Introduction to NestJS

NestJS is a progressive Node.js framework for building efficient, reliable, and scalable server-side applications. It uses TypeScript by default and is heavily inspired by Angular, leveraging its modular architecture.

Modules

Modules are the fundamental building blocks of a NestJS application, organizing the application into cohesive blocks of functionality.

Controllers

Controllers handle incoming requests and return responses to the client. They act as the entry point for the application.

Providers

Providers are the backbone of NestJS applications, serving as a way to encapsulate the business logic. They can be services, repositories, or even factories.

To install NestJS globally, you can use the following command:

npm install -g @nestjs/cli

Then, create a new project:

nest new project-name

The typical structure of a NestJS application includes:

• src: Contains all application code.
• app.module.ts: The root module of the application.
• app.controller.ts: Handles incoming requests.
• app.service.ts: Contains business logic.

To create a basic REST API, follow these steps:

1. Generate a new controller:

nest generate controller cats

2. Generate a new service:

nest generate service cats

3. Implement the service logic in cats.service.ts:

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

@Injectable()
export class CatsService {
    private readonly cats = [];

    create(cat) {
        this.cats.push(cat);
    }

    findAll() {
        return this.cats;
    }
}

4. Implement the controller logic in cats.controller.ts:

import { Controller, Get, Post, Body } from '@nestjs/common';
import { CatsService } from './cats.service';

@Controller('cats')
export class CatsController {
    constructor(private readonly catsService: CatsService) {}

    @Post()
    create(@Body() cat) {
        this.catsService.create(cat);
    }

    @Get()
    findAll() {
        return this.catsService.findAll();
    }
}

• Use modules to encapsulate related functionality.
• Follow the Single Responsibility Principle for services and controllers.
• Utilize DTOs (Data Transfer Objects) for data validation and type safety.