Hibernate 5 – Delete or Remove an Entity Example

Hibernate 5 – Delete or Remove an Entity Example

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”.

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.ducatindia.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>

Creating the JPA Entity Class(Persistent class)

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.

packagenet.ducatindia.hibernate.entity;

importjavax.persistence.Column;
importjavax.persistence.Entity;
importjavax.persistence.GeneratedValue;
importjavax.persistence.GenerationType;
importjavax.persistence.Id;
importjavax.persistence.Table;

@Entity
@Table(name="student")
publicclassStudent {

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

@Column(name="first_name")
privateStringfirstName;

@Column(name="last_name")
privateStringlastName;

@Column(name="email")
privateString email;

publicStudent() {

    }

publicStudent(StringfirstName, StringlastName, Stringemail) {
this.firstName=firstName;
this.lastName=lastName;
this.email= email;
    }

publicintgetId() {
return id;
    }

publicvoidsetId(intid) {
this.id = id;
    }

publicStringgetFirstName() {
returnfirstName;
    }

publicvoidsetFirstName(StringfirstName) {
this.firstName=firstName;
    }

publicStringgetLastName() {
returnlastName;
    }

publicvoidsetLastName(StringlastName) {
this.lastName=lastName;
    }

publicStringgetEmail() {
return email;
    }

publicvoidsetEmail(Stringemail) {
this.email= email;
    }

@Override
publicStringtoString() {
return"Student [id="+ id +", firstName="+firstName+", lastName="+lastName+", email="+ email +"]";
    }
}

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.

packagenet.ducatindia.hibernate.util;

importjava.util.Properties;

importorg.hibernate.SessionFactory;
importorg.hibernate.boot.registry.StandardServiceRegistryBuilder;
importorg.hibernate.cfg.Configuration;
importorg.hibernate.cfg.Environment;
importorg.hibernate.service.ServiceRegistry;

importnet.ducatindia.hibernate.entity.Student;

publicclassHibernateUtil {
privatestaticSessionFactorysessionFactory;
publicstaticSessionFactorygetSessionFactory() {
if (sessionFactory==null) {
try {
Configurationconfiguration=newConfiguration();

// Hibernate settings equivalent to hibernate.cfg.xml's properties
Properties settings =newProperties();
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);

ServiceRegistryserviceRegistry=newStandardServiceRegistryBuilder()
                    .applySettings(configuration.getProperties()).build();

sessionFactory=configuration.buildSessionFactory(serviceRegistry);
            } catch (Exception e) {
e.printStackTrace();
            }
        }
returnsessionFactory;
    }
}

Removing an entity using delete() method

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

packagenet.ducatindia.hibernate.dao;

importorg.hibernate.Session;
importorg.hibernate.Transaction;

importnet.ducatindia.hibernate.entity.Student;
importnet.ducatindia.hibernate.util.HibernateUtil;

publicclassSessionDeleteExample {
publicvoiddeleteStudent(intid) {
Transactiontransaction=null;
try (Sessionsession=HibernateUtil.getSessionFactory().openSession()) {
// start a transaction
transaction=session.beginTransaction();

// Delete a persistent object
Studentstudent=session.get(Student.class, id);
if (student !=null) {
session.delete(student);
System.out.println("student 1 is deleted");
            }

// Delete a transient object
Student student2 =newStudent();
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();
        }
    }
}

Removing an entity using remove() method

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

packagenet.ducatindia.hibernate.dao;

importorg.hibernate.Session;
importorg.hibernate.Transaction;

importnet.ducatindia.hibernate.entity.Student;
importnet.ducatindia.hibernate.util.HibernateUtil;

publicclassSessionRemoveExample {
publicvoidremoveStudent(intid) {
Transactiontransaction=null;
try (Sessionsession=HibernateUtil.getSessionFactory().openSession()) {
// start a transaction
transaction=session.beginTransaction();

// Delete a persistent object
Studentstudent=session.get(Student.class, id);
if (student !=null) {
session.remove(student);
System.out.println("student 1 is deleted");
            }

// Delete a transient object
Student student2 =newStudent();
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();
        }
    }
}

Create the main App class and Run an Application

Let’s test Hibernate application to connect MySQL database.

packagenet.ducatindia.hibernate;

importnet.ducatindia.hibernate.dao.SessionDeleteExample;
importnet.ducatindia.hibernate.dao.SessionRemoveExample;
importnet.ducatindia.hibernate.dao.SessionSaveExample;
importnet.ducatindia.hibernate.entity.Student;

publicclassApp {
publicstaticvoidmain(String[] args) {

// first save few records to database
SessionSaveExamplestudentDao=newSessionSaveExample();
Student s1 =newStudent("Rajan", "Mishra", "rajanmishra@ducatindia.com");
Student s2 =newStudent("Ram", "Mishra", "rammishra@ducatindia.com");
studentDao.saveStudent(s1);
studentDao.saveStudent(s2);

// delete student
SessionDeleteExampledeleteExample=newSessionDeleteExample();
deleteExample.deleteStudent(1);

// delete second student
SessionRemoveExamplepersistExample=newSessionRemoveExample();
persistExample.removeStudent(2);
    }
}

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