ValidationPipe in depth in NestJS - Mini Project: Build & Apply

ValidationPipe in depth

📖 Scenario: You are building a simple NestJS API to accept user registration data. You want to ensure the data is valid before processing it.

🎯 Goal: Build a NestJS controller that uses ValidationPipe to validate incoming user data with DTOs and class-validator decorators.

📋 What You'll Learn

Create a User DTO class with validation decorators

Set up a ValidationPipe instance with whitelist enabled

Use ValidationPipe in the controller to validate incoming data

Return the validated user data from the controller method

💡 Why This Matters

🌍 Real World

Validating user input in APIs is essential to prevent bad data and security issues. ValidationPipe helps automate this in NestJS.

💼 Career

Backend developers often use validation pipes to ensure data integrity and improve API reliability.

1

Create User DTO with validation decorators

Create a class called CreateUserDto with three properties: username (string, minimum length 3), email (string, must be an email), and age (number, minimum 18). Use class-validator decorators @IsString(), @MinLength(3), @IsEmail(), and @Min(18) as appropriate.

NestJS

import { IsString, MinLength, IsEmail, Min } from 'class-validator';

// Your code here

Need a hint?

Use class-validator decorators on each property to enforce the rules.

2

Configure ValidationPipe with whitelist

Create a constant called validationPipe that is a new instance of ValidationPipe with the option whitelist: true.

NestJS

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

import { IsString, MinLength, IsEmail, Min } from 'class-validator';

export class CreateUserDto {
  @IsString()
  @MinLength(3)
  username: string;

  @IsEmail()
  email: string;

  @Min(18)
  age: number;
}

// Your code here

Need a hint?

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

3

Use ValidationPipe in controller method

Create a NestJS controller class called UserController with a method createUser that accepts a body parameter of type CreateUserDto. Use the @Body() decorator with the validationPipe to validate the input. The method should return the validated body.

NestJS

import { Controller, Post, Body } from '@nestjs/common';

import { CreateUserDto, validationPipe } from './dto';

// Your code here

Need a hint?

Use @Body(validationPipe) to apply validation on the input DTO.

4

Complete module setup with controller

Create a NestJS module class called UserModule that imports Module from '@nestjs/common' and declares the UserController in its controllers array.

NestJS

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

// Your code here

Need a hint?

Use @Module({ controllers: [UserController] }) to declare the controller.