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Hey guys in this post, we will discuss JPA One-to-One Bi-directional mapping with Example. We will create a spring boot project step by step and connect it to the MySQL database. This is the continuation of the previous post, please follow that before proceeding with this.

Complete example

Let’s create a step-by-step spring boot project and create a bi-directional mapping between the two tables. We will create a mapping between Laptop and Brand tables.

Read More:

1. Check this how to write JPQL select query
2. Check this how to write a JPQL delete query

Watch the video

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()

Configure the datasource

spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=scbushan05
spring.datasource.password=scbushan05

spring.jpa.hibernate.ddl-auto=update

Create an entity class

Create Laptop.java inside the in.bushansirgur.springboot.entity package and add the following content

package in.bushansirgur.springboot.entity;

import java.math.BigDecimal;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

import in.bushansirgur.springboot.request.LaptopRequest;
import lombok.Getter;
import lombok.Setter;

@Entity
@Table(name="tbl_laptops")
@Getter
@Setter
public class Laptop {
	
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Long id;
	
	private String name;
	
	@OneToOne
	@JoinColumn(name = "brand_id")
	private Brand brand;
	
	private BigDecimal price;
	
	public Laptop(LaptopRequest request) {
		this.name = request.getName();
		this.price = request.getPrice(); 
	}
	
}

• @OneToOne annotation is used to add one to one relationship between two tables
• @JoinColumn annotation is used to join a new column, this will be the foreign key column of the tbl_laptops table
• @Data annotation which is a Lombok annotation, that will automatically create setters, getters, toString(), and equals() for us.
• @Entity is a mandatory annotation that indicates that this class is a JPA entity and is mapped with a database table.
• @Table annotation is an optional annotation that contains the table info like table name.

• @Id annotation is a mandatory annotation that marks a field as the primary key

Create Brand.java inside the in.bushansirgur.springboot.entity package and add the following content

package in.bushansirgur.springboot.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;

import lombok.Getter;
import lombok.Setter;

@Entity
@Table(name = "tbl_brand")
@Setter
@Getter
public class Brand {
	
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Long id;
	
	@Column(name = "brand")
	private String name;
	
	@OneToOne(mappedBy = "brand")
	private Laptop laptop;
}

• To make bi-directional, inside the Brand create a reference variable for the Laptop and add @OneToOne annotation
• We will provide the option mappedBy and the value will be the name of the reference variable of Brand inside the Laptop entity

Create a Repository

Create an interface LaptopRepository.java inside the in.bushansirgur.springboot.repos package and add the following content

package in.bushansirgur.springboot.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import in.bushansirgur.springboot.entity.Laptop;

@Repository
public interface LaptopRepository extends JpaRepository<Laptop, Long>{
	
	
}

Create an interface BrandRepository.java inside the in.bushansirgur.springboot.repos package and add the following content

package in.bushansirgur.springboot.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import in.bushansirgur.springboot.entity.Brand;

@Repository
public interface BrandRepository extends JpaRepository<Brand, Long>{

}

Create a Request class

Create a class LaptopRequest.java inside the in.bushansirgur.springboot.request package and add the following content

package in.bushansirgur.springboot.request;

import java.math.BigDecimal;

import lombok.Getter;
import lombok.Setter;

@Setter
@Getter
public class LaptopRequest {
	
	private String name;
	
	private String brand;
	
	private BigDecimal price;
	
	
}

This is just a plain old java object (POJO), contains private fields, setters, and getters. This class is used to send the JSON payload from the client.

Create a Response class

Create a class LaptopResponse.java inside the in.bushansirgur.springboot.response package and add the following content

package in.bushansirgur.springboot.response;

import java.math.BigDecimal;

import lombok.Getter;
import lombok.Setter;

@Getter
@Setter
public class LaptopResponse {
	
	private Long id;
	
	private String laptop;
	
	private BigDecimal price;
	
	private String brand;
	
}

Create a class BrandResponse.java inside the in.bushansirgur.springboot.response package and add the following content

package in.bushansirgur.springboot.response;

import java.math.BigDecimal;

import lombok.Getter;
import lombok.Setter;

@Setter
@Getter
public class BrandResponse {
	
	private Long id;
	
	private String laptop;
	
	private BigDecimal price;
	
	private String brand;
}

These are just plain old java objects (POJOs) that contain private fields, setters, and getters. These response classes are used to send the final json to the client.

Create a Rest controller

Create LaptopController.java inside the in.bushansirgur.springboot.controller package and add the following content

package in.bushansirgur.springboot.controller;

import java.util.ArrayList;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import in.bushansirgur.springboot.entity.Brand;
import in.bushansirgur.springboot.entity.Laptop;
import in.bushansirgur.springboot.repository.BrandRepository;
import in.bushansirgur.springboot.repository.LaptopRepository;
import in.bushansirgur.springboot.request.LaptopRequest;
import in.bushansirgur.springboot.response.LaptopResponse;

@RestController
public class LaptopController {
	
	@Autowired
	private LaptopRepository lRepo;
	
	@Autowired
	private BrandRepository bRepo;
	
	@GetMapping("/laptops")
	public ResponseEntity<List<LaptopResponse>> getData () {
		List<Laptop> list = lRepo.findAll();
		List<LaptopResponse> responseList = new ArrayList<>();
		list.forEach(l -> {
			LaptopResponse response = new LaptopResponse();
			response.setId(l.getId());
			response.setLaptop(l.getName());
			response.setPrice(l.getPrice());
			response.setBrand(l.getBrand().getName());
			responseList.add(response);
		});
		return new ResponseEntity<>(responseList, HttpStatus.OK);
	}
}

Create BrandController.java inside the in.bushansirgur.springboot.controller package and add the following content

package in.bushansirgur.springboot.controller;

import java.util.ArrayList;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import in.bushansirgur.springboot.entity.Brand;
import in.bushansirgur.springboot.repository.BrandRepository;
import in.bushansirgur.springboot.response.BrandResponse;

@RestController
public class BrandController {
	
	@Autowired
	private BrandRepository bRepo;
	
	@GetMapping("/brands")
	public List<BrandResponse> getAll () {
		List<Brand> list = bRepo.findAll();
		List<BrandResponse> responseList = new ArrayList<>();
		list.forEach(b -> {
			BrandResponse response = new BrandResponse();
			response.setId(b.getId());
			response.setBrand(b.getName());
			response.setLaptop(b.getLaptop().getName());
			response.setPrice(b.getLaptop().getPrice());
			responseList.add(response);
		});
		return responseList;
	}
}

Run the app

Run the application using the below maven command –

mvn spring-boot:run

Open the browser and enter the following URL –

• localhost:8080/laptops

• localhost:8080/brands

That’s it for this post, I hope you guys enjoyed this post. If you did, please share this post with your friends and colleagues. Also, share this post on your social media profile. Thanks, I will see you in the next post.