Hibernate : Delete data from database

It is a two step process.

1.   Get the persisted object from database.

2.   Remove the object.

package myFirstHibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;


@Entity
public class Employee {
  @Id @GeneratedValue
  private int id;
  private String firstName;
  private String lastName;
  
  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;
  }
  
}

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>

  <session-factory>
  
    <!--  Database Connection settings -->
    <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="connection.url">jdbc:mysql://localhost/sample</property>
    <property name="connection.username">root</property>
    <property name="connection.password">tiger</property>
    
    <!-- Enable the logging of all the generated SQL statements to the console -->
    <property name="show_sql">true</property>
    
    <!-- Format the generated SQL statement to make it more readable, -->
    <property name="format_sql">false</property>
    
    <!-- Hibernate will put comments inside all generated SQL statements to hint what’s the generated SQL trying to do -->
    <property name="use_sql_comments">false</property>
    
    <!-- This property makes Hibernate generate the appropriate SQL for the chosen database. -->
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    
    <!-- Drop and re-create the database schema on startup -->
    <property name="hbm2ddl.auto">create</property>
    
    <!-- mappings for annotated classes -->
    <mapping class="myFirstHibernate.Employee" />
    
  </session-factory>
  
</hibernate-configuration>

package myFirstHibernate;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class TestEmployee {
  
  /* Step 1: Create session factory */
  private static SessionFactory getSessionFactory() {
    Configuration configuration = new Configuration().configure();
    StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().
    applySettings(configuration.getProperties());
    SessionFactory factory = configuration.buildSessionFactory(builder.build());
        return factory;
    }
  
  public static void main(String args[]){
    Employee emp1 = new Employee();
    Employee emp2 = new Employee();
    Employee emp3 = new Employee();
    
    emp1.setFirstName("Hari Krishna");
    emp1.setLastName("Gurram");
    
    emp2.setFirstName("Shreyas");
    emp2.setLastName("Desai");
    
    emp3.setFirstName("Piyush");
    emp3.setLastName("Rai");
    
    SessionFactory sessionFactory = getSessionFactory();
    Session session = sessionFactory.openSession();
    session.beginTransaction();
    
    /* Saving objects to database */
    session.save(emp1);
    session.save(emp2);
    session.save(emp3);
  
    /* Removing employee with id 1 */
    Employee emp = (Employee)session.get(Employee.class, 1);
    System.out.println(emp.getId() +" " + emp.getFirstName() + " " + emp.getLastName() +" is removed");
    session.delete(emp);
    session.getTransaction().commit();
    session.close(); 
    
  }
}

Run TesEmployee class, you will get output like below.

Hibernate: drop table if exists Employee
Hibernate: create table Employee (id integer not null auto_increment, firstName varchar(255), lastName varchar(255), primary key (id))
Dec 22, 2014 4:03:12 PM org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Hibernate: insert into Employee (firstName, lastName) values (?, ?)
Hibernate: insert into Employee (firstName, lastName) values (?, ?)
Hibernate: insert into Employee (firstName, lastName) values (?, ?)
1 Hari Krishna Gurram is removed
Hibernate: delete from Employee where id=?

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