class-validator decorators in NestJS - Mini Project: Build & Apply

Validating User Input with class-validator Decorators in NestJS

📖 Scenario: You are building a simple user registration form in a NestJS backend. You want to ensure that the data sent by users is valid before processing it.

🎯 Goal: Create a User Data Transfer Object (DTO) class using class-validator decorators to validate user input fields like username, email, and age.

📋 What You'll Learn

Create a class called UserDto with properties username, email, and age.

Add validation decorators @IsString() and @Length(3, 20) to username.

Add validation decorators @IsEmail() to email.

Add validation decorators @IsInt(), @Min(18), and @Max(99) to age.

💡 Why This Matters

🌍 Real World

Validating user input is essential in web applications to prevent bad data and security issues. Using class-validator decorators in NestJS makes this easy and clean.

💼 Career

Backend developers working with NestJS often create DTOs with validation decorators to ensure data integrity and improve application reliability.

1

Create the UserDto class with properties

Create a class called UserDto with three properties: username of type string, email of type string, and age of type number.

NestJS

export class UserDto {
  // Define username, email, and age properties here
}

Need a hint?

Define a class with three properties and their types exactly as specified.

2

Add validation decorators for username

Import IsString and Length from class-validator. Add the decorators @IsString() and @Length(3, 20) above the username property.

NestJS

import { IsString, Length } from 'class-validator';

export class UserDto {
  // Add @IsString() and @Length(3, 20) decorators to username
  username: string;
  email: string;
  age: number;
}

Need a hint?

Remember to import the decorators before using them.

3

Add validation decorator for email

Import IsEmail from class-validator. Add the decorator @IsEmail() above the email property.

NestJS

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

export class UserDto {
  @IsString()
  @Length(3, 20)
  username: string;
  // Add @IsEmail() decorator to email
  email: string;
  age: number;
}

Need a hint?

Use @IsEmail() to check if the email is valid.

4

Add validation decorators for age

Import IsInt, Min, and Max from class-validator. Add the decorators @IsInt(), @Min(18), and @Max(99) above the age property.

NestJS

import { IsString, Length, IsEmail, IsInt, Min, Max } from 'class-validator';

export class UserDto {
  @IsString()
  @Length(3, 20)
  username: string;

  @IsEmail()
  email: string;

  // Add @IsInt(), @Min(18), and @Max(99) decorators to age
  age: number;
}

Need a hint?

Use these decorators to ensure age is an integer between 18 and 99.