Dependency injection – the magic behind providers

One of NestJS’s strongest suits is its robust dependency injection (DI) system. With DI, you can easily inject one provider into another, fostering modular and maintainable code. It’s like having a sous-chef ready to assist whenever needed!

For instance, if UserService needs the capabilities of DatabaseService, here is how you can make it happen:

import { Injectable } from '@nestjs/common';
import { DatabaseService } from './database.service';
@Injectable()
export class UserService {
  constructor(
    private readonly databaseService: DatabaseService
  ) {}
  fetchUserData(): string {
    return this.databaseService.getData('user');
  }
}

In the previous code example, we have injected the capabilities of databaseService into the UserService class. This dependency needs to be injected into the constructor...