NestJs Complete Guide – Blog by Bidur Sapkota

Table of Content

Nest from Scratch
With Nest CLI
Validating data with ValidationPipe

Nest from Scratch

Initialize project and install dependencies

npm init -y
npm install @nestjs/[email protected] @nestjs/[email protected] @nestjs/[email protected] [email protected] [email protected]

Library	Description
@nestjs/common	Contains vast majority of functions, classes, etc, that we need from Nest
@nestjs/core	The core runtime of NestJS that powers dependency injection, module loading, and lifecycle management
@nestjs/platform-express	Lets Nest use Express JS for handling HTTP requests
reflect-metadata	Helps make decorators work. Tons more on this in just a minute!
typescript	We write Nest apps with Typescript.

Initialize typescript - (tsconfig.json)

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "es2017",
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

Setting	Description
"experimentalDecorators": true	Enables the use of decorators (@Something) in TypeScript. Without this, NestJS decorators (like @Controller()) would throw errors.
"emitDecoratorMetadata": true	Works together with the reflect-metadata library. Emits extra type information about classes and methods at runtime, which NestJS uses for dependency injection.

Common pattern in server

flowchart LR
    A[Request]
    G[Response]
    subgraph Server
        direction LR
        B[**Pipe**<br/><br/>Validate data<br/>contained in<br/>the request]
        B --> C[**Guard**<br/><br/>Make sure<br/>the user is<br/>authenticated]
        C --> D[**Controller**<br/><br/>Route the<br/>request to a<br/>particular<br/>function]
        D --> E[**Service**<br/><br/>Run some<br/>business logic]
        E --> F[**Repository**<br/><br/>Access a<br/>database]
    end

    A --> Server
    direction RL
    Server --> G

    %% Define style classes
    classDef bigText font-size:30px;

    %% Apply them
    class A,B,C,D,E,F,G bigText

NestJS provides More

Part	Description
Pipes	Validates incoming data
Guards	Handles authentication
Controllers	Handles incoming requests
Services	Handles data access and business logic
Repositories	Handles data stored in a DB
Modules	Groups together code
Filters	Handles errors that occur during request handling
Interceptors	Adds extra logic to incoming requests or outgoing responses

We need at least module and controller

Create (`src/main.ts`)

import { Controller, Module, Get } from "@nestjs/common";
import { NestFactory } from "@nestjs/core";

@Controller()
class AppController {
  @Get()
  getRootRoute() {
    return "hi there!";
  }
}

@Module({
  controllers: [AppController],
})
class AppModule {}

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

bootstrap();

Run

npx ts-node-dev src\main.ts

Should give Nest application successfully started

Check at `localhost:3000`

Refactoring

File Structure

main.ts
- function bootstrap
app.controller.ts
- class AppController {}
app.module.ts
- class AppModule {}

Conventions

One class per file (some exceptions)
Class names should include the kind of thing we are creating
Name of class and name of file should always match up
Filename template: name.type_of_thing.ts

Create `app.controller.ts`

import { Controller, Get } from "@nestjs/common";

@Controller()
export class AppController {
  @Get()
  getRootRoute() {
    return "hi there!";
  }
}

Create `app.module.ts`

import { Module } from "@nestjs/common";
import { AppController } from "./app.controller";

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

Update `app.controller.ts`

import { NestFactory } from "@nestjs/core";
import { AppModule } from "./app.module";

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

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

Adding more Routes

Update `app.controller.ts`

import { Controller, Get } from "@nestjs/common";

@Controller("/app")
export class AppController {
  @Get("/hi")
  getRootRoute() {
    return "hi there!";
  }

  @Get("/bye")
  getByeThere() {
    return "bye there!";
  }
}

With Nest CLI

Install nest cli

npm i -g @nestjs/cli

Create nest project (message)

nest new project_name

Run the project

npm run start:dev

Delete everything in src folder except main

Generate messages module

nest generate module messages

Use message module in main (Remove app module)

import { NestFactory } from "@nestjs/core";
import { MessagesModule } from "./messages/messages.module";

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

Generate Controller inside messages folder

nest generate controller messages/messages --flat

--flat says dont create folder called controllers

Update src/messages/messages.controller.ts

import { Controller, Get, Post } from "@nestjs/common";

@Controller("messages")
export class MessagesController {
  @Get()
  listMessages() {}

  @Post()
  createMessage() {}

  @Get("/:id")
  getMessage() {}
}

Test using Postman or Thunder Client (vscode extension) for success status code

Access Body and Params

Update src/messages/messages.controller.ts

import { Controller, Get, Post, Body, Param } from "@nestjs/common";

@Controller("messages")
export class MessagesController {
  @Get()
  listMessages() {}

  @Post()
  createMessage(@Body() body: any) {
    console.log(body);
  }

  @Get("/:id")
  getMessage(@Param("id") id: string) {
    console.log(id);
  }
}

Test for console log

Validating data with ValidationPipe

Install required packages for validation

npm install class-validator class-transformer

Update src/main.ts
- import ValidationPipe
- use validation pipe globally in all routes
- validation will run for only those routes with validation rules

import { NestFactory } from '@nestjs/core';
+ import { ValidationPipe } from '@nestjs/common';
import { MessagesModule } from './messages/messages.module';

async function bootstrap() {
   const app = await NestFactory.create(MessagesModule);
+  app.useGlobalPipes(new ValidationPipe());
   await app.listen(3000);
}
bootstrap();

Create class describing properties of request body

also called Data Transfer Object (DTO)
create src/messages/dtos/create-message.dto.ts

export class CreateMessageDto {
  content: string;
}

Add validation rules

applied whenever instance of this dto is created
update src/messages/dtos/create-message.dto.ts

+ import { IsString } from 'class-validator';

export class CreateMessageDto {
+  @IsString()
   content: string;
}

Apply Validation in Controller route handler

How just adding dto type works?

When ts compiles to js. Type information is lost but Because of emitDecoratorMetadata in tsconfig, some of type information is also converted into javascript

Update src/messages/messages.controller.ts

import { Controller, Get, Post, Body, Param } from '@nestjs/common';
+ import { CreateMessageDto } from './dtos/create-message.dto';

@Controller('messages')
export class MessagesController {
  @Get()
  listMessages() {}

  @Post()
+  createMessage(@Body() body: CreateMessageDto) {
    console.log(body);
  }

  @Get('/:id')
  getMessage(@Param('id') id: string) {
    console.log(id);
  }
}

What is happening

class-transformer converts json body into instance of dto class
class-validator is used to validate the dto instance
if validation error occurs, respond with error 400

NestJS Course

Table of Content

Nest from Scratch

Initialize project and install dependencies

Initialize typescript - (tsconfig.json)

Common pattern in server

NestJS provides More

We need at least module and controller

Create (src/main.ts)

Run

Check at localhost:3000

Refactoring

File Structure

Conventions

Create app.controller.ts

Create app.module.ts

Update app.controller.ts

Adding more Routes

Update app.controller.ts

With Nest CLI

Install nest cli

Create nest project (message)

Run the project

Delete everything in src folder except main

Generate messages module

Use message module in main (Remove app module)

Generate Controller inside messages folder

Update src/messages/messages.controller.ts

Access Body and Params

Validating data with ValidationPipe

Create class describing properties of request body

Add validation rules

Apply Validation in Controller route handler

What is happening

Create (`src/main.ts`)

Check at `localhost:3000`

Create `app.controller.ts`

Create `app.module.ts`

Update `app.controller.ts`

Update `app.controller.ts`