JPA - @OneToOne Relationships

Overview

In One-To-One relationship, one item can belong to only one other item. It means each row of one entity is referred to one and only one row of another entity.

Let us consider the example if Employee and Department is in a reverse unidirectional manner, relation is One-To-One relation.

Creating Entities

Create a package named com.tutorialspoin.eclipselink.entity under src package if not present. Create a class named Department.java under given package. The class Department entity is shown as follows:

Department.java

package com.tutorialspoint.eclipselink.entity;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Department {

   @Id 
   @GeneratedValue( strategy=GenerationType.AUTO )
   private int id;
   private String name;

   public int getId() {
      return id;
   }

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

   public String getName( ) {
      return name;
   }

   public void setName( String deptName ) {
      this.name = deptName;
   }
}

Create the second entity in this relation Employee entity class, named Employee.java under com.tutorialspoint.eclipselink.entity package. The Employee entity class is shown as follows:

Employee.java

package com.tutorialspoint.eclipselink.entity;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.OneToOne;

@Entity
public class Employee {

   @Id
   @GeneratedValue( strategy= GenerationType.AUTO ) 	
   private int eid;
   private String ename;
   private double salary;
   private String deg;

   @OneToOne
   private Department department;

   public Employee(int eid, String ename, double salary, String deg) {
      super( );
      this.eid = eid;
      this.ename = ename;
      this.salary = salary;
      this.deg = deg;
   }

   public Employee( ) {
      super();
   }

   public int getEid( ) {
      return eid;
   }
   
   public void setEid(int eid) {
      this.eid = eid;
   }

   public String getEname( ) {
      return ename;
   }
   
   public void setEname(String ename) {
      this.ename = ename;
   }

   public double getSalary( ) {
      return salary;
   }
   
   public void setSalary(double salary) {
      this.salary = salary;
   }

   public String getDeg( ) {
      return deg;
   }
   
   public void setDeg(String deg) {
      this.deg = deg;
   }

   public Department getDepartment() {
      return department;
   }

   public void setDepartment(Department department) {
      this.department = department;
   }	
}

Persistence.xml

Persistence.xml will be created by the eclipse IDE while creating a JPA Project. The configuration details are user specifications. The persistence.xml file is shown as follows:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="3.0" xmlns="https://jakarta.ee/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://jakarta.ee/xml/ns/persistence https://jakarta.ee/xml/ns/persistence/persistence_3_0.xsd">
	<persistence-unit name="Eclipselink_JPA" transaction-type="RESOURCE_LOCAL">
	<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
	<class>com.tutorialspoint.eclipselink.entity.Employee</class>
	<class>com.tutorialspoint.eclipselink.entity.Department</class>
      <properties>
         <property name="jakarta.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jpadb"/>
         <property name="jakarta.persistence.jdbc.user" value="guest"/>
         <property name="jakarta.persistence.jdbc.password" value="guest123"/>
         <property name="jakarta.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
         <property name="eclipselink.logging.level" value="FINE"/>
         <property name="eclipselink.ddl-generation" value="create-tables"/>
      </properties>
	</persistence-unit>
</persistence>

Service Classes

This module contains the service classes, which implements the relational part using the attribute initialization. Create a package under src package named com.tutorialspoint.eclipselink.service. The DAO class named OneToOne.java is created under given package. The DAO class is shown as follows:

OneToOne.java

package com.tutorialspoint.eclipselink.service;

import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;

import com.tutorialspoint.eclipselink.entity.Department;
import com.tutorialspoint.eclipselink.entity.Employee;

public class OneToOne {
   public static void main(String[] args) {
   
   EntityManagerFactory emfactory = Persistence.createEntityManagerFactory( "Eclipselink_JPA" );
   EntityManager entitymanager = emfactory.createEntityManager( );
   entitymanager.getTransaction( ).begin( );

   //Create Department Entity
   Department department = new Department();
   department.setName("Development");

   //Store Department
   entitymanager.persist(department);

   //Create Employee Entity
   Employee employee = new Employee();
   employee.setEname("Satish");
   employee.setSalary(45000.0);
   employee.setDeg("Technical Writer");
   employee.setDepartment(department);

   //Store Employee
   entitymanager.persist(employee);

   entitymanager.getTransaction().commit();
   entitymanager.close();
   emfactory.close();
   }
}

Output

After compilation and execution of the above program you will get notifications in the console panel of Eclipse IDE. For output, check MySQL workbench as follows. In the above example two tables are created.

Pass the following query in MySQL interface and the result of department table in a tabular format is shown as follows in the query:

Select * from department

Id	Name
301	Development

Pass the following query in MySQL interface and the result of employee table in a tabular format is shown as follows in the query:

Select * from employee

Eid	Deg	                Ename	Salary	Department_id
302	Technical Writer	Satish	45000	301