Spring jpa: One to Many Mapping using a foreign key

It is a relationship between two tables where a row from one table can have multiple matching rows in another table.

For example, let’s take USERS and BANK_ACCOUNT_DETAILS tables. One user can have multiple bank accounts, but a bank account always associated with one user.

USERS table defined like below.

USER_ID	FIRST_NAME	LAST_NAME

BANK_ACCOUNT_DETAILS defined like below.

ACCOUNT_ID	ACCOUNT_NUMBER	ADDRESS	BRANCH	IFSC_CODE	MY_USER_ID

MY_USER_ID is a foreign key that refers to USER_ID column of USERS table.

Entities are modelled like below.

@Entity
@Table(name = "USERS")
public class User {
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 @Column(name = "USER_ID")
 private int id;
 
 @Column(name = "FIRST_NAME")
 private String firstName;
 
 @Column(name = "LAST_NAME")
 private String lastName;

 @OneToMany(cascade = CascadeType.ALL)
 @JoinColumn(name = "MY_USER_ID")
 @JsonManagedReference
 private Set<BankAccount> bankAccounts;

 ......
 ......
}

@Entity
@Table(name = "BANK_ACCOUNT_DETAILS")
public class BankAccount {

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 @Column(name = "ACCOUNT_ID")
 private int id;

 @Column(name = "ACCOUNT_NUMBER")
 private String accountNumber;
 
 @Column(name = "BRANCH")
 private String branch;
 
 @Column(name = "IFSC_CODE")
 private String ifscCode;

 @Column(name = "ADDRESS")
 private String address;

 @JsonBackReference
 @ManyToOne
 @JoinColumn(name = "MY_USER_ID")
 private User user;

 ......
 ......
}

Find the below working application.

User.java

package com.sample.app.entity;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonManagedReference;

@Entity
@Table(name = "USERS")
public class User {
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 @Column(name = "USER_ID")
 private int id;
 
 @Column(name = "FIRST_NAME")
 private String firstName;
 
 @Column(name = "LAST_NAME")
 private String lastName;

 @OneToMany(cascade = CascadeType.ALL)
 @JoinColumn(name = "MY_USER_ID")
 @JsonManagedReference
 private Set<BankAccount> bankAccounts;

 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 Set<BankAccount> getBankAccounts() {
  return bankAccounts;
 }

 public void setBankAccounts(Set<BankAccount> bankAccounts) {
  this.bankAccounts = bankAccounts;
 }

}

BankAccount.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.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonBackReference;

@Entity
@Table(name = "BANK_ACCOUNT_DETAILS")
public class BankAccount {

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 @Column(name = "ACCOUNT_ID")
 private int id;

 @Column(name = "ACCOUNT_NUMBER")
 private String accountNumber;
 
 @Column(name = "BRANCH")
 private String branch;
 
 @Column(name = "IFSC_CODE")
 private String ifscCode;

 @Column(name = "ADDRESS")
 private String address;

 @JsonBackReference
 @ManyToOne
 @JoinColumn(name = "MY_USER_ID")
 private User user;

 public String getAccountNumber() {
  return accountNumber;
 }

 public void setAccountNumber(String accountNumber) {
  this.accountNumber = accountNumber;
 }

 public String getBranch() {
  return branch;
 }

 public void setBranch(String branch) {
  this.branch = branch;
 }

 public String getIfscCode() {
  return ifscCode;
 }

 public void setIfscCode(String ifscCode) {
  this.ifscCode = ifscCode;
 }

 public String getAddress() {
  return address;
 }

 public void setAddress(String address) {
  this.address = address;
 }

 public User getUser() {
  return user;
 }

 public void setUser(User user) {
  this.user = user;
 }

 public int getId() {
  return id;
 }

 public void setId(int id) {
  this.id = id;
 }

}

BankAccountDto.java

package com.sample.app.dto;

public class BankAccountDto {
 private String accountNumber;
 private String branch;
 private String ifscCode;
 private String address;

 public String getAccountNumber() {
  return accountNumber;
 }

 public void setAccountNumber(String accountNumber) {
  this.accountNumber = accountNumber;
 }

 public String getBranch() {
  return branch;
 }

 public void setBranch(String branch) {
  this.branch = branch;
 }

 public String getIfscCode() {
  return ifscCode;
 }

 public void setIfscCode(String ifscCode) {
  this.ifscCode = ifscCode;
 }

 public String getAddress() {
  return address;
 }

 public void setAddress(String address) {
  this.address = address;
 }

}

UserDto.java

package com.sample.app.dto;

import java.util.List;

public class UserDto {
 private String firstName;
 private String lastName;
 private List<BankAccountDto> accounts;

 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 List<BankAccountDto> getAccounts() {
  return accounts;
 }

 public void setAccounts(List<BankAccountDto> accounts) {
  this.accounts = accounts;
 }

 

}

BankAccountRepository.java

package com.sample.app.repository;

import org.springframework.data.repository.CrudRepository;

import com.sample.app.entity.BankAccount;

public interface BankAccountRepository extends CrudRepository<BankAccount, Integer> {

}

UserRepository.java

package com.sample.app.repository;

import org.springframework.data.repository.CrudRepository;

import com.sample.app.entity.User;

public interface UserRepository extends CrudRepository<User, Integer> {

}

BankAccountService.java

package com.sample.app.service;

import com.sample.app.entity.BankAccount;

public interface BankAccountService {
 
 BankAccount getAccount(int id);

}

UserService.java

package com.sample.app.service;

import com.sample.app.dto.UserDto;
import com.sample.app.entity.User;

public interface UserService {

 User save(UserDto emp);

 User getById(int id);

}

BankAccountServiceImpl.java

package com.sample.app.service.impl;

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

import com.sample.app.entity.BankAccount;
import com.sample.app.repository.BankAccountRepository;
import com.sample.app.service.BankAccountService;

@Service
public class BankAccountServiceImpl implements BankAccountService {

 @Autowired
 private BankAccountRepository salaryAccRepo;

 @Override
 public BankAccount getAccount(int id) {
  return salaryAccRepo.findById(id).get();
 }

}

UserServiceImpl.java

package com.sample.app.service.impl;

import java.util.HashSet;
import java.util.List;
import java.util.Set;

import javax.transaction.Transactional;

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

import com.sample.app.dto.BankAccountDto;
import com.sample.app.dto.UserDto;
import com.sample.app.entity.BankAccount;
import com.sample.app.entity.User;
import com.sample.app.repository.UserRepository;
import com.sample.app.service.UserService;

@Service
public class UserServiceImpl implements UserService {

 @Autowired
 private UserRepository userRepo;

 @Override
 @Transactional
 public User save(UserDto empDto) {

  String firstName = empDto.getFirstName();

  String lastName = empDto.getLastName();

  User emp = new User();
  emp.setFirstName(firstName);
  emp.setLastName(lastName);

  List<BankAccountDto> bankAccountsDto = empDto.getAccounts();

  Set<BankAccount> accounts = new HashSet<>();

  for (BankAccountDto accDto : bankAccountsDto) {
   BankAccount bankAccount = new BankAccount();
   bankAccount.setAccountNumber(accDto.getAccountNumber());
   bankAccount.setAddress(accDto.getAddress());
   bankAccount.setBranch(accDto.getBranch());
   bankAccount.setIfscCode(accDto.getIfscCode());

   accounts.add(bankAccount);
  }

  emp.setBankAccounts(accounts);

  return userRepo.save(emp);
 }

 @Override
 public User getById(int id) {
  return userRepo.findById(id).get();
 }

}

AccountController.java

package com.sample.app.controller;

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

import com.sample.app.entity.BankAccount;
import com.sample.app.service.BankAccountService;

import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;

@RestController
@Api(tags = { "This section contains all Account Speicifc Operations" })
public class AccountController {

 @Autowired
 private BankAccountService salaryAccService;

 @ApiOperation(value = "Get Account Details", notes = "Get Account Details by id")
 @GetMapping(value = "/accounts/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
 public ResponseEntity<BankAccount> getAccount(@PathVariable final Integer id) {

  BankAccount salaryAcc = salaryAccService.getAccount(id);

  return new ResponseEntity<>(salaryAcc, HttpStatus.CREATED);
 }
}

UserController.java

package com.sample.app.controller;

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

import com.sample.app.dto.UserDto;
import com.sample.app.entity.User;
import com.sample.app.service.UserService;

import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;

@RestController
@Api(tags = { "This section contains all user Speicifc Operations" })
public class UserController {

 @Autowired
 private UserService userService;

 @ApiOperation(value = "Create new user", notes = "Create new user")
 @PostMapping(value = "/users", produces = MediaType.APPLICATION_JSON_VALUE)
 public ResponseEntity<User> saveEmployee(@RequestBody UserDto empDto) {

  User persistedEmp = userService.save(empDto);

  return new ResponseEntity<>(persistedEmp, HttpStatus.CREATED);
 }

 @ApiOperation(value = "Get user", notes = "Get user by id")
 @GetMapping(value = "/users/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
 public ResponseEntity<User> getEmployees(@PathVariable final Integer id) {

  User persistedEmp = userService.getById(id);

  return new ResponseEntity<>(persistedEmp, HttpStatus.CREATED);
 }

}

SwaggerConfig.java

package com.sample.app.config;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.service.ApiInfo;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.swagger2.annotations.EnableSwagger2;

@Component
@EnableAutoConfiguration
@EnableSwagger2
public class SwaggerConfig {

 @Bean
 public Docket userApi() {

  return new Docket(DocumentationType.SWAGGER_2).apiInfo(apiInfo()).select().paths(PathSelectors.any())
    .apis(RequestHandlerSelectors.basePackage("com.sample.app.controller")).build();
 }

 private ApiInfo apiInfo() {

  return new ApiInfoBuilder().title("Query builder").description("Query builder using spring specification")
    .version("2.0").build();
 }
}

App.java

package com.sample.app;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App {

 public static void main(String args[]) {
  SpringApplication.run(App.class, args);
 }

}

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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>com.sample.app</groupId>
 <artifactId>oneToManyForeignKey</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>

  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
  </dependency>

  <dependency>
   <groupId>io.springfox</groupId>
   <artifactId>springfox-swagger2</artifactId>
   <version>2.9.2</version>
  </dependency>


  <dependency>
   <groupId>io.springfox</groupId>
   <artifactId>springfox-swagger-ui</artifactId>
   <version>2.9.2</version>
  </dependency>

 </dependencies>
</project>

Create application.properties file under src/main/resources folder.

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

spring.jackson.serialization.FAIL_ON_EMPTY_BEANS=false

Total project structure looks like below.

Run App.java.

Open swagger url 'http://localhost:8080/swagger-ui.html' in browser to interact with the REST services.

Open the url 'http://localhost:8080/h2/login.do' to see H2 console.

You can download complete working application from this link.

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