nest_provider.ts

// Users Service (Provides Business Logic)
import { Injectable } from '@nestjs/common';

// injectables include wide range of configurations such as when and how to initialise the provider
@Injectable()
export class UsersService {
  private users = ['Alice', 'Bob', 'Charlie'];

  findAll(): string[] {
    return this.users;
  }
}

// Users Controller (Depends on UsersService)
import { Controller, Get } from '@nestjs/common';
import { UsersService } from './users.service';

@Controller('users')
export class UsersController {
  constructor(private readonly usersService: UsersService) {} // Dependency Injection

  @Get()
  findAll(): string[] {
    return this.usersService.findAll(); // Uses service to get data
  }
}