ValidationPipe setup in NestJS - Mini Project: Build & Apply

ValidationPipe setup

📖 Scenario: You are building a simple NestJS API that accepts user data. To keep your API safe and clean, you want to add validation to the incoming data.

🎯 Goal: Set up a ValidationPipe in your NestJS application to automatically validate incoming requests based on DTO rules.

📋 What You'll Learn

Create a DTO class with validation decorators

Create a ValidationPipe instance with whitelist enabled

Apply the ValidationPipe globally in the main application bootstrap

Ensure the application uses the DTO and validation pipe correctly

💡 Why This Matters

🌍 Real World

ValidationPipe helps keep APIs safe by checking incoming data automatically, preventing bad or unexpected data from causing errors or security issues.

💼 Career

Backend developers often use ValidationPipe in NestJS to enforce data rules and improve API reliability and security.

1

Create a User DTO with validation decorators

Create a class called CreateUserDto with two properties: username and age. Use @IsString() decorator on username and @IsInt() decorator on age from the class-validator package.

NestJS

# Create the CreateUserDto class with username and age properties
# Use @IsString() on username and @IsInt() on age
# Your code here

Need a hint?

Remember to import IsString and IsInt from class-validator.

2

Create a ValidationPipe instance with whitelist enabled

Create a constant called validationPipe and assign it a new ValidationPipe instance with the option whitelist: true.

NestJS

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

// Create validationPipe with whitelist enabled
# Your code here

Need a hint?

Use new ValidationPipe({ whitelist: true }) to create the pipe.

3

Apply the ValidationPipe globally in the main bootstrap function

In the bootstrap function, after creating the app with NestFactory.create(AppModule), apply the validationPipe globally using app.useGlobalPipes(validationPipe).

NestJS

import { IsString, IsInt } from 'class-validator';
import { ValidationPipe } from '@nestjs/common';
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

export class CreateUserDto {
  @IsString()
  username: string;

  @IsInt()
  age: number;
}

const validationPipe = new ValidationPipe({ whitelist: true });

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  
  // Apply validationPipe globally
  # Your code here

  await app.listen(3000);
}

bootstrap();

Need a hint?

Use app.useGlobalPipes(validationPipe) to apply the pipe globally.

4

Use the CreateUserDto in a controller method

In a controller method, add a parameter called createUserDto of type CreateUserDto decorated with @Body() to receive and validate incoming user data.

NestJS

import { IsString, IsInt } from 'class-validator';
import { ValidationPipe } from '@nestjs/common';
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { Controller, Post, Body } from '@nestjs/common';

export class CreateUserDto {
  @IsString()
  username: string;

  @IsInt()
  age: number;
}

const validationPipe = new ValidationPipe({ whitelist: true });

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

bootstrap();

@Controller('users')
export class UsersController {
  @Post()
  create(
    // Add a parameter called createUserDto of type CreateUserDto decorated with @Body()
    # Your code here
  ) {
    return 'User created';
  }
}

Need a hint?

Use @Body() createUserDto: CreateUserDto as the method parameter.