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Different states of an entity bean

Different states of an entity bean

Explanation

In Hibernate, an entity bean can exist in one of three states: transient, persistent, or detached. These states define the lifecycle and behavior of the entity within the context of a Hibernate session.

1.  Transient State :

  • Definition : An entity is in the transient state if it is just created using the new operator and is not associated with any Hibernate session

Characteristics

  • The entity is not stored in the database.
  • Hibernate is not aware of the entity’s existence.
  • No identifier (primary key) value is assigned unless explicitly set.

2.  Persistent State

  • Definition : An entity is in the persistent state if it is associated with a Hibernate session and is being tracked by Hibernate.
  • Characteristics :
  •  The entity is stored in the database.
  •  Any changes made to the entity are automatically synchronized with the database when the session is flushed.
  • The entity is assigned an identifier (primary key) by Hibernate.

3.  Detached State

  • Definition : An entity is in the detached state if it was previously in the persistent state but the associated session has been closed or the entity has been evicted from the session.
  • Characteristics :
  • The entity is no longer tracked by Hibernate.
  • Changes made to the entity will not be automatically synchronized with the database unless it is re-attached to a new session.      –
  • The entity retains its identifier (primary key

entity bean

Example
Example in Java:
java
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class EntityStateExample {
    public static void main(String[] args) {
        // Create SessionFactory
        SessionFactory sessionFactory = new Configuration().configure("hibernate.cfg.xml")
                .addAnnotatedClass(Student.class)
                .buildSessionFactory();

        // Transient state
        Student transientStudent = new Student("John", "Doe", "john.doe@example.com");
        
        Session session = sessionFactory.openSession();
        
        try {
            // Start transaction
            session.beginTransaction();
            
            // Persistent state
            session.save(transientStudent);
            System.out.println("Persisted: " + transientStudent);
            
            // Commit transaction
            session.getTransaction().commit();
        } finally {
            session.close();
        }
        
        // Detached state
        System.out.println("Detached: " + transientStudent);
        
        session = sessionFactory.openSession();
        
        try {
            // Start transaction
            session.beginTransaction();
            
            // Re-attach and update the entity
            transientStudent.setFirstName("Jane");
            session.update(transientStudent);
            System.out.println("Updated: " + transientStudent);
            
            // Commit transaction
            session.getTransaction().commit();
        } finally {
            session.close();
            sessionFactory.close();
        }
    }
}

@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;

    // Constructors
    public Student() {}
    public Student(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    // Getters and setters
    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 + "]";
    }
}

Example of Different states of an entity bean

  • The Student object transientStudent starts in the transient state.
  • After being saved in the session, it moves to the persistent state.
  • When the session is closed, it moves to the detached state.
  • The detached entity is then re-attached and updated in a new session.

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