Many-to-One Relationship in Spring Boot Data JPA

 Many-to-One Relationship in Spring Boot Data JPA

For Explanation Watch video :: 

pom.xml

<?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>2.6.6</version>

<relativePath/> <!-- lookup parent from repository -->

</parent>

<groupId>com.app</groupId>

<artifactId>SpringBootManyToOne</artifactId>

<version>0.0.1-SNAPSHOT</version>

<name>SpringBootManyToOne</name>

<description>Demo project for Spring Boot</description>

<properties>

<java.version>11</java.version>

</properties>

<dependencies>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-data-jpa</artifactId>

</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>

application.properties

#datsource 

spring.datasource.url=jdbc:mysql://localhost:3306/new

spring.datasource.username=root

spring.datasource.password=root

#jpa

spring.jpa.show-sql=true

spring.jpa.hibernate.ddl-auto=create

SpringBootManyToOneApplication 

package com.app;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication

public class SpringBootManyToOneApplication {

public static void main(String[] args) {

SpringApplication.run(SpringBootManyToOneApplication.class, args);

}

}

Book

package com.app.entity;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

import lombok.AllArgsConstructor;

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@AllArgsConstructor

@NoArgsConstructor

@Entity

@Table(name = "bktab")

public class Book {

@Id

private Integer bid;

private String bname;

}

Student 

package com.app.entity;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

import lombok.AllArgsConstructor;

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@NoArgsConstructor

@AllArgsConstructor

@Entity

@Table(name = "stdtab")

public class Student {

@Id

private Integer sid;

private String sname;

@ManyToOne

@JoinColumn(name = "bidFk")

private Book bob;

}

BookRepository 

package com.app.repo;

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

import com.app.entity.Book;

public interface BookRepository extends JpaRepository<Book, Integer>{

}

StudentRepository 

package com.app.repo;

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

import com.app.entity.Student;

public interface StudentRepository extends JpaRepository<Student, Integer>{

}

TestRunner 

package com.app.runner;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.boot.CommandLineRunner;

import org.springframework.stereotype.Component;

import com.app.entity.Book;

import com.app.entity.Student;

import com.app.repo.BookRepository;

import com.app.repo.StudentRepository;

@Component

public class TestRunner implements CommandLineRunner{

@Autowired

private BookRepository brepo;

@Autowired

private StudentRepository srepo;

@Override

public void run(String... args) throws Exception {

//create the book obj

Book bk1 = new Book(101,"DS");

Book bk2 = new Book(102,"SB");

//save this

brepo.save(bk1);

brepo.save(bk2);

//create Student

Student st1 = new Student(50,"SAM",bk1);

Student st2 = new Student(60,"JHON",bk1);

Student st3 = new Student(70,"ANGELA",bk2);

Student st4 = new Student(80,"BROCK",bk2);

srepo.save(st1);

srepo.save(st2);

srepo.save(st3);

srepo.save(st4);

}

}