");
We have created the table tbl_users which contains 3 fields. We have inserted the sample data as well.
Create spring boot project
There are many different ways to create a spring boot application, you can follow the below articles to create one –
>> Create spring boot application using Spring initializer
>> Create spring boot application in Spring tool suite [STS]
>> Create spring boot application in IntelliJ IDEA
Add maven dependencies
Open pom.xml and add the following dependencies –
<?xml version="1.0" encoding="UTF-8"?>
<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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.4</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>in.bushansirgur</groupId>
<artifactId>findbyfieldname</artifactId>
<version>v1</version>
<name>findbyfieldname</name>
<description>Spring boot data jpa find by field name</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
</project>
spring-boot-starter-web dependency for building web applications using Spring MVC. It uses the tomcat as the default embedded container.
spring-boot-devtools dependency for automatic reloads or live reload of applications. spring-boot-starter-data-jpa dependency is a starter for using Spring Data JPA with Hibernate. lombok dependency is a java library that will reduce the boilerplate code that we usually write inside every entity class like setters, getters, and toString()
Create an entity class
Create User.java inside the in.bushansirgur.springboot.entity package and add the following content
package in.bushansirgur.springdatajpa.entity;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Entity
@Table(name = "tbl_users")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
private String email;
private String password;
}
@Dataannotation which is a Lombok annotation, that will automatically create setters, getters, toString(), and equals() for us.@Entityis a mandatory annotation that indicates that this class is a JPA entity and is mapped with a database table.@Tableannotation is an optional annotation that contains the table info like table name.
@Idannotation is a mandatory annotation that marks a field as the primary key
Create a Repository
Create an interface UserRepository.java inside the in.bushansirgur.springboot.repos package and add the following content
package in.bushansirgur.springdatajpa.repository;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import in.bushansirgur.springdatajpa.entity.User;
@Repository
public interface UserRepository extends JpaRepository<User, Long>{
Boolean existsByEmail(String email);
}
@Repository annotates classes at the persistence layer, which will act as a database repository. We have extended this interface with JPARepository interface which will provide built-in methods to interact with the database also we can define query methods. We have defined a query method to check the existence of an email existsByEmail().
Create a Rest controller
Create UserController.java inside the in.bushansirgur.springboot.controller package and add the following content
package in.bushansirgur.springdatajpa.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
import in.bushansirgur.springdatajpa.entity.User;
import in.bushansirgur.springdatajpa.repository.UserRepository;
@RestController
public class UserController {
@Autowired
private UserRepository userRepository;
@PostMapping("/save")
public ResponseEntity<User> saveUser(@RequestBody User user) {
if (userRepository.existsByEmail(user.getEmail())) {
throw new RuntimeException("Email is already exists");
}
return new ResponseEntity<User>(userRepository.save(user), HttpStatus.CREATED);
}
}
We have autowired the UserRepository using @Autowired annotation. We have created a handler method, saveUser() which will call the repository methods save().
Run the app
Run the application using the below maven command –
mvn spring-boot:runOpen the postman and enter the following URL –
References
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