One-to-One Mapping
In One-to-One mapping, tables are associated with each other based on exactly one matching row.
We can create One-to-One mapping in three approaches.
a. Using a foreign key in either of the tables.
b. Using third table to store mapping between these two entities
c. Using Common Primary Key value in both the tables.
In this post, I am going to explain how to establish One-to-One mapping using a join table.
Let’s create two tables like below.
BANK_ACCOUNT_DETAILS
ACCOUNT_ID
|
ACCOUNT_NUMBER
|
ADDRESS
|
BRANCH
|
IFSC_CODE
|
EMPLOYEES
EMP_ID
|
FIRST_NAME
|
LAST_NAME
|
EMPLOYEE_ACCCOUNT
MY_EMP_ID
|
MY_ACCOUNT_ID
|
‘EMPLOYEE_ACCCOUNT’ is a join table, where MY_EMP_ID is a foreign key on EMPLOYEES table, and MY_ACCOUNT_ID is a foreign key on BANK_ACCOUNT_DETAILS table.
Apart from this we need to apply unique key constraints on MY_EMP_ID, MY_ACCOUNT_ID fields of EMPLOYEE_ACCOUNT table (This is require to make one to one mapping mandatory).
Entities are modelled like below.
@Entity
@Table(name = "employees")
public class Employee {
@Id
@GeneratedValue
@Column(name = "emp_id")
private int id;
private String firstName;
private String lastName;
@OneToOne(cascade = CascadeType.ALL)
@JsonManagedReference
@JoinTable(name="EMPLOYEE_ACCCOUNT", joinColumns = @JoinColumn(name="my_emp_id", referencedColumnName="emp_id"),
inverseJoinColumns = @JoinColumn(name="my_account_id", referencedColumnName="account_id"))
private SalaryAccount salaryAccount;
......
......
}
@Entity
@Table(name = "bank_account_details")
public class SalaryAccount {
@Id
@GeneratedValue
@Column(name = "account_id")
private int id;
private String accountNumber;
private String branch;
private String ifscCode;
private String address;
@JsonBackReference
@OneToOne(mappedBy = "salaryAccount")
private Employee employee;
......
......
}
Find the below working application.
Employee.java
package com.sample.app.entity;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import com.fasterxml.jackson.annotation.JsonManagedReference;
@Entity
@Table(name = "employees")
public class Employee {
@Id
@GeneratedValue
@Column(name = "emp_id")
private int id;
private String firstName;
private String lastName;
@OneToOne(cascade = CascadeType.ALL)
@JsonManagedReference
@JoinTable(name="EMPLOYEE_ACCCOUNT", joinColumns = @JoinColumn(name="my_emp_id", referencedColumnName="emp_id"),
inverseJoinColumns = @JoinColumn(name="my_account_id", referencedColumnName="account_id"))
private SalaryAccount salaryAccount;
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 SalaryAccount getSalaryAccount() {
return salaryAccount;
}
public void setSalaryAccount(SalaryAccount salaryAccount) {
this.salaryAccount = salaryAccount;
}
}
SalaryAccount.java
package com.sample.app.entity;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import com.fasterxml.jackson.annotation.JsonBackReference;
@Entity
@Table(name = "bank_account_details")
public class SalaryAccount {
@Id
@GeneratedValue
@Column(name = "account_id")
private int id;
private String accountNumber;
private String branch;
private String ifscCode;
private String address;
@JsonBackReference
@OneToOne(mappedBy = "salaryAccount")
private Employee employee;
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 Employee getEmployee() {
return employee;
}
public void setEmployee(Employee employee) {
this.employee = employee;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
EmployeeDto.java
package com.sample.app.dto;
public class EmployeeDto {
private String firstName;
private String lastName;
private SalaryAccountDto salaryAccDto;
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 SalaryAccountDto getSalaryAccDto() {
return salaryAccDto;
}
public void setSalaryAccDto(SalaryAccountDto salaryAccDto) {
this.salaryAccDto = salaryAccDto;
}
}
SalaryAccountDto.java
package com.sample.app.dto;
public class SalaryAccountDto {
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;
}
}
EmployeeRepository.java
package com.sample.app.repository;
import org.springframework.data.repository.CrudRepository;
import com.sample.app.entity.Employee;
public interface EmployeeRepository extends CrudRepository<Employee, Integer> {
}
SalaryAccountRepository.java
package com.sample.app.repository;
import org.springframework.data.repository.CrudRepository;
import com.sample.app.entity.SalaryAccount;
public interface SalaryAccountRepository extends CrudRepository<SalaryAccount, Integer> {
}
EmployeeService.java
package com.sample.app.service;
import com.sample.app.dto.EmployeeDto;
import com.sample.app.entity.Employee;
public interface EmployeeService {
Employee save(EmployeeDto emp);
Employee getById(int id);
}
SalaryAccountService.java
package com.sample.app.service;
import com.sample.app.entity.SalaryAccount;
public interface SalaryAccountService {
SalaryAccount getAccount(int id);
}
EmployeeServiceImpl.java
package com.sample.app.service.impl;
import javax.transaction.Transactional;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.sample.app.dto.EmployeeDto;
import com.sample.app.dto.SalaryAccountDto;
import com.sample.app.entity.Employee;
import com.sample.app.entity.SalaryAccount;
import com.sample.app.repository.EmployeeRepository;
import com.sample.app.service.EmployeeService;
@Service
public class EmployeeServiceImpl implements EmployeeService {
@Autowired
private EmployeeRepository empRepo;
@Override
@Transactional
public Employee save(EmployeeDto empDto) {
String firstName = empDto.getFirstName();
String lastName = empDto.getLastName();
Employee emp = new Employee();
emp.setFirstName(firstName);
emp.setLastName(lastName);
SalaryAccountDto salaryAccDto = empDto.getSalaryAccDto();
SalaryAccount salaryAccount = new SalaryAccount();
salaryAccount.setAccountNumber(salaryAccDto.getAccountNumber());
salaryAccount.setAddress(salaryAccDto.getAddress());
salaryAccount.setBranch(salaryAccDto.getBranch());
salaryAccount.setIfscCode(salaryAccDto.getIfscCode());
emp.setSalaryAccount(salaryAccount);
return empRepo.save(emp);
}
@Override
public Employee getById(int id) {
return empRepo.findById(id).get();
}
}
SalaryAccountServiceImpl.java
package com.sample.app.service.impl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.sample.app.entity.SalaryAccount;
import com.sample.app.repository.SalaryAccountRepository;
import com.sample.app.service.SalaryAccountService;
@Service
public class SalaryAccountServiceImpl implements SalaryAccountService {
@Autowired
private SalaryAccountRepository salaryAccRepo;
@Override
public SalaryAccount getAccount(int id) {
return salaryAccRepo.findById(id).get();
}
}
EmployeeController.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.EmployeeDto;
import com.sample.app.entity.Employee;
import com.sample.app.service.EmployeeService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
@RestController
@Api(tags = { "This section contains all Employee Speicifc Operations" })
public class EmployeeController {
@Autowired
private EmployeeService empService;
@ApiOperation(value = "Create new Employee", notes = "Create new Employee")
@PostMapping(value = "/employees", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Employee> saveEmployee(@RequestBody EmployeeDto empDto) {
Employee persistedEmp = empService.save(empDto);
return new ResponseEntity<>(persistedEmp, HttpStatus.CREATED);
}
@ApiOperation(value = "Get Employee", notes = "Get employee by id")
@GetMapping(value = "/employees/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Employee> getEmployees(@PathVariable final Integer id) {
Employee persistedEmp = empService.getById(id);
return new ResponseEntity<>(persistedEmp, HttpStatus.CREATED);
}
}
SalaryAccountController.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.SalaryAccount;
import com.sample.app.service.SalaryAccountService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
@RestController
@Api(tags = { "This section contains all Account Speicifc Operations" })
public class SalaryAccountController {
@Autowired
private SalaryAccountService salaryAccService;
@ApiOperation(value = "Get Account Details", notes = "Get Account Details by id")
@GetMapping(value = "/accounts/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<SalaryAccount> getAccount(@PathVariable final Integer id) {
SalaryAccount salaryAcc = salaryAccService.getAccount(id);
return new ResponseEntity<>(salaryAcc, 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>oneToOneJoinTable</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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