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 datastore.
The following snappits or examples demonstrate the use of Session.delete() and Session.remove() methods.
Session.delete(Object object) Method
Remove a 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 existing persistent state. This operation cascades to associated instances if the association is mapped with cascade="delete".
EntityManager.remove(Object entity)
Remove the entity instance.
In this article, we will JPA annotations for mapping between Student Java class and database table.
Technologies and tools used
- Hibernate 5.3.7.Final
- IDE - Eclipse Noen
- Maven 3.5.3
- JavaSE 1.8
- MySQL - 8.0.13
Let's start developing step by step Hibernate application using Maven as project management and build tool.
Development Steps
- Create a Simple Maven Project
- Project Directory Structure
- Add jar Dependencies to pom.xml
- Creating the JPA Entity Class(Persistent class)
- Create a Hibernate configuration file - Java Configuration
- Removing an entity using delete() method
- Removing an entity using remove() method
- 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 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>8.0.13</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 Entity Class(Persistent class)
Let's create a Student persistent class that are 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 depends 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 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 = "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.DIALECT, "org.hibernate.dialect.MySQL5Dialect");
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 delete() method
The following example deletes transient and persistent objects from datastore using 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 remove() method
The following example deletes transient and persistent objects from 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 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 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
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