Hibernate Delete or Remove an Entity Example

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In Hibernate, an entity can be removed from a database by calling the Session.delete() or Session.remove(). Using these methods, we can remove a transient or persistent object from the datastore.

This tutorial is upgraded to Hibernate framework 6 and Java 17.

Session.delete(Object object) Method

This method removes the persistent instance from the datastore. The argument may be an instance associated with the receiving Session or a transient instance with an identifier associated with an existing persistent state. This operation cascades to associated instances if the association is mapped with cascade="delete".

EntityManager.remove(Object entity)

This method removes the given entity instance from the database:

Hibernate Delete or Remove an Entity Complete Example

Let's create a Hibernate Maven application to demonstrate the usage of the Session.delete() and Session.remove() methods.

Technologies and tools used

• Hibernate 6.1.7.Final
• IDE - Eclipse
• Maven 3.5.3
• Java 17
• MySQL - 8.0.32

Development Steps

1. Create a Simple Maven Project
2. Project Directory Structure
3. Add jar Dependencies to pom.xml
4. Creating the JPA Entity Class(Persistent class)
5. Create a Hibernate configuration file - Java Configuration
6. Removing an entity using the delete() method
7. Removing an entity using the remove() method
8. 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

The project directory structure for your reference - 

3. Add jar 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-remove-entity-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 Entity Class(Persistent class)

Let's create a Student persistent class that is mapped to a database table.

A simple Persistent class should follow some rules:

• A no-arg constructor: It is recommended that you have a default constructor at least package visibility so that hibernate can create the instance of the Persistent class by newInstance() method.
• Provide an identifier property: It is better to assign an attribute as id. This attribute behaves as a primary key in a database.
• Declare getter and setter methods: The Hibernate recognizes the method by getter and setter method names by default.
• Prefer non-final class: Hibernate uses the concept of proxies, that depend on the persistent class. The application programmer will not be able to use proxies for lazy association fetching.

Create a Student entity class under net.javaguides.hibernate.entity package as follows.

package net.javaguides.hibernate.entity; import jakarta.persistence.*; @Entity @Table(name = "student") public class Student { @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; public Student() { } public Student(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; } @Override public String toString() { return "Student [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", email=" + email + "]"; } }

5. Create a Hibernate configuration file - Java Configuration

The HibernateUtil Java configuration file contains information about the database and mapping file.

HibernateUtil is a helper class to bootstrap hibernate SessionFactory.Add the Student entity to MetadataSources for mapping.

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.Student; 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(Student.class); ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder() .applySettings(configuration.getProperties()).build(); sessionFactory = configuration.buildSessionFactory(serviceRegistry); } catch (Exception e) { e.printStackTrace(); } } return sessionFactory; } }

6. Removing an entity using the delete() method

The following example deletes transient and persistent objects from the datastore using the Session.delete() method.

package net.javaguides.hibernate.dao; import org.hibernate.Session; import org.hibernate.Transaction; import net.javaguides.hibernate.entity.Student; import net.javaguides.hibernate.util.HibernateUtil; public class SessionDeleteExample { public void deleteStudent(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // Delete a persistent object Student student = session.get(Student.class, id); if (student != null) { session.delete(student); System.out.println("student 1 is deleted"); } // Delete a transient object Student student2 = new Student(); student2.setId(2); session.delete(student2); System.out.println("Student 2 is deleted"); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } }

7. Removing an entity using the remove() method

The following example deletes transient and persistent objects from the datastore using Session.remove() method.

package net.javaguides.hibernate.dao; import org.hibernate.Session; import org.hibernate.Transaction; import net.javaguides.hibernate.entity.Student; import net.javaguides.hibernate.util.HibernateUtil; public class SessionRemoveExample { public void removeStudent(int id) { Transaction transaction = null; try (Session session = HibernateUtil.getSessionFactory().openSession()) { // start a transaction transaction = session.beginTransaction(); // Delete a persistent object Student student = session.get(Student.class, id); if (student != null) { session.remove(student); System.out.println("student 1 is deleted"); } // Delete a transient object Student student2 = new Student(); student2.setId(2); session.remove(student2); System.out.println("Student 2 is deleted"); // commit transaction transaction.commit(); } catch (Exception e) { if (transaction != null) { transaction.rollback(); } e.printStackTrace(); } } }

8. Create the main App class and Run an Application

Let's test Hibernate application to connect the MySQL database.

package net.javaguides.hibernate; import net.javaguides.hibernate.dao.SessionDeleteExample; import net.javaguides.hibernate.dao.SessionRemoveExample; import net.javaguides.hibernate.dao.SessionSaveExample; import net.javaguides.hibernate.entity.Student; public class App { public static void main(String[] args) { // first save few records to database SessionSaveExample studentDao = new SessionSaveExample(); Student s1 = new Student("Ramesh", "Fadatare", "rameshfadatare@javaguides.com"); Student s2 = new Student("John", "Cena", "johncena@javaguides.com"); studentDao.saveStudent(s1); studentDao.saveStudent(s2); // delete student SessionDeleteExample deleteExample = new SessionDeleteExample(); deleteExample.deleteStudent(1); // delete second student SessionRemoveExample persistExample = new SessionRemoveExample(); persistExample.removeStudent(2); } }

Output

GitHub Repository

The complete source code of this article is available on my GitHub Repository - https://github.com/RameshMF/Hibernate-ORM-Tutorials

Conclusion

In this article, we have created a simple hibernate application to demonstrate the use of Session.delete() and Session.remove() methods.

You can learn more about Hibernate ORM Framework at Hibernate Tutorial.