ORM & JPA Introduction

What is ORM?

ORM (Object-Relational Mapping) maps Java objects to database tables automatically.

Without ORM (Plain JDBC)

String sql = "INSERT INTO users (name, email) VALUES (?, ?)";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, user.getName());
stmt.setString(2, user.getEmail());
stmt.executeUpdate();

With ORM (JPA)

entityManager.persist(user); // That's it!

JPA (Java Persistence API)

JPA is a specification for ORM in Java. Hibernate is the most popular implementation.

Entity Class

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @Column(name = "name")
    private String name;
    
    @Column(name = "email", unique = true)
    private String email;
    
    // Getters and setters
}

CRUD Operations

// Create
User user = new User();
user.setName("Alice");
user.setEmail("alice@example.com");
entityManager.persist(user);

// Read
User found = entityManager.find(User.class, 1L);

// Update
found.setName("Alice Updated");
entityManager.merge(found);

// Delete
entityManager.remove(found);

Benefits of ORM

Quiz