What is the role and application of services within the Nest.js architecture?

In Nest.js, services are responsible for the application's business logic and encapsulate functionality that can be used across different parts of the application. They are typically implemented as classes with the @Injectable() decorator, which allows the use of the Dependency Injection mechanism.

Services are used for:

• Processing data and performing business operations.
• Interacting with the database through repositories or ORM.
• Encapsulating logic so that controllers remain lightweight and only handle HTTP requests.

Example of a service in Nest.js:

import { Injectable } from '@nestjs/common';

@Injectable()
export class UsersService {
  private users = [];

  findAll() {
    return this.users;
  }

  create(user) {
    this.users.push(user);
  }
}

The controller can inject this service and use its methods to handle requests.