What is NestJS?

NestJS is an advanced Node.js framework designed for building effective, reliable, and scalable server-side applications. It utilizes TypeScript, a statically typed superset of JavaScript, and draws inspiration from Angular, offering familiar patterns and structures to server-side development. Built on top of Express, a well-known Node.js web framework, NestJS can also be adapted to use Fastify for enhanced performance.

Key Features of NestJS

1. Modularity

   NestJS encourages a modular architecture, which allows developers to structure their code into distinct modules. Each module encapsulates related components such as controllers, services, and providers, thus enhancing the maintainability and scalability of the codebase.

• Modules: The fundamental units of a NestJS application, organizing code into cohesive sections.

  • Controllers: Responsible for processing incoming requests and returning responses to clients.
  • Providers: Typically represent services that handle business logic and can be injected into controllers or other services.

2. Dependency Injection

   NestJS features a robust and adaptable dependency injection system that manages the dependencies of various components, fostering loose coupling and improving testability.

• Injectable Decorator: Marks a class as a provider eligible for management by the NestJS dependency injection system.

  • Constructor Injection: Dependencies are supplied via the constructor, ensuring all necessary dependencies are available at instantiation.

3. Decorators

   Decorators in NestJS are functions that append metadata to classes, methods, properties, and parameters, extensively used for defining routes, middleware, and other configurations.

• @Controller: Designates a class as a controller capable of handling incoming HTTP requests.

  • @Get, @Post, @Put, @Delete: Specify route handlers for different HTTP methods.
  • @Injectable: Identifies a class as a provider that can be injected into other components.

4. Middleware

   Middleware functions in NestJS access the request and response objects, enabling tasks such as logging, validation, and authentication. Middleware can be applied globally, per module, or per route.

• Global Middleware: Applies to all routes in the application.

  • Module Middleware: Applies to routes within a specific module.
  • Route Middleware: Applies to designated routes.

5. Guards, Interceptors, and Pipes

   NestJS offers additional layers of functionality through guards, interceptors, and pipes.

• Guards: Implement authentication and authorization logic.

  • Interceptors: Transform or manipulate request and response data.
  • Pipes: Manage data validation and transformation.

6. Testing

   NestJS prioritizes testability, providing tools and utilities that facilitate unit tests and end-to-end testing.

• Testing Module: Enables the creation of a module instance for testing.

  • Utility Functions: Various utilities are included to assist in creating mocks and stubs.

Building an API with NestJS

To showcase the capabilities of NestJS, we will construct a simple API for managing a collection of books. This RESTful API will include endpoints for performing CRUD (Create, Read, Update, Delete) operations.

Step 1: Setting Up the Project

Start by installing the NestJS CLI globally:

npm install -g @nestjs/cli

Next, create a new project:

nest new bookstore-api

Then, navigate to the project directory:

cd bookstore-api

Step 2: Creating a Module

Generate a new module for book management:

nest generate module books

Step 3: Creating a Controller

Generate a controller for handling book-related requests:

nest generate controller books

In the generated books.controller.ts file, define the route handlers:

import { Controller, Get, Post, Body, Param, Delete, Put } from '@nestjs/common';

@Controller('books')

export class BooksController {

@Get()

findAll() {

return 'This action returns all books';

}

@Get(':id')

findOne(@Param('id') id: string) {

return This action returns a book with id: ${id};

}

@Post()

create(@Body() createBookDto: any) {

return 'This action adds a new book';

}

@Put(':id')

update(@Param('id') id: string, @Body() updateBookDto: any) {

return This action updates a book with id: ${id};

}

@Delete(':id')

remove(@Param('id') id: string) {

return This action removes a book with id: ${id};

}

}

Step 4: Creating a Service

Generate a service to manage business logic:

nest generate service books

In the generated books.service.ts file, implement the methods:

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

@Injectable()

export class BooksService {

private books = [];

findAll() {

return this.books;

}

findOne(id: string) {

return this.books.find(book => book.id === id);

}

create(book) {

this.books.push(book);

}

update(id: string, updateBookDto: any) {

const existingBook = this.findOne(id);

if (existingBook) {

// Update the book details

}

}

remove(id: string) {

this.books = this.books.filter(book => book.id !== id);

}

}

Step 5: Connecting Controller and Service

Update books.controller.ts to utilize the BooksService:

import { Controller, Get, Post, Body, Param, Delete, Put } from '@nestjs/common';

import { BooksService } from './books.service';

@Controller('books')

export class BooksController {

constructor(private readonly booksService: BooksService) {}

@Get()

findAll() {

return this.booksService.findAll();

}

@Get(':id')

findOne(@Param('id') id: string) {

return this.booksService.findOne(id);

}

@Post()

create(@Body() createBookDto: any) {

this.booksService.create(createBookDto);

}

@Put(':id')

update(@Param('id') id: string, @Body() updateBookDto: any) {

this.booksService.update(id, updateBookDto);

}

@Delete(':id')

remove(@Param('id') id: string) {

this.booksService.remove(id);

}

}

Step 6: Data Transfer Objects (DTOs)

Create Data Transfer Objects (DTOs) for validation and typing.

Generate DTOs:

nest generate class books/dto/create-book.dto --no-spec

nest generate class books/dto/update-book.dto --no-spec

Define the DTOs:

create-book.dto.ts:

export class CreateBookDto {

title: string;

author: string;

publishedDate: Date;

}

update-book.dto.ts:

import { PartialType } from '@nestjs/mapped-types';

import { CreateBookDto } from './create-book.dto';

export class UpdateBookDto extends PartialType(CreateBookDto) {}

Update books.controller.ts to incorporate DTOs:

import { Controller, Get, Post, Body, Param, Delete, Put } from '@nestjs/common';

import { BooksService } from './books.service';

import { CreateBookDto } from './dto/create-book.dto';

import { UpdateBookDto } from './dto/update-book.dto';

@Controller('books')

export class BooksController {

constructor(private readonly booksService: BooksService) {}

@Get()

findAll() {

return this.booksService.findAll();

}

@Get(':id')

findOne(@Param('id') id: string) {

return this.booksService.findOne(id);

}

@Post()

create(@Body() createBookDto: CreateBookDto) {

this.booksService.create(createBookDto);

}

@Put(':id')

update(@Param('id') id: string, @Body() updateBookDto: UpdateBookDto) {

this.booksService.update(id, updateBookDto);

}

@Delete(':id')

remove(@Param('id') id: string) {

this.booksService.remove(id);

}

}

Step 7: Adding a Database

To make the API functional, integrate a database. NestJS supports various databases through TypeORM, Mongoose, and others. For simplicity, we will use TypeORM with an SQLite database.

Install TypeORM and SQLite:

npm install @nestjs/typeorm typeorm sqlite3

Configure TypeORM in app.module.ts:

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

import { TypeOrmModule } from '@nestjs/typeorm';

import { BooksModule } from './books/books.module';

import { Book } from './books/book.entity';

@Module({

imports: [

TypeOrmModule.forRoot({

type: 'sqlite',

database: 'db.sqlite',

entities: [Book],

synchronize: true,

}),

BooksModule,

],

})

export class AppModule {}

Create the Book entity:

nest generate class books/book.entity --no-spec

Define the Book entity in book.entity.ts:

import { Entity, PrimaryGeneratedColumn, Column } from 'typeorm';

@Entity()

export class Book {

@PrimaryGeneratedColumn()

id: number;

@Column()

title: string;

@Column()

author: string;

@Column()

publishedDate: Date;

}

Update books.module.ts to include the Book entity:

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

import { TypeOrmModule } from '@nestjs/typeorm';

import { BooksService } from './books.service';

import { BooksController } from './books.controller';

import { Book } from './book.entity';

@Module({

imports: [TypeOrmModule.forFeature([Book])],

providers: [BooksService],

controllers: [BooksController],

})

export class BooksModule {}

Update books.service.ts to interact with the database:

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

import { InjectRepository } from '@nestjs/typeorm';

import { Repository } from 'typeorm';

import { Book } from './book.entity';

import { CreateBookDto } from './dto/create-book.dto';

import { UpdateBookDto } from './dto/update-book.dto';

@Injectable()

export class BooksService {

constructor(

@InjectRepository(Book)

private booksRepository: Repository<Book>,

) {}

findAll(): Promise<Book[]> {

return this.booksRepository.find();

}

findOne(id: string): Promise<Book> {

return this.booksRepository.findOne(id);

}

create(createBookDto: CreateBookDto): Promise<Book> {

const book = this.booksRepository.create(createBookDto);

return this.booksRepository.save(book);

}

async update(id: string, updateBookDto: UpdateBookDto): Promise<Book> {

await this.booksRepository.update(id, updateBookDto);

return this.booksRepository.findOne(id);

}

async remove(id: string): Promise<void> {

await this.booksRepository.delete(id);

}

}

Benefits of Using NestJS for Building APIs

1. Structured and Scalable Architecture

   The modular architecture of NestJS facilitates organized and maintainable code. By encapsulating related components within modules, developers can more effectively manage complex applications.

2. Enhanced Developer Productivity

   With built-in support for TypeScript, decorators, and dependency injection, NestJS simplifies many facets of server-side development. These features minimize boilerplate code and streamline application development and maintenance.

3. Comprehensive Testing Capabilities

   NestJS includes robust testing tools, ensuring applications are reliable and maintainable. By providing utilities for unit and end-to-end testing, NestJS aids developers in crafting high-quality software.

4. Performance and Efficiency

   NestJS, built on Express (or optionally Fastify), delivers excellent performance. Fastify, in particular, can handle numerous requests per second, making it ideal for high-performance applications.

5. Active Community and Ecosystem

   With a vibrant community and extensive ecosystem of plugins and modules, NestJS provides a supportive network that simplifies finding solutions to common issues and integrating additional functionalities.

In summary, NestJS is a formidable framework for constructing robust, scalable, and maintainable APIs. Its modular architecture, dependency injection system, and extensive use of TypeScript equip developers with the necessary tools to create efficient server-side applications. By capitalizing on the advantages of NestJS, developers can produce high-quality APIs that are easy to maintain and scale. Whether developing a small project or a large enterprise application, NestJS offers the resources needed for success in modern web development.

This first video provides an in-depth introduction to building a complete backend API using NestJS.

The second video offers a comprehensive guide on building a robust API with NestJS and Sequelize ORM, focusing on practical implementations.