JPA/Hibernate One to One Bidirectional Mapping Annotation Example

In this tutorial, we will learn how to implement step-by-step one-to-one bidirectional entity mapping using JPA, Hibernate, and the MySQL database.

In this example, we create Instructor and InstructorDetail entities and we make a one-to-one mapping between them.

We will implement CRUD (create/save, read, update, delete) operations for Instructor and InstructorDetail entities.

For Instructor DAO CRUD operations:

void saveInstructor(Instructor instructor);

void updateInstructor(Instructor instructor);

void deleteInstructor(int id);

Instructor getInstructor(int id);
        

For InstructorDetailDao DAO CRUD operations:

void saveInstructorDetail(InstructorDetail instructorDetail);

void updateInstructorDetail(InstructorDetail instructorDetail);

InstructorDetail getInstructorDetail(int id);

Development Steps

1. Create a Simple Maven Project
2. Project Directory Structure
3. Add jar Dependencies to pom.xml
4. Creating the JPA Entities(Persistent classes)
5. Create Hibernate DAO Classes
6. Create a Hibernate configuration file - HibernateUtil.java (Java Configuration)
7. Create the Main class and Run an Application

1. Create a Simple Maven Project

Use the How to Create a Simple Maven Project in Eclipse article to create a simple Maven project in Eclipse IDE.

2. Project Directory Structure

Let's create a packaging structure for the above-created simple maven project. Refer below screenshot for your reference.

3. Add dependencies to pom.xml

We are using MySQL database so add MySQL dependency to 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>
    <parent>
        <groupId>net.javaguides.hibernate</groupId>
        <artifactId>hibernate-tutorial</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <artifactId>hibernate-one-to-one-example</artifactId>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>6.1.7.Final</version>
        </dependency>
    </dependencies>
    <build>
        <sourceDirectory>src/main/java</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>
    

4. Creating the JPA Entities(Persistent classes)

We are creating a bidirectional mapping, we have placed @OneToOne annotation on both entity classes.

Instructor JPA Entity

package net.javaguides.hibernate.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "instructor")
public class Instructor {

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

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email")
    private String email;

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "instructor", fetch = FetchType.LAZY)
    private InstructorDetail instructorDetail;

    public Instructor() {

    }

    public Instructor(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }
   // getters and setters
}

InstructorDetail JPA Entity

package net.javaguides.hibernate.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "instructor_detail")
public class InstructorDetail {

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

    @Column(name = "youtube_channel")
    private String youtubeChannel;

    @Column(name = "hobby")
    private String hobby;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "instructor_id")
    private Instructor instructor;

    public InstructorDetail() {

    }

    public InstructorDetail(String youtubeChannel, String hobby) {
        this.youtubeChannel = youtubeChannel;
        this.hobby = hobby;
    }
    // getters and setters
}

5. Create Hibernate DAO Classes

InstructorDao.java

package net.javaguides.hibernate.dao;

import org.hibernate.Session;
import org.hibernate.Transaction;

import net.javaguides.hibernate.entity.Instructor;
import net.javaguides.hibernate.util.HibernateUtil;

public class InstructorDao {
    public void saveInstructor(Instructor instructor) {
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // save the student object
            session.save(instructor);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }

    public void updateInstructor(Instructor instructor) {
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // save the student object
            session.update(instructor);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }

    public void deleteInstructor(int id) {

        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();

            // Delete a instructor object
            Instructor instructor = session.get(Instructor.class, id);
            if (instructor != null) {
                session.delete(instructor);
                System.out.println("instructor is deleted");
            }

            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }

    public Instructor getInstructor(int id) {

        Transaction transaction = null;
        Instructor instructor = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // get an instructor object
            instructor = session.get(Instructor.class, id);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
        return instructor;
    }
}
    

InstructorDetailDao.java

package net.javaguides.hibernate.dao;

import org.hibernate.Session;
import org.hibernate.Transaction;

import net.javaguides.hibernate.entity.InstructorDetail;
import net.javaguides.hibernate.util.HibernateUtil;

public class InstructorDetailDao {

    public void saveInstructorDetail(InstructorDetail instructorDetail) {
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // save the student object
            session.save(instructorDetail);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }

    public void updateInstructorDetail(InstructorDetail instructorDetail) {
        Transaction transaction = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // save the student object
            session.update(instructorDetail);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
    }

    public InstructorDetail getInstructorDetail(int id) {

        Transaction transaction = null;
        InstructorDetail instructor = null;
        try (Session session = HibernateUtil.getSessionFactory().openSession()) {
            // start a transaction
            transaction = session.beginTransaction();
            // get an instructor object
            instructor = session.get(InstructorDetail.class, id);
            // commit transaction
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }
        return instructor;
    }
}
        

6. HibernateUtil.java (Java Configuration)

The HibernateUtil Java configuration file contains information about the database and mapping file. Let's create a HibernateUtil file and write the following code in it.

package net.javaguides.hibernate.util;

import java.util.Properties;

import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.cfg.Environment;
import org.hibernate.service.ServiceRegistry;

import net.javaguides.hibernate.entity.Instructor;
import net.javaguides.hibernate.entity.InstructorDetail;

/**
 * Java based configuration
 * @author ramesh Fadatare
 *
 */
public class HibernateUtil {
    private static SessionFactory sessionFactory;

    public static SessionFactory getSessionFactory() {
        if (sessionFactory == null) {
            try {
                Configuration configuration = new Configuration();

                // Hibernate settings equivalent to hibernate.cfg.xml's properties
                Properties settings = new Properties();
                settings.put(Environment.DRIVER, "com.mysql.cj.jdbc.Driver");
                settings.put(Environment.URL, "jdbc:mysql://localhost:3306/hibernate_db");
                settings.put(Environment.USER, "root");
                settings.put(Environment.PASS, "root");
                settings.put(Environment.SHOW_SQL, "true");

                settings.put(Environment.CURRENT_SESSION_CONTEXT_CLASS, "thread");

                settings.put(Environment.HBM2DDL_AUTO, "create-drop");

                configuration.setProperties(settings);
                configuration.addAnnotatedClass(InstructorDetail.class);
                configuration.addAnnotatedClass(Instructor.class);

                ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
                    .applySettings(configuration.getProperties()).build();
                System.out.println("Hibernate Java Config serviceRegistry created");
                sessionFactory = configuration.buildSessionFactory(serviceRegistry);
                return sessionFactory;

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return sessionFactory;
    }
}

7. Create the Main class and Run an Application

package net.javaguides.hibernate;

import net.javaguides.hibernate.dao.InstructorDao;
import net.javaguides.hibernate.entity.Instructor;
import net.javaguides.hibernate.entity.InstructorDetail;

public class ManApp {
    public static void main(String[] args) {

        Instructor instructor = new Instructor("Ramesh", "Fadatare", "ramesh@javaguides.com");

        InstructorDetail instructorDetail = new InstructorDetail("http://www.youtube.com", "Guitar");
        // associate the objects
        instructorDetail.setInstructor(instructor);
        // associate the objects
        instructor.setInstructorDetail(instructorDetail);

        // when you get instructorDetail then hibernate also saves instructor info
        InstructorDao instructorDao = new InstructorDao();
        instructorDao.saveInstructor(instructor);
    }
}

Note that when you save instructorDetail then hibernate also saves instructor info because of cascade and bidirectional.

Conclusion

In this tutorial, we successfully built a Hibernate project from scratch and learned how to map a one-to-one bidirectional database relationship using Hibernate/JPA.