Hibernate One to One Mapping Annotation Example

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

The @OneToOne JPA annotation is used to map the source entity with the target entity.

The one-to-one association can be either unidirectional or bidirectional.  

In unidirectional association, the source entity has a relationship field that refers to the target entity and the source entity’s table contains the foreign key.

In a bidirectional association, each entity (i.e. source and target) has a relationship field that refers to each other and the target entity’s table contains the foreign key. The source entity must use the mappedBy attribute to define the bidirectional one-to-one mapping.

In this tutorial, we will implement both unidirectional and bidirectional entity mapping.

Hibernate One-to-One Unidirectional Mapping Annotation Example

In this example, we create Instructor and InstructorDetail entities and we make a one-to-one unidirectional 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

<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 unidirectional mapping, we have placed @OneToOne annotation on the Instructor entity so that the instuctor_detail_id will be created in an instructor table.

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) @JoinColumn(name = "instructor_detail_id") private InstructorDetail instructorDetail; public Instructor() { } public Instructor(String firstName, String lastName, String email) { this.firstName = firstName; this.lastName = lastName; this.email = email; } 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 String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public InstructorDetail getInstructorDetail() { return instructorDetail; } public void setInstructorDetail(InstructorDetail instructorDetail) { this.instructorDetail = instructorDetail; } }

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; public InstructorDetail() { } public InstructorDetail(String youtubeChannel, String hobby) { this.youtubeChannel = youtubeChannel; this.hobby = hobby; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getYoutubeChannel() { return youtubeChannel; } public void setYoutubeChannel(String youtubeChannel) { this.youtubeChannel = youtubeChannel; } public String getHobby() { return hobby; } public void setHobby(String hobby) { this.hobby = hobby; } }

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. Create a Hibernate configuration file - 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.Course; import net.javaguides.hibernate.entity.Instructor; /**  * 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/javafx_demo?useSSL=false"); 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(Instructor.class); configuration.addAnnotatedClass(Course.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"); instructor.setInstructorDetail(instructorDetail); InstructorDao instructorDao = new InstructorDao(); instructorDao.saveInstructor(instructor); } }

Output

Hibernate One to One Bidirectional Mapping Annotation Example

In this example, 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 InstructorDetailentities.

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

<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.

Output

Conclusion

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

You might also be interested in checking out the following articles on JPA and Hibernate -

• JPA/Hibernate One-to-One Mapping Annotation Example

• JPA/Hibernate One-to-One Bidirectional Mapping Annotation Example

• JPA Hibernate One to Many Unidirectional Mapping Example

• JPA/Hibernate One to Many Bidirectional Mapping Example

• Spring Boot Hibernate Many to Many Example

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