Hibernate One to Many Mapping CRUD Example

In this tutorial, we implement one-to-many bidirectional entity mapping using JPA and Hibernate, and MySQL databases. We will perform CRUD ( Create, Read, Update, and Delete) operations with the MySQL database.

The below ER diagram shows one Instructor can have many Courses and many Courses belong to one Instructor only.

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 to the below screenshot for your reference.

2. 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-bi-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>

Note that we are using mysql-connector-java driver dependency to connect the Java Hibernate application to the MySQL database:

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>

We are using Hibernate core 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>

We are using the maven-compiler-plugin to compile the Java Hibernate application with JRE 17 version:

            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>

3. Creating the JPA Entities(Persistent classes)

Let's create JPA entities that we map with database tables.

The @OneToMany and @ManyToOne JPA annotations are used to link one-to-many bidirectional entity mapping.

Instructor JPA Entity

package net.javaguides.hibernate.entity;

import java.util.List;

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;

    @OneToMany(mappedBy = "instructor", cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.DETACH,
      CascadeType.REFRESH })
    private List<Course> courses;

    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

package net.javaguides.hibernate.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "course")
public class Course {

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

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

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "instructor_id")
    private Instructor instructor;

    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;
    }

    public Instructor getInstructor() {
        return instructor;
    }

    public void setInstructor(Instructor instructor) {
        this.instructor = instructor;
    }

    @Override
    public String toString() {
        return "Course [id=" + id + ", title=" + title + "]";
    }
}

• @Table maps the entity with the table. If no @Table is defined, the default value is used: the class name of the entity.
• @Id declares the identifier property of the entity.
• @Column maps the entity's field with the table's column. If @Column is omitted, the default value is used: the field name of the entity.
• @OneToMany and @ManyToOne defines a one-to-many and many-to-one relationship between 2 entities. 
• @JoinColumn indicates the entity is the owner of the relationship: the corresponding table has a column with a foreign key to the referenced table. mappedBy indicates the entity is the inverse of the relationship.
• @Entity - This annotation specifies that the class is an entity. 
• @ManyToOne - The @ManyToOne annotation is used to specify a many-to-one database relationship.
• @OneToMany - The @OneToMany annotation is used to specify a one-to-many database relationship.
• @GeneratedValue - This annotation specifies the generation strategies for the values of primary keys.

4. Create Hibernate DAO Classes

InstructorDao.java

The InstructorDao class provides the following DAO methods for the 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

The CourseDao class provides the following DAO methods for the 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;
    }
}

5. 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/hibernate_db?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;
    }
}

6. Create the Main class and Run an Application

Let's test a one-to-many mapping as well as CRUD operations by running our Hibernate application:

package net.javaguides.hibernate;

import net.javaguides.hibernate.dao.CourseDao;
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();
        CourseDao courseDao = new CourseDao();

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

        // create some courses
        Course tempCourse1 = new Course("Air Guitar - The Ultimate Guide");
        tempCourse1.setInstructor(instructor);
        courseDao.saveCourse(tempCourse1);

        Course tempCourse2 = new Course("The Pinball Masterclass");
        tempCourse2.setInstructor(instructor);
        courseDao.saveCourse(tempCourse2);
    }
}

7. Output

8. Conclusion

In this tutorial, we successfully built a project from scratch and learned how to map a one-to-many database relationship using Hibernate 5.

We have learned how to perform CRUD operations with MySQL database using Hibernate.

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