Nest JS Tutorial: A Comprehensive Guide to Building Scalable Applications

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Introduction

In this Nest JS tutorial, we will guide you through the process of building robust, scalable server-side applications using Nest JS. Nest JS is a progressive Node.js framework that leverages TypeScript to create efficient and reliable applications. Its modular architecture and strong typing capabilities make it an excellent choice for building enterprise-level applications.

Also, Read: Complete Next.js Tutorial: Mastering Full Stack Development

Overview of Nest JS

Nest JS is built on top of Express.js (or optionally Fastify) and provides an out-of-the-box application architecture. This architecture allows for the effortless creation of highly testable, scalable, loosely coupled, and easily maintainable applications. Learn more about Nest JS.

Importance and Benefits of Learning Nest JS

  • TypeScript Support: Provides a strongly typed programming language which enhances code quality and maintainability.
  • Modular Architecture: Encourages the separation of concerns and scalability.
  • Extensive Ecosystem: Integrates seamlessly with other libraries and technologies like TypeORM, Mongoose, and GraphQL.
  • Community and Documentation: Strong community support and comprehensive documentation make learning and using Nest JS easier.

Structure and Objectives of This Nest JS Tutorial

This Nest JS tutorial is designed for beginners and covers the following:

  1. Setting up the development environment.
  2. Creating a basic Nest JS application.
  3. Understanding core concepts like modules, controllers, and providers.
  4. Building a RESTful API.
  5. Connecting to a database.
  6. Implementing authentication and authorization.
  7. Handling errors and validation.
  8. Testing and deploying the application.
  9. Exploring advanced topics and integrations.

By the end of this tutorial, you will have a solid understanding of Nest JS and the ability to build and deploy your own applications. For more information, refer to the official Nest JS documentation.

Setting Up Your Development Environment

Before we dive into building our application, we need to set up our development environment. This step is crucial to ensure that everything runs smoothly as we follow along with this Nest JS tutorial.

Prerequisites

  • A computer with a modern operating system (Windows, macOS, or Linux)
  • A basic understanding of JavaScript and TypeScript
  • Node.js and npm installed on your machine

Installing Node.js and npm

First, we need to install Node.js and npm (Node Package Manager). You can download the installer from the official Node.js website. Follow the instructions to complete the installation.

Installing Nest JS CLI

Next, we will install the Nest JS CLI, which will help us to generate and manage our Nest JS applications. Open your terminal and run the following command:

npm install -g @nestjs/cli

You can find more information about the Nest JS CLI on the official documentation.

Configuring Your IDE for Nest JS Development

For an optimal development experience, it’s recommended to use an IDE like Visual Studio Code (VS Code). Install the recommended extensions for JavaScript/TypeScript development, such as the ESLint and Prettier extensions, to help you maintain code quality and consistency. Here are some useful extensions:

You can configure your IDE settings according to the Nest JS style guide found in the Nest JS documentation.

Creating Your First Nest JS Application

In this section of the Nest JS tutorial, we will create our first Nest JS application and explore its structure.

Generating a New Project with Nest JS CLI

Open your terminal and run the following command to generate a new Nest JS project:

nest new my-nest-app

Follow the prompts to set up your project. Choose the package manager (npm or yarn) to install the necessary dependencies. Once the setup is complete, navigate to the project directory:

cd my-nest-app

Exploring the Project Structure

Nest JS applications have a modular architecture. Here’s a brief overview of the default project structure:

  • src/: Contains the source code of the application
    • app.controller.ts: Defines the application’s controller
    • app.service.ts: Defines the application’s service
    • app.module.ts: The root module of the application
  • test/: Contains the test files
  • main.ts: The entry point of the application

Each of these files plays a specific role in the application’s architecture:

  • app.module.ts: Registers the application’s components.
  • app.controller.ts: Handles incoming requests and returns responses.
  • app.service.ts: Contains the business logic.

For a detailed explanation of the project structure, refer to the Nest JS documentation.

Running the Application

To run your Nest JS application, use the following command:

npm run start

Open your browser and navigate to http://localhost:3000 to see your application in action. You should see “Hello World!” as the response.

Understanding the Core Concepts of Nest JS

In this part of the Nest JS tutorial, we will dive deeper into the core concepts of Nest JS, which form the backbone of any application built using this framework.

Modules

Modules are the basic building blocks of a Nest JS application. They are used to organize the application into cohesive blocks of functionality. Each application has at least one module, the root module. Here is an example of a simple module:

import { Module } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

For more details on modules, refer to the Nest JS documentation on Modules.

Controllers

Controllers handle incoming requests and return responses to the client. They are decorated with the @Controller() decorator. Here’s a basic example:

import { Controller, Get } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get()
  getHello(): string {
    return this.appService.getHello();
  }
}

Controllers are explained in detail in the Nest JS documentation on Controllers.

Providers

Providers are used for encapsulating business logic. They are decorated with the @Injectable() decorator and are typically used by controllers. Example:

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

@Injectable()
export class AppService {
  getHello(): string {
    return 'Hello World!';
  }
}

Services

Services are a type of provider that contains business logic. They can be injected into controllers and other services to handle complex operations. The example above demonstrates a simple service.

Middleware

Middleware functions are executed before the route handler. They can be used for tasks like logging, authentication, and more. Here is an example of custom middleware:

import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';

@Injectable()
export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    console.log('Request...');
    next();
  }
}

For more details, see the Nest JS documentation on Middleware.

Interceptors

Interceptors are used to add additional logic before or after method execution. They can modify the arguments passed to a method or the result returned by it. Example:

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

@Injectable()
export class TransformInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next.handle().pipe(map(data => ({ data })));
  }
}

Learn more in the Nest JS documentation on Interceptors.

Guards

Guards are used to determine whether a request will be handled by the route handler. They are useful for implementing authorization. Example:

import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
import { Observable } from 'rxjs';

@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(
    context: ExecutionContext,
  ): boolean | Promise<boolean> | Observable<boolean> {
    const request = context.switchToHttp().getRequest();
    return validateRequest(request);
  }
}

Refer to the Nest JS documentation on Guards for more information.

Pipes

Pipes are used for transforming and validating data. They can be used to validate input data and transform it into the desired format. Example:

import { PipeTransform, Injectable, ArgumentMetadata, BadRequestException } from '@nestjs/common';

@Injectable()
export class ParseIntPipe implements PipeTransform<string, number> {
  transform(value: string, metadata: ArgumentMetadata): number {
    const val = parseInt(value, 10);
    if (isNaN(val)) {
      throw new BadRequestException('Validation failed');
    }
    return val;
  }
}

For more details, check the Nest JS documentation on Pipes.

Exception Filters

Exception filters are used to handle exceptions thrown by the application. They can catch exceptions and transform the response accordingly. Example:

import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from '@nestjs/common';
import { Request, Response } from 'express';

@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const request = ctx.getRequest<Request>();
    const status = exception.getStatus();

    response
      .status(status)
      .json({
        statusCode: status,
        timestamp: new Date().toISOString(),
        path: request.url,
      });
  }
}

For more information, see the Nest JS documentation on Exception Filters.

Building a Simple RESTful API with Nest JS

In this section of the Nest JS tutorial, we will build a simple RESTful API using Nest JS. This will involve creating a module, controller, and service, and implementing CRUD (Create, Read, Update, Delete) operations.

Creating a Module, Controller, and Service

Generate a new module, controller, and service using the Nest JS CLI:

nest generate module items
nest generate controller items
nest generate service items

This will create the necessary files for the items module, controller, and service.

Implementing CRUD Operations

Controller: The controller will define routes and handle HTTP requests.

import { Controller, Get, Post, Body, Param, Delete, Put } from '@nestjs/common';
import { ItemsService } from './items.service';
import { CreateItemDto } from './dto/create-item.dto';
import { UpdateItemDto } from './dto/update-item.dto';

@Controller('items')
export class ItemsController {
  constructor(private readonly itemsService: ItemsService) {}

  @Post()
  create(@Body() createItemDto: CreateItemDto) {
    return this.itemsService.create(createItemDto);
  }

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

  @Get(':id')
  findOne(@Param('id') id: string) {
    return this.itemsService.findOne(+id);
  }

  @Put(':id')
  update(@Param('id') id: string, @Body() updateItemDto: UpdateItemDto) {
    return this.itemsService.update(+id, updateItemDto);
  }

  @Delete(':id')
  remove(@Param('id') id: string) {
    return this.itemsService.remove(+id);
  }
}

Service: The service will contain the business logic.

import { Injectable } from '@nestjs/common';
import { CreateItemDto } from './dto/create-item.dto';
import { UpdateItemDto } from './dto/update-item.dto';

@Injectable()
export class ItemsService {
  private readonly items = [];

  create(createItemDto: CreateItemDto) {
    const newItem = { id: Date.now(), ...createItemDto };
    this.items.push(newItem);
    return newItem;
  }

  findAll() {
    return this.items;
  }

  findOne(id: number) {
    return this.items.find(item => item.id === id);
  }

  update(id: number, updateItemDto: UpdateItemDto) {
    const itemIndex = this.items.findIndex(item => item.id === id);
    if (itemIndex > -1) {
      this.items[itemIndex] = { ...this.items[itemIndex], ...updateItemDto };
      return this.items[itemIndex];
    }
    return null;
  }

  remove(id: number) {
    const itemIndex = this.items.findIndex(item => item.id === id);
    if (itemIndex > -1) {
      return this.items.splice(itemIndex, 1);
    }
    return null;
  }
}

Using DTOs (Data Transfer Objects)

DTOs are used to define the structure of the data transferred between the client and the server.

Create DTO:

export class CreateItemDto {
  readonly name: string;
  readonly description: string;
  readonly price: number;
}

Update DTO:

export class UpdateItemDto {
  readonly name?: string;
  readonly description?: string;
  readonly price?: number;
}

For more detailed information on controllers and services, refer to the Nest JS documentation on controllers.

Connecting to a Database

In this part of the Nest JS tutorial, we will connect our application to a PostgreSQL database using TypeORM. We will cover installing and configuring TypeORM, connecting to the database, creating entities and repositories, and performing database migrations.

Installing and Configuring TypeORM

First, install TypeORM and the PostgreSQL driver:

npm install @nestjs/typeorm typeorm pg

Next, configure TypeORM in the app.module.ts file:

import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { ItemsModule } from './items/items.module';

@Module({
  imports: [
    TypeOrmModule.forRoot({
      type: 'postgres',
      host: 'localhost',
      port: 5432,
      username: 'your-username',
      password: 'your-password',
      database: 'your-database',
      entities: [__dirname + '/**/*.entity{.ts,.js}'],
      synchronize: true,
    }),
    ItemsModule,
  ],
})
export class AppModule {}

Refer to the TypeORM documentation for more detailed configuration options.

Connecting to a PostgreSQL Database

Ensure PostgreSQL is installed and running on your machine. Create a database and user for your application. Update the TypeORM configuration with your PostgreSQL credentials.

Creating Entities and Repositories

Entity: Define an entity representing a database table.

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

@Entity()
export class Item {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @Column()
  description: string;

  @Column('decimal')
  price: number;
}

Repository: Inject the repository into the service to perform database operations.

import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { Item } from './item.entity';
import { CreateItemDto } from './dto/create-item.dto';

@Injectable()
export class ItemsService {
  constructor(
    @InjectRepository(Item)
    private itemsRepository: Repository<Item>,
  ) {}

  create(createItemDto: CreateItemDto): Promise<Item> {
    const item = this.itemsRepository.create(createItemDto);
    return this.itemsRepository.save(item);
  }

  findAll(): Promise<Item[]> {
    return this.itemsRepository.find();
  }

  findOne(id: number): Promise<Item> {
    return this.itemsRepository.findOne(id);
  }

  async remove(id: number): Promise<void> {
    await this.itemsRepository.delete(id);
  }
}

Performing Database Migrations

TypeORM provides powerful migration tools to manage database schema changes. Here’s a simple example of how to use migrations:

  1. Create a migration:
npm run typeorm migration:create -n CreateItems
  1. Write migration logic in the generated file.
  2. Run the migration:
npm run typeorm migration:run

For detailed information on migrations, refer to the TypeORM migration documentation.

Using Configuration and Environments

In this section of the Nest JS tutorial, we will manage configuration and environment variables using the ConfigModule.

Managing Configuration with the ConfigModule

Install the @nestjs/config module:

npm install @nestjs/config

Configure it in the app.module.ts file:

import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import { ItemsModule } from './items/items.module';

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
    }),
    ItemsModule,
  ],
})
export class AppModule {}

This makes the configuration globally available. For more details, refer to the ConfigModule documentation.

Setting Up Environment Variables

Create a .env file in the root directory of your project:

DATABASE_HOST=localhost
DATABASE_PORT=5432
DATABASE_USER=myuser
DATABASE_PASSWORD=mypassword
DATABASE_NAME=mydatabase

Access these variables in your service or module:

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

@Injectable()
export class AppService {
  constructor(private configService: ConfigService) {}

  getDatabaseConfig() {
    return {
      host: this.configService.get<string>('DATABASE_HOST'),
      port: this.configService.get<number>('DATABASE_PORT'),
      user: this.configService.get<string>('DATABASE_USER'),
      password: this.configService.get<string>('DATABASE_PASSWORD'),
      name: this.configService.get<string>('DATABASE_NAME'),
    };
  }
}

Using environment variables allows you to manage different configurations for development, testing, and production environments.

Authentication and Authorization

In this part of the Nest JS tutorial, we will implement authentication and authorization using JWT (JSON Web Tokens).

Implementing JWT Authentication

First, install the necessary packages:

npm install @nestjs/jwt @nestjs/passport passport passport-jwt bcrypt

Create an auth module, controller, and service:

nest generate module auth
nest generate controller auth
nest generate service auth

Auth Module: Configure JWT and Passport:

import { Module } from '@nestjs/common';
import { AuthService } from './auth.service';
import { AuthController } from './auth.controller';
import { JwtModule } from '@nestjs/jwt';
import { PassportModule } from '@nestjs/passport';
import { JwtStrategy } from './jwt.strategy';
import { UsersModule } from '../users/users.module';

@Module({
  imports: [
    UsersModule,
    PassportModule,
    JwtModule.register({
      secret: 'SECRET_KEY', // use environment variable in production
      signOptions: { expiresIn: '60m' },
    }),
  ],
  providers: [AuthService, JwtStrategy],
  controllers: [AuthController],
})
export class AuthModule {}

Auth Service: Implement methods for validating users and generating tokens:

import { Injectable } from '@nestjs/common';
import { JwtService } from '@nestjs/jwt';
import { UsersService } from '../users/users.service';
import { User } from '../users/user.entity';

@Injectable()
export class AuthService {
  constructor(
    private usersService: UsersService,
    private jwtService: JwtService
  ) {}

  async validateUser(username: string, pass: string): Promise<any> {
    const user = await this.usersService.findOne(username);
    if (user && user.password === pass) {
      const { password, ...result } = user;
      return result;
    }
    return null;
  }

  async login(user: any) {
    const payload = { username: user.username, sub: user.userId };
    return {
      access_token: this.jwtService.sign(payload),
    };
  }
}

JWT Strategy: Define JWT strategy for protecting routes:

import { Injectable } from '@nestjs/common';
import { PassportStrategy } from '@nestjs/passport';
import { ExtractJwt, Strategy } from 'passport-jwt';

@Injectable()
export class JwtStrategy extends PassportStrategy(Strategy) {
  constructor() {
    super({
      jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
      ignoreExpiration: false,
      secretOrKey: 'SECRET_KEY',
    });
  }

  async validate(payload: any) {
    return { userId: payload.sub, username: payload.username };
  }
}

Auth Controller: Implement endpoints for login:

import { Controller, Request, Post, UseGuards } from '@nestjs/common';
import { AuthService } from './auth.service';
import { LocalAuthGuard } from './local-auth.guard';
import { JwtAuthGuard } from './jwt-auth.guard';

@Controller('auth')
export class AuthController {
  constructor(private authService: AuthService) {}

  @UseGuards(LocalAuthGuard)
  @Post('login')
  async login(@Request() req) {
    return this.authService.login(req.user);
  }

  @UseGuards(JwtAuthGuard)
  @Post('profile')
  getProfile(@Request() req) {
    return req.user;
  }
}

Setting Up User Roles and Permissions

Define user roles and set up guards to protect routes based on roles. Example:

import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
import { Reflector } from '@nestjs/core';

@Injectable()
export class RolesGuard implements CanActivate {
  constructor(private reflector: Reflector) {}

  canActivate(context: ExecutionContext): boolean {
    const roles = this.reflector.get<string[]>('roles', context.getHandler());
    if (!roles) {
      return true;
    }
    const request = context.switchToHttp().getRequest();
    const user = request.user;
    return roles.includes(user.role);
  }
}

Protecting Routes with Guards

Use the RolesGuard to protect specific routes. Example:

import { Controller, Get, UseGuards } from '@nestjs/common';
import { RolesGuard } from './roles.guard';
import { Roles } from './roles.decorator';

@Controller('users')
@UseGuards(RolesGuard)
export class UsersController {
  @Get()
  @Roles('admin')
  findAll() {
    return [];
  }
}

Error Handling and Validation

In this section of the Nest JS tutorial, we will cover error handling and data validation using Pipes and Exception Filters.

Using Pipes for Validation

Pipes in Nest JS are used to transform and validate data. We will use the class-validator and class-transformer packages to handle validation.

First, install the required packages:

npm install class-validator class-transformer

Next, create a DTO (Data Transfer Object) for validation:

import { IsString, IsInt, IsOptional } from 'class-validator';

export class CreateItemDto {
  @IsString()
  name: string;

  @IsString()
  description: string;

  @IsInt()
  price: number;
}

export class UpdateItemDto {
  @IsString()
  @IsOptional()
  name?: string;

  @IsString()
  @IsOptional()
  description?: string;

  @IsInt()
  @IsOptional()
  price?: number;
}

Apply the DTO in the controller:

import { Body, Controller, Post, UsePipes, ValidationPipe } from '@nestjs/common';
import { ItemsService } from './items.service';
import { CreateItemDto } from './dto/create-item.dto';

@Controller('items')
export class ItemsController {
  constructor(private readonly itemsService: ItemsService) {}

  @Post()
  @UsePipes(new ValidationPipe())
  create(@Body() createItemDto: CreateItemDto) {
    return this.itemsService.create(createItemDto);
  }
}

For more information, refer to the Nest JS documentation on Pipes.

Creating Custom Validation Decorators

Custom validation decorators can be used for more complex validation logic. Here’s an example:

import { registerDecorator, ValidationOptions, ValidationArguments } from 'class-validator';

export function IsPositive(validationOptions?: ValidationOptions) {
  return function (object: Object, propertyName: string) {
    registerDecorator({
      name: 'isPositive',
      target: object.constructor,
      propertyName: propertyName,
      options: validationOptions,
      validator: {
        validate(value: any, args: ValidationArguments) {
          return typeof value === 'number' && value > 0;
        },
      },
    });
  };
}

Use the custom decorator in a DTO:

import { IsPositive } from './is-positive.decorator';

export class CreateItemDto {
  @IsPositive({ message: 'Price must be a positive number' })
  price: number;
}

Implementing Exception Filters

Exception filters handle exceptions and transform the response. Here’s an example of a custom exception filter:

import { ExceptionFilter, Catch, ArgumentsHost, HttpException, HttpStatus } from '@nestjs/common';

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const request = ctx.getRequest();

    const status = exception instanceof HttpException
      ? exception.getStatus()
      : HttpStatus.INTERNAL_SERVER_ERROR;

    const message = exception instanceof HttpException
      ? exception.getResponse()
      : { message: 'Internal server error' };

    response.status(status).json({
      statusCode: status,
      message,
      timestamp: new Date().toISOString(),
      path: request.url,
    });
  }
}

Apply the filter in the main file:

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { AllExceptionsFilter } from './common/filters/all-exceptions.filter';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalFilters(new AllExceptionsFilter());
  await app.listen(3000);
}
bootstrap();

For more details, refer to the Nest JS documentation on Exception Filters.

Testing Your Nest JS Application

In this section of the Nest JS tutorial, we will focus on testing our Nest JS application. We’ll cover writing unit tests with Jest, writing end-to-end tests, and mocking dependencies.

Writing Unit Tests with Jest

Jest is the default testing framework used by Nest JS. To start, let’s ensure Jest is installed:

npm install --save-dev jest @types/jest ts-jest

Next, configure Jest in the package.json file:

"jest": {
  "moduleFileExtensions": [
    "js",
    "json",
    "ts"
  ],
  "rootDir": "src",
  "testRegex": ".*\\.spec\\.ts$",
  "transform": {
    "^.+\\.(t|j)s$": "ts-jest"
  },
  "collectCoverageFrom": [
    "**/*.(t|j)s"
  ],
  "coverageDirectory": "../coverage",
  "testEnvironment": "node"
}

Create a sample unit test for the ItemsService:

import { Test, TestingModule } from '@nestjs/testing';
import { ItemsService } from './items.service';

describe('ItemsService', () => {
  let service: ItemsService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [ItemsService],
    }).compile();

    service = module.get<ItemsService>(ItemsService);
  });

  it('should be defined', () => {
    expect(service).toBeDefined();
  });

  it('should create an item', () => {
    const createItemDto = { name: 'Test item', description: 'Test description', price: 10 };
    expect(service.create(createItemDto)).toEqual({
      id: expect.any(Number),
      ...createItemDto,
    });
  });
});

Run the tests using the following command:

npm run test

Refer to the Jest documentation for more details on configuring and using Jest.

Writing End-to-End Tests

End-to-end (E2E) tests ensure that your application works as expected from a user’s perspective. Create an E2E test for the ItemsController:

First, generate the E2E test directory:

mkdir test

Then create a sample E2E test file test/app.e2e-spec.ts:

import { Test, TestingModule } from '@nestjs/testing';
import { INestApplication } from '@nestjs/common';
import * as request from 'supertest';
import { AppModule } from '../src/app.module';

describe('ItemsController (e2e)', () => {
  let app: INestApplication;

  beforeAll(async () => {
    const moduleFixture: TestingModule = await Test.createTestingModule({
      imports: [AppModule],
    }).compile();

    app = moduleFixture.createNestApplication();
    await app.init();
  });

  it('/items (POST)', () => {
    return request(app.getHttpServer())
      .post('/items')
      .send({ name: 'Test item', description: 'Test description', price: 10 })
      .expect(201)
      .expect({
        id: expect.any(Number),
        name: 'Test item',
        description: 'Test description',
        price: 10,
      });
  });

  it('/items (GET)', () => {
    return request(app.getHttpServer())
      .get('/items')
      .expect(200)
      .expect([
        {
          id: expect.any(Number),
          name: 'Test item',
          description: 'Test description',
          price: 10,
        },
      ]);
  });
});

Run E2E tests using the following command:

npm run test:e2e

Mocking Dependencies

Mocking dependencies is essential for isolating the unit of work you are testing. Here’s an example of how to mock the ItemsService in a controller test:

import { Test, TestingModule } from '@nestjs/testing';
import { ItemsController } from './items.controller';
import { ItemsService } from './items.service';

describe('ItemsController', () => {
  let controller: ItemsController;
  let service: ItemsService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      controllers: [ItemsController],
      providers: [
        {
          provide: ItemsService,
          useValue: {
            findAll: jest.fn().mockResolvedValue([{ name: 'Test item' }]),
          },
        },
      ],
    }).compile();

    controller = module.get<ItemsController>(ItemsController);
    service = module.get<ItemsService>(ItemsService);
  });

  it('should return an array of items', async () => {
    expect(await controller.findAll()).toEqual([{ name: 'Test item' }]);
  });
});

For more details on testing and mocking, refer to the Nest JS testing documentation.

Deploying a Nest JS Application

In this section of the Nest JS tutorial, we will cover how to prepare and deploy your Nest JS application for production using Heroku and configure CI/CD pipelines.

Preparing the Application for Production

  1. Environment Variables: Use a .env file to manage environment-specific settings.
  2. Production Build: Modify package.json to include a production build script:
"scripts": {
  "start:prod": "node dist/main"
}

3. Logging and Monitoring: Use middleware to log and monitor application performance..

Deploying to Heroku

  1. Install Heroku CLI: Follow the instructions on the Heroku CLI documentation to install the Heroku CLI.
  2. Login to Heroku: Use the command:
heroku login

3. Create a Heroku Application: Inside your project directory, run:

heroku create

4. Deploy the Application: Push your code to Heroku:

git push heroku main

5. Configure Environment Variables: Set environment variables on Heroku using the CLI or dashboard.

6. Open the Application: After deployment, open your app using:

heroku open

For more details, refer to the Heroku Node.js documentation.

Configuring CI/CD Pipelines

  1. GitHub Actions: Create a GitHub Actions workflow file in .github/workflows/main.yml:
name: CI/CD Pipeline

on:
  push:
    branches:
      - main

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v2
    - name: Set up Node.js
      uses: actions/setup-node@v2
      with:
        node-version: '14'
    - run: npm install
    - run: npm run build
    - run: npm test
    - name: Deploy to Heroku
      env:
        HEROKU_API_KEY: ${{ secrets.HEROKU_API_KEY }}
      run: |
        git remote add heroku https://git.heroku.com/your-heroku-app.git
        git push heroku main

2. Configure Secrets: Add HEROKU_API_KEY to your GitHub repository secrets.

For detailed setup, refer to the GitHub Actions documentation.

Advanced Topics

In this part of the Nest JS tutorial, we will explore some advanced topics to enhance your understanding and capabilities with Nest JS, including WebSockets, GraphQL, and microservices.

WebSockets and Real-Time Communication

WebSockets enable real-time, bidirectional communication between clients and servers. Nest JS provides built-in support for WebSockets.

Installing Dependencies:

npm install @nestjs/websockets @nestjs/platform-socket.io

Creating a WebSocket Gateway:

import { WebSocketGateway, WebSocketServer, SubscribeMessage, MessageBody } from '@nestjs/websockets';
import { Server } from 'socket.io';

@WebSocketGateway()
export class AppGateway {
  @WebSocketServer()
  server: Server;

  @SubscribeMessage('message')
  handleMessage(@MessageBody() message: string): void {
    this.server.emit('message', message);
  }
}

For more details, refer to the Nest JS documentation on WebSockets.

GraphQL Integration

GraphQL is a query language for APIs that provides a more efficient and powerful alternative to REST.

Installing Dependencies:

npm install @nestjs/graphql graphql-tools graphql apollo-server-express

Setting Up GraphQL Module:

import { Module } from '@nestjs/common';
import { GraphQLModule } from '@nestjs/graphql';
import { join } from 'path';

@Module({
  imports: [
    GraphQLModule.forRoot({
      autoSchemaFile: join(process.cwd(), 'src/schema.gql'),
    }),
  ],
})
export class AppModule {}

Creating a Resolver:

import { Resolver, Query, Mutation, Args } from '@nestjs/graphql';
import { ItemsService } from './items.service';
import { CreateItemDto } from './dto/create-item.dto';
import { Item } from './item.entity';

@Resolver(of => Item)
export class ItemsResolver {
  constructor(private itemsService: ItemsService) {}

  @Query(returns => [Item])
  items() {
    return this.itemsService.findAll();
  }

  @Mutation(returns => Item)
  createItem(@Args('createItemDto') createItemDto: CreateItemDto) {
    return this.itemsService.create(createItemDto);
  }
}

For more details, refer to the Nest JS documentation on GraphQL.

Microservices with Nest JS

Microservices architecture allows the development of highly scalable and maintainable applications by breaking down the system into smaller, independent services.

Installing Dependencies:

npm install @nestjs/microservices

Creating a Microservice:

import { NestFactory } from '@nestjs/core';
import { Transport, MicroserviceOptions } from '@nestjs/microservices';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(AppModule, {
    transport: Transport.TCP,
  });
  app.listen(() => console.log('Microservice is listening'));
}
bootstrap();

Defining a Microservice Controller:

import { Controller } from '@nestjs/common';
import { MessagePattern } from '@nestjs/microservices';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @MessagePattern({ cmd: 'sum' })
  accumulate(data: number[]): number {
    return this.appService.accumulate(data);
  }
}

For more details, refer to the Nest JS documentation on Microservices.

Nest JS with Frontend Frameworks

In this section of the Nest JS tutorial, we will discuss how to integrate Nest JS with popular frontend frameworks like Angular, React, and Vue.

Integrating Nest JS with Angular

Angular and Nest JS can be seamlessly integrated due to their shared use of TypeScript.

  1. Set Up Angular Application: Create an Angular application using Angular CLI:
ng new angular-app

2. Nest JS Backend: Ensure your Nest JS application is running.

3. HTTP Client Setup: Use Angular’s HttpClientModule to communicate with the Nest JS backend:

import { HttpClientModule } from '@angular/common/http';

Service to Fetch Data:

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root',
})
export class DataService {
  constructor(private http: HttpClient) {}

  getData() {
    return this.http.get('http://localhost:3000/items');
  }
}

For more detailed steps, refer to the Angular documentation.

Integrating Nest JS with React

React is a popular JavaScript library for building user interfaces.

  1. Set Up React Application: Create a React application using Create React App:
npx create-react-app react-app

2. Nest JS Backend: Ensure your Nest JS application is running.

3. Fetch Data from Nest JS:

import React, { useEffect, useState } from 'react';
import axios from 'axios';

const App = () => {
  const [items, setItems] = useState([]);

  useEffect(() => {
    axios.get('http://localhost:3000/items')
      .then(response => {
        setItems(response.data);
      });
  }, []);

  return (
    <div>
      <h1>Items</h1>
      <ul>
        {items.map(item => (
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
    </div>
  );
};

export default App;

For more detailed steps, refer to the React documentation.

Integrating Nest JS with Vue

Vue.js is a progressive JavaScript framework for building user interfaces.

  1. Set Up Vue Application: Create a Vue application using Vue CLI:
vue create vue-app

2. Nest JS Backend: Ensure your Nest JS application is running.

3. Fetch Data from Nest JS:

<template>
  <div>
    <h1>Items</h1>
    <ul>
      <li v-for="item in items" :key="item.id">{{ item.name }}</li>
    </ul>
  </div>
</template>

<script>
import axios from 'axios';

export default {
  data() {
    return {
      items: [],
    };
  },
  mounted() {
    axios.get('http://localhost:3000/items')
      .then(response => {
        this.items = response.data;
      });
  },
};
</script>

For more detailed steps, refer to the Vue.js documentation.

Performance Optimization

In this section of the Nest JS tutorial, we will discuss various strategies to optimize the performance of your Nest JS applications, including caching, optimizing database queries, and implementing load balancing and scaling.

Caching Strategies

Caching can significantly improve the performance of your application by reducing the load on your database and speeding up response times.

  1. Install Cache Module:
npm install cache-manager

2. Configure Cache Module:

import { Module, CacheModule } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [CacheModule.register()],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

3. Use Cache in Service:

import { Injectable, Cacheable, CacheInterceptor, UseInterceptors } from '@nestjs/common';

@Injectable()
export class ItemsService {
  @UseInterceptors(CacheInterceptor)
  @Cacheable()
  findAll() {
    // Your logic here
  }
}

For more details, refer to the Nest JS documentation on Caching.

Optimizing Database Queries

Efficient database queries can greatly enhance the performance of your application. Here are some tips:

  1. Indexes: Ensure that your database tables have appropriate indexes.
  2. Lazy Loading and Eager Loading: Use these techniques to load only the necessary data.
  3. Query Optimization: Use efficient SQL queries and avoid unnecessary joins.

Example using TypeORM:

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

@Entity()
@Index(['name', 'price'])
export class Item {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @Column('decimal')
  price: number;
}

Refer to the TypeORM documentation for more details on query optimization.

Load Balancing and Scaling

Load balancing and scaling ensure that your application can handle high traffic and provide high availability.

  1. Horizontal Scaling: Add more instances of your application.
  2. Load Balancer: Use a load balancer like NGINX or HAProxy to distribute traffic across multiple instances.

Example NGINX Configuration:

http {
    upstream myapp {
        server 127.0.0.1:3000;
        server 127.0.0.1:3001;
    }

    server {
        listen 80;

        location / {
            proxy_pass http://myapp;
        }
    }
}

For more information on load balancing, refer to the NGINX documentation.

Security Best Practices

In this part of the Nest JS tutorial, we will discuss security best practices to protect your application against common web vulnerabilities.

Protecting Against Common Web Vulnerabilities

  1. SQL Injection: Use parameterized queries and ORM libraries like TypeORM to prevent SQL injection attacks.
  2. Cross-Site Scripting (XSS): Use libraries like DOMPurify to sanitize user inputs and outputs.
  3. Cross-Site Request Forgery (CSRF): Implement CSRF protection mechanisms such as tokens.

Example of XSS Protection:

import * as DOMPurify from 'dompurify';

function sanitize(input: string): string {
  return DOMPurify.sanitize(input);
}

For more details, refer to the OWASP Top Ten.

Implementing HTTPS and Secure Headers

  1. HTTPS: Use HTTPS to encrypt data transmitted between the client and server.
  2. Helmet.js: Use Helmet to set various HTTP headers for security.

Installing Helmet:

npm install helmet

Using Helmet in Nest JS:

import * as helmet from 'helmet';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(helmet());
  await app.listen(3000);
}
bootstrap();

For more details, refer to the Helmet.js documentation.

Using Helmet.js for Security

Helmet helps secure your Express (and Nest JS) apps by setting various HTTP headers.

Example:

import * as helmet from 'helmet';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(helmet());
  await app.listen(3000);
}
bootstrap();

Helmet can protect against vulnerabilities like clickjacking, MIME type sniffing, and more.

File Upload and Management

In this section of the Nest JS tutorial, we will cover handling file uploads using the Multer middleware and managing file storage.

Handling File Uploads with Multer

Multer is a middleware for handling multipart/form-data, which is primarily used for uploading files.

  1. Install Multer:
npm install @nestjs/platform-express multer

2. Configure Multer in a Controller:

import { Controller, Post, UseInterceptors, UploadedFile } from '@nestjs/common';
import { FileInterceptor } from '@nestjs/platform-express';

@Controller('upload')
export class UploadController {
  @Post()
  @UseInterceptors(FileInterceptor('file'))
  uploadFile(@UploadedFile() file: Express.Multer.File) {
    console.log(file);
  }
}

3. Configure Multer Options (optional):

import { MulterModule } from '@nestjs/platform-express';
import { diskStorage } from 'multer';
import { Module } from '@nestjs/common';

@Module({
  imports: [
    MulterModule.register({
      storage: diskStorage({
        destination: './uploads',
        filename: (req, file, cb) => {
          const filename = `${Date.now()}-${file.originalname}`;
          cb(null, filename);
        },
      }),
    }),
  ],
  controllers: [UploadController],
})
export class UploadModule {}

For more details, refer to the Multer documentation and the Nest JS documentation on file upload.

Storing and Retrieving Files

To store and retrieve files, we can use a dedicated service.

  1. Create a File Service:
import { Injectable } from '@nestjs/common';
import { writeFile, readFile } from 'fs/promises';
import { join } from 'path';

@Injectable()
export class FileService {
  async saveFile(file: Express.Multer.File): Promise<string> {
    const filePath = join(__dirname, '..', 'uploads', file.originalname);
    await writeFile(filePath, file.buffer);
    return filePath;
  }

  async getFile(filename: string): Promise<Buffer> {
    const filePath = join(__dirname, '..', 'uploads', filename);
    return readFile(filePath);
  }
}

2. Use the File Service in a Controller:

import { Controller, Get, Param, Post, UploadedFile, UseInterceptors } from '@nestjs/common';
import { FileInterceptor } from '@nestjs/platform-express';
import { FileService } from './file.service';

@Controller('files')
export class FileController {
  constructor(private readonly fileService: FileService) {}

  @Post('upload')
  @UseInterceptors(FileInterceptor('file'))
  async uploadFile(@UploadedFile() file: Express.Multer.File) {
    const filePath = await this.fileService.saveFile(file);
    return { filePath };
  }

  @Get(':filename')
  async getFile(@Param('filename') filename: string) {
    const file = await this.fileService.getFile(filename);
    return file;
  }
}

Internationalization (i18n)

In this section of the Nest JS tutorial, we will discuss how to set up internationalization (i18n) to manage multiple languages and locales in your Nest JS application.

Setting Up Internationalization in Nest JS

  1. Install the Required Packages:
npm install @nestjs/i18n i18n

2. Configure the i18n Module:

import { Module } from '@nestjs/common';
import { I18nModule, I18nJsonParser } from 'nestjs-i18n';
import { join } from 'path';
import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [
    I18nModule.forRoot({
      fallbackLanguage: 'en',
      parser: I18nJsonParser,
      parserOptions: {
        path: join(__dirname, '/i18n/'),
        watch: true,
      },
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

3. Create Translation Files:

  • Create a directory named i18n in the src folder.
  • Add JSON files for each language, e.g., en.json, fr.json:
// en.json
{
  "HELLO": "Hello",
  "WELCOME": "Welcome to our application"
}

// fr.json
{
  "HELLO": "Bonjour",
  "WELCOME": "Bienvenue dans notre application"
}

4. Use i18n Service in Controllers:

import { Controller, Get } from '@nestjs/common';
import { I18nService } from 'nestjs-i18n';

@Controller()
export class AppController {
  constructor(private readonly i18n: I18nService) {}

  @Get('hello')
  async getHello(): Promise<string> {
    return this.i18n.translate('HELLO');
  }
}

Managing Translations and Locales

  1. Dynamic Translation: Use the I18nService to dynamically translate content based on the current locale.
  2. Locale Middleware: Implement middleware to set the locale based on user preferences or request headers.

Example Middleware:

import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';
import { I18nService } from 'nestjs-i18n';

@Injectable()
export class LocaleMiddleware implements NestMiddleware {
  constructor(private readonly i18n: I18nService) {}

  use(req: Request, res: Response, next: NextFunction) {
    const locale = req.headers['accept-language'] || 'en';
    this.i18n.setLocale(locale);
    next();
  }
}

Register Middleware:

import { Module, NestModule, MiddlewareConsumer } from '@nestjs/common';
import { LocaleMiddleware } from './locale.middleware';

@Module({
  // ...
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(LocaleMiddleware).forRoutes('*');
  }
}

For more information on internationalization, refer to the Nest JS i18n documentation.

API Documentation with Swagger

In this section of the Nest JS tutorial, we will discuss how to set up Swagger to generate API documentation for your Nest JS application.

Setting Up Swagger in a Nest JS Application

  1. Install Swagger Dependencies:
npm install @nestjs/swagger swagger-ui-express

2. Configure Swagger in the Main File:

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);

  const config = new DocumentBuilder()
    .setTitle('Nest JS Tutorial')
    .setDescription('The API description')
    .setVersion('1.0')
    .addTag('items')
    .build();
  const document = SwaggerModule.createDocument(app, config);
  SwaggerModule.setup('api', app, document);

  await app.listen(3000);
}
bootstrap();

3. Decorate Your Endpoints:

Use Swagger decorators to document your endpoints.

import { Controller, Get, Post, Body } from '@nestjs/common';
import { ApiTags, ApiOperation, ApiResponse, ApiBody } from '@nestjs/swagger';
import { CreateItemDto } from './dto/create-item.dto';
import { Item } from './item.entity';
import { ItemsService } from './items.service';

@ApiTags('items')
@Controller('items')
export class ItemsController {
  constructor(private readonly itemsService: ItemsService) {}

  @Post()
  @ApiOperation({ summary: 'Create item' })
  @ApiResponse({ status: 201, description: 'The item has been created.', type: Item })
  @ApiBody({ type: CreateItemDto })
  create(@Body() createItemDto: CreateItemDto) {
    return this.itemsService.create(createItemDto);
  }

  @Get()
  @ApiOperation({ summary: 'Get all items' })
  @ApiResponse({ status: 200, description: 'Returns all items.', type: [Item] })
  findAll() {
    return this.itemsService.findAll();
  }
}

4. Access Swagger Documentation:Start your application and navigate to http://localhost:3000/api to access the Swagger UI with your API documentation.

For more details, refer to the Nest JS documentation on Swagger.

Task Scheduling

In this section of the Nest JS tutorial, we will discuss how to use the Schedule module to manage and execute cron jobs.

Using the Schedule Module

  1. Install the Schedule Module:
npm install @nestjs/schedule
npm install --save-dev @types/cron

2. Import and Configure the Schedule Module:

import { Module } from '@nestjs/common';
import { ScheduleModule } from '@nestjs/schedule';
import { AppService } from './app.service';
import { AppController } from './app.controller';

@Module({
  imports: [ScheduleModule.forRoot()],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

3. Create a Scheduled Task:

import { Injectable } from '@nestjs/common';
import { Cron, CronExpression, Interval, Timeout } from '@nestjs/schedule';

@Injectable()
export class AppService {
  @Cron(CronExpression.EVERY_MINUTE)
  handleCron() {
    console.log('Called every minute');
  }

  @Interval(10000)
  handleInterval() {
    console.log('Called every 10 seconds');
  }

  @Timeout(5000)
  handleTimeout() {
    console.log('Called once after 5 seconds');
  }
}

Managing and Executing Cron Jobs

  1. Cron Jobs: Define cron jobs using the @Cron() decorator and specify a cron expression for scheduling.
@Cron(CronExpression.EVERY_DAY_AT_MIDNIGHT)
handleDailyJob() {
  console.log('Called at midnight every day');
}

2. Intervals: Use the @Interval() decorator to schedule tasks at regular intervals.

@Interval(60000)
handleIntervalJob() {
  console.log('Called every 60 seconds');
}

3. Timeouts: Use the @Timeout() decorator to schedule a one-time task after a delay.

@Timeout(10000)
handleTimeoutJob() {
  console.log('Called once after 10 seconds');
}

For more details, refer to the Nest JS documentation on Task Scheduling.

Caching

In this section of the Nest JS tutorial, we will explore how to implement caching in your Nest JS application using Redis and the CacheModule.

Implementing Caching with Redis

  1. Install Redis and Cache Dependencies:
npm install cache-manager cache-manager-redis-store

2. Configure CacheModule:

import { Module, CacheModule } from '@nestjs/common';
import * as redisStore from 'cache-manager-redis-store';

@Module({
  imports: [
    CacheModule.register({
      store: redisStore,
      host: 'localhost',
      port: 6379,
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

Using the Cache in a Service

  1. Inject CacheManager:
import { Injectable, Cacheable, Inject } from '@nestjs/common';
import { CACHE_MANAGER } from '@nestjs/common';
import { Cache } from 'cache-manager';

@Injectable()
export class ItemsService {
  constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

  async getItems(): Promise<any> {
    const cachedItems = await this.cacheManager.get('items');
    if (cachedItems) {
      return cachedItems;
    }
    const items = await this.fetchItemsFromDb(); // Replace with actual DB fetch
    await this.cacheManager.set('items', items, { ttl: 1000 });
    return items;
  }
}

2. Cache Interceptor:

import { CacheInterceptor, Controller, Get, UseInterceptors } from '@nestjs/common';

@Controller('items')
@UseInterceptors(CacheInterceptor)
export class ItemsController {
  @Get()
  findAll() {
    // Your service call to get items
  }
}

Strategies for Cache Management

  1. Time-to-Live (TTL): Set TTL to control the duration for which the data should be cached.
  2. Cache Invalidation: Implement strategies to invalidate or refresh the cache when the underlying data changes.
  3. Cache Keys: Use descriptive and structured keys for easier cache management.

For more details, refer to the Nest JS documentation on caching.

Logging

In this section of the Nest JS tutorial, we will discuss setting up a logging system to monitor and debug your Nest JS applications.

Setting Up a Logging System

Nest JS provides a built-in Logger service that you can use for logging messages.

  1. Basic Usage:
import { Logger } from '@nestjs/common';

export class AppService {
  private readonly logger = new Logger(AppService.name);

  findAll() {
    this.logger.log('Fetching all items');  // Info level log
    // Your code here
  }
}

Using Built-In Logging Mechanisms

  1. Log Levels: Nest JS supports different log levels: log, error, warn, debug, and verbose.
this.logger.error('Error message');
this.logger.warn('Warning message');
this.logger.debug('Debug message');
this.logger.verbose('Verbose message');

2. Custom Logger: You can create a custom logger by extending the built-in Logger class.

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

export class CustomLogger extends Logger {
  log(message: string) {
    // Custom implementation
    super.log(message);
  }
}

Use your custom logger:

const customLogger = new CustomLogger();
customLogger.log('Custom log message');

For more information, refer to the Nest JS documentation on logging.

Integrating Third-Party Logging Services

  1. Winston: A popular logging library for Node.js.Install Winston:
npm install winston @nestjs/winston

Configure Winston in Nest JS:

import { WinstonModule } from 'nest-winston';
import * as winston from 'winston';

@Module({
  imports: [
    WinstonModule.forRoot({
      transports: [
        new winston.transports.Console(),
        new winston.transports.File({ filename: 'combined.log' }),
      ],
    }),
  ],
})
export class AppModule {}

Use Winston for logging:

import { Inject } from '@nestjs/common';
import { WINSTON_MODULE_PROVIDER } from 'nest-winston';
import { Logger } from 'winston';

export class AppService {
  constructor(
    @Inject(WINSTON_MODULE_PROVIDER) private readonly logger: Logger,
  ) {}

  findAll() {
    this.logger.info('Fetching all items');
  }
}

For more details on using Winston, refer to the Winston documentation.

Health Checks

In this section of the Nest JS tutorial, we will discuss how to implement health checks to monitor the health of your Nest JS application using the Terminus module.

Implementing Health Checks

  1. Install Terminus:
npm install @nestjs/terminus

2. Configure Terminus Module:

import { Module } from '@nestjs/common';
import { TerminusModule } from '@nestjs/terminus';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { TypeOrmHealthIndicator } from '@nestjs/terminus';

@Module({
  imports: [TerminusModule],
  controllers: [AppController],
  providers: [AppService, TypeOrmHealthIndicator],
})
export class AppModule {}

3. Create Health Controller:

import { Controller, Get } from '@nestjs/common';
import { HealthCheck, HealthCheckService, TypeOrmHealthIndicator } from '@nestjs/terminus';

@Controller('health')
export class HealthController {
  constructor(
    private health: HealthCheckService,
    private db: TypeOrmHealthIndicator,
  ) {}

  @Get()
  @HealthCheck()
  check() {
    return this.health.check([
      () => this.db.pingCheck('database'),
    ]);
  }
}

Monitoring Application Health

  1. Health Endpoint: Create a /health endpoint to monitor the health of your application.
@Controller('health')
export class HealthController {
  constructor(private health: HealthCheckService) {}

  @Get()
  @HealthCheck()
  check() {
    return this.health.check([]);
  }
}

2. Custom Health Indicators: Implement custom health indicators to monitor specific parts of your application.

import { Injectable } from '@nestjs/common';
import { HealthIndicator, HealthIndicatorResult, HealthCheckError } from '@nestjs/terminus';

@Injectable()
export class CustomHealthIndicator extends HealthIndicator {
  async isHealthy(key: string): Promise<HealthIndicatorResult> {
    const isHealthy = true; // Your health check logic
    const result = this.getStatus(key, isHealthy);
    if (isHealthy) {
      return result;
    }
    throw new HealthCheckError('Health check failed', result);
  }
}

For more details, refer to the Nest JS documentation on Health Checks.

Real-World Projects and Examples

In this section of the Nest JS tutorial, we will cover building real-world applications using Nest JS. We’ll build a simple blog application, an e-commerce backend, and a social media API.

Building a Simple Blog Application

  1. Set Up the Project: Generate a new Nest JS project.
nest new blog-app

2. Create Blog Module, Controller, and Service:

nest generate module blog
nest generate controller blog
nest generate service blog

3. Define Blog Entity:

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

@Entity()
export class Blog {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  title: string;

  @Column()
  content: string;

  @Column({ default: true })
  isPublished: boolean;
}

4. Implement CRUD Operations in Blog Service:

import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { Blog } from './blog.entity';

@Injectable()
export class BlogService {
  constructor(
    @InjectRepository(Blog)
    private blogRepository: Repository<Blog>,
  ) {}

  create(blog: Blog) {
    return this.blogRepository.save(blog);
  }

  findAll(): Promise<Blog[]> {
    return this.blogRepository.find();
  }

  findOne(id: number): Promise<Blog> {
    return this.blogRepository.findOne(id);
  }

  update(id: number, blog: Partial<Blog>) {
    return this.blogRepository.update(id, blog);
  }

  remove(id: number) {
    return this.blogRepository.delete(id);
  }
}

5. Create Blog Controller:

import { Controller, Get, Post, Body, Param, Delete, Put } from '@nestjs/common';
import { BlogService } from './blog.service';
import { Blog } from './blog.entity';

@Controller('blogs')
export class BlogController {
  constructor(private readonly blogService: BlogService) {}

  @Post()
  create(@Body() blog: Blog) {
    return this.blogService.create(blog);
  }

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

  @Get(':id')
  findOne(@Param('id') id: number) {
    return this.blogService.findOne(id);
  }

  @Put(':id')
  update(@Param('id') id: number, @Body() blog: Partial<Blog>) {
    return this.blogService.update(id, blog);
  }

  @Delete(':id')
  remove(@Param('id') id: number) {
    return this.blogService.remove(id);
  }
}

Creating an E-Commerce Backend

  1. Set Up the Project:
nest new ecommerce-backend

2. Create Product Module, Controller, and Service:

nest generate module products
nest generate controller products
nest generate service products

3. Define Product Entity:

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

@Entity()
export class Product {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @Column()
  description: string;

  @Column('decimal')
  price: number;

  @Column()
  stock: number;
}

4. Implement Product Service and Controller: Follow similar steps as the blog application to implement CRUD operations for the products.

Developing a Social Media API

  1. Set Up the Project:
nest new social-media-api

2. Create User and Post Modules, Controllers, and Services:

nest generate module users
nest generate controller users
nest generate service users
nest generate module posts
nest generate controller posts
nest generate service posts

3. Define User and Post Entities:

// user.entity.ts
import { Entity, Column, PrimaryGeneratedColumn, OneToMany } from 'typeorm';
import { Post } from '../posts/post.entity';

@Entity()
export class User {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  username: string;

  @Column()
  email: string;

  @OneToMany(() => Post, post => post.user)
  posts: Post[];
}

// post.entity.ts
import { Entity, Column, PrimaryGeneratedColumn, ManyToOne } from 'typeorm';
import { User } from '../users/user.entity';

@Entity()
export class Post {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  content: string;

  @ManyToOne(() => User, user => user.posts)
  user: User;
}

4. Implement User and Post Services and Controllers: Follow similar steps as the previous applications to implement CRUD operations and manage user-post relationships.

Conclusion

In this final section of the Nest JS tutorial, we will recap the key points covered throughout the tutorial and encourage further exploration of more advanced features and topics.

Recap of Key Points

  1. Introduction: We introduced Nest JS, its benefits, and the overall structure of the tutorial.
  2. Setting Up Your Development Environment: We covered the prerequisites, installing Node.js, npm, and the Nest JS CLI, and configuring your IDE.
  3. Creating Your First Nest JS Application: We generated a new project, explored its structure, and ran the application.
  4. Understanding the Core Concepts of Nest JS: We delved into modules, controllers, providers, services, middleware, interceptors, guards, pipes, and exception filters.
  5. Building a Simple RESTful API with Nest JS: We created a module, controller, and service, and implemented CRUD operations using DTOs.
  6. Connecting to a Database: We installed and configured TypeORM, connected to a PostgreSQL database, created entities and repositories, and performed database migrations.
  7. Using Configuration and Environments: We managed configuration with the ConfigModule and set up environment variables.
  8. Authentication and Authorization: We implemented JWT authentication, set up user roles and permissions, and protected routes with guards.
  9. Error Handling and Validation: We used pipes for validation, created custom validation decorators, and implemented exception filters.
  10. Testing Your Nest JS Application: We wrote unit tests with Jest, wrote end-to-end tests, and mocked dependencies.
  11. Deploying a Nest JS Application: We prepared the application for production, deployed to Heroku, and configured CI/CD pipelines.
  12. Advanced Topics: We explored WebSockets, GraphQL integration, and microservices with Nest JS.
  13. Nest JS with Frontend Frameworks: We integrated Nest JS with Angular, React, and Vue.
  14. Performance Optimization: We discussed caching strategies, optimizing database queries, and implementing load balancing and scaling.
  15. Security Best Practices: We protected against common web vulnerabilities, implemented HTTPS and secure headers, and used Helmet.js for security.
  16. File Upload and Management: We handled file uploads with Multer and managed file storage.
  17. Internationalization (i18n): We set up internationalization in Nest JS and managed translations and locales.
  18. API Documentation with Swagger: We set up Swagger to generate API documentation.
  19. Task Scheduling: We used the Schedule module to manage and execute cron jobs.
  20. Caching: We implemented caching with Redis and discussed cache management strategies.
  21. Logging: We set up a logging system, used built-in logging mechanisms, and integrated third-party logging services.
  22. Health Checks: We implemented health checks using the Terminus module to monitor application health.
  23. Real-World Projects and Examples: We built a simple blog application, an e-commerce backend, and a social media API.

Encouragement to Explore More Advanced Features

Nest JS offers many more advanced features and techniques that can further enhance your application. Some areas to explore include:

  • Advanced Microservices Patterns: Learn about patterns like Saga and CQRS.
  • Serverless Architecture: Deploy Nest JS applications on serverless platforms like AWS Lambda.
  • GraphQL Subscriptions: Implement real-time updates with GraphQL subscriptions.
  • Advanced Security Techniques: Implement OAuth, OpenID Connect, and other advanced security protocols.
  • Performance Monitoring: Use tools like Prometheus and Grafana for monitoring application performance.

The Nest JS documentation is a comprehensive resource that provides detailed information on these and many other advanced topics.

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