In this tutorial, we will learn how to implement step by step one-to-many unidirectional entity mapping using JPA, Hibernate and MySQL database.
Overview
There are two types of one-to-many association -
- Unidirectional - In this type of association, only the source entity has a relationship field that refers to the target entity. We can navigate this type of association from one side.
- Bidirectional - In this type of association, each entity (i.e. source and target) has a relationship field that refers to each other. We can navigate this type of association from both sides.
Development Steps
- Create a Simple Maven Project
- Project Directory Structure
- POM Dependencies
- Creating the JPA Entities(Persistent classes)
- Create Hibernate DAO Classes
- Create a Hibernate configuration file - HibernateUtil.java (Java Configuration)
- Create the Main class and Run an Application
1. Create a Simple Maven Project
Use 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 a simple maven project. Refer below screenshot for your reference.
3. POM Dependencies
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-many-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>8.0.13</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.3.7.Final</version>
</dependency>
</dependencies>
<build>
<sourceDirectory>src/main/java</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
4. Creating the JPA Entities(Persistent classes)
Let's create JPA entities which we map with database tables. The @OneToMany JPA annotation is used to link one-to-many unidirectional entity mapping.
Instructor JPA Entity - Instructor.java
package net.javaguides.hibernate.entity;
import java.util.ArrayList;
import java.util.List;
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.OneToMany;
import javax.persistence.Table;
@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;
@OneToMany(cascade = CascadeType.ALL)
private List < Course > courses = new ArrayList < Course > ();
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 List < Course > getCourses() {
return courses;
}
public void setCourses(List < Course > courses) {
this.courses = courses;
}
}
Course JPA Entity - Course.java
package net.javaguides.hibernate.entity;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "course")
public class Course {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;
@Column(name = "title")
private String title;
public Course() {
}
public Course(String title) {
this.title = title;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() {
return "Course [id=" + id + ", title=" + title + "]";
}
}
5. Create Hibernate DAO Classes
InstructorDao.java
Let's create InstructorDao class add following hibernate DAO operations for Instructor entity:
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;
}
}
CourseDao.java
Let's create CourseDao class add following hibernate DAO operations for Course entity:
package net.javaguides.hibernate.dao;
import org.hibernate.Session;
import org.hibernate.Transaction;
import net.javaguides.hibernate.entity.Course;
import net.javaguides.hibernate.util.HibernateUtil;
public class CourseDao {
public void saveCourse(Course course) {
Transaction transaction = null;
try (Session session = HibernateUtil.getSessionFactory().openSession()) {
// start a transaction
transaction = session.beginTransaction();
// save the student object
session.save(course);
// commit transaction
transaction.commit();
} catch (Exception e) {
if (transaction != null) {
transaction.rollback();
}
e.printStackTrace();
}
}
public void updateCourse(Course course) {
Transaction transaction = null;
try (Session session = HibernateUtil.getSessionFactory().openSession()) {
// start a transaction
transaction = session.beginTransaction();
// save the student object
session.update(course);
// commit transaction
transaction.commit();
} catch (Exception e) {
if (transaction != null) {
transaction.rollback();
}
e.printStackTrace();
}
}
public void deleteCourse(int id) {
Transaction transaction = null;
try (Session session = HibernateUtil.getSessionFactory().openSession()) {
// start a transaction
transaction = session.beginTransaction();
// Delete a course object
Course course = session.get(Course.class, id);
if (course != null) {
session.delete(course);
System.out.println("course is deleted");
}
// commit transaction
transaction.commit();
} catch (Exception e) {
if (transaction != null) {
transaction.rollback();
}
e.printStackTrace();
}
}
public Course getCourse(int id) {
Transaction transaction = null;
Course course = null;
try (Session session = HibernateUtil.getSessionFactory().openSession()) {
// start a transaction
transaction = session.beginTransaction();
// get an course object
course = session.get(Course.class, id);
// commit transaction
transaction.commit();
} catch (Exception e) {
if (transaction != null) {
transaction.rollback();
}
e.printStackTrace();
}
return course;
}
}
6. Hibernate Utility File(Java Configuration)
Create a helper class HibernateUtil to bootstrap hibernate.
Map the Instructor and Course entities using the MetadataSources.addAnnotatedClass() method.
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/hibernate_db?useSSL=false");
settings.put(Environment.USER, "root");
settings.put(Environment.PASS, "root");
settings.put(Environment.DIALECT, "org.hibernate.dialect.MySQL5InnoDBDialect");
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.Course;
import net.javaguides.hibernate.entity.Instructor;
public class ManApp {
public static void main(String[] args) {
InstructorDao instructorDao = new InstructorDao();
Instructor instructor = new Instructor("Ramesh", "Fadatare", "ramesh@javaguides.com");
instructorDao.saveInstructor(instructor);
// create some courses
Course tempCourse1 = new Course("Learn Spring Boot");
instructor.getCourses().add(tempCourse1);
Course tempCourse2 = new Course("Learn hibernate");
instructor.getCourses().add(tempCourse2);
instructorDao.saveInstructor(instructor);
}
}
Conclusion
In this tutorial, we successfully built a project from scratch and learned how to map a one-to-one unidirectional database relationship using Hibernate/JPA.
You might also be interested in checking out the following articles on JPA and Hibernate -
Free Spring Boot Tutorial | Full In-depth Course | Learn Spring Boot in 10 Hours
Watch this course on YouTube at Spring Boot Tutorial | Fee 10 Hours Full Course