JPA & HIBERNATE

What is Object Relational Mapping (ORM)?

Object Relational Mapping (ORM) is a technique that lets you use Java objects to interact with a relational database (like PostgreSQL) — without writing raw SQL.

Think of it like this:

Java (Object World)	PostgreSQL (Relational World)
`User` class	`users` table
`user.getName()`	`SELECT name FROM users`
`userRepository.save(user)`	`INSERT INTO users (...)`

ORM maps between:

Classes ↔ Tables
Fields ↔ Columns
Objects ↔ Rows

Why ORM is useful:

No need to write repetitive SQL queries
Cleaner and safer code
Database changes update Java objects automatically
Works well with frameworks like JPA and Hibernate

In Spring Boot:

We use JPA (Java Persistence API) as the standard, and Hibernate as the default ORM tool.

You write Java classes like this:

java
@Entity
public class User {
    @Id
    private Long id;
    private String name;
}