Validation with Joi in NestJS - Mini Project: Build & Apply

Validation with Joi in NestJS

📖 Scenario: You are building a simple NestJS API to register users. You want to make sure the data sent by clients is correct before saving it.

🎯 Goal: Create a Joi validation schema to check user data, then apply it in a NestJS DTO to validate incoming requests.

📋 What You'll Learn

Create a Joi schema for user data with exact fields

Add a configuration variable for minimum password length

Use the Joi schema in a NestJS DTO class

Apply the validation pipe in the controller method

💡 Why This Matters

🌍 Real World

Validating user input is essential in APIs to prevent bad data and security issues. Joi is a popular library for this in Node.js and NestJS.

💼 Career

Backend developers often use validation libraries like Joi to ensure data integrity and improve API reliability.

1

Create Joi schema for user data

Create a constant called userSchema using Joi.object() with these exact fields: username as a required string, email as a required string with email format, and password as a required string.

NestJS

# Your code here

Need a hint?

Use Joi.object() to define the schema and Joi.string().required() for each field. For email, add .email().

2

Add minimum password length configuration

Create a constant called MIN_PASSWORD_LENGTH and set it to 8. Then update the password field in userSchema to require a minimum length using .min(MIN_PASSWORD_LENGTH).

NestJS

import * as Joi from 'joi';

export const userSchema = Joi.object({
  username: Joi.string().required(),
  email: Joi.string().email().required(),
  password: Joi.string().required(),
});

# Your code here

Need a hint?

Define MIN_PASSWORD_LENGTH as 8, then use .min(MIN_PASSWORD_LENGTH) on the password field.

3

Use Joi schema in NestJS DTO

Create a class called CreateUserDto. Add a static property called schema and assign it the userSchema constant.

NestJS

import * as Joi from 'joi';

export const MIN_PASSWORD_LENGTH = 8;

export const userSchema = Joi.object({
  username: Joi.string().required(),
  email: Joi.string().email().required(),
  password: Joi.string().min(MIN_PASSWORD_LENGTH).required(),
});

# Your code here

Need a hint?

Create a class and add a static property schema that points to userSchema.

4

Apply validation pipe in controller

In a NestJS controller method called createUser, use the @UsePipes(new JoiValidationPipe(CreateUserDto.schema)) decorator above the method. The method should accept a parameter createUserDto of type CreateUserDto.

NestJS

import * as Joi from 'joi';
import { Controller, Post, Body, UsePipes } from '@nestjs/common';

export const MIN_PASSWORD_LENGTH = 8;

export const userSchema = Joi.object({
  username: Joi.string().required(),
  email: Joi.string().email().required(),
  password: Joi.string().min(MIN_PASSWORD_LENGTH).required(),
});

export class CreateUserDto {
  static schema = userSchema;
}

@Controller('users')
export class UsersController {
  
  # Your code here
}

Need a hint?

Use @UsePipes(new JoiValidationPipe(CreateUserDto.schema)) above the createUser method and accept createUserDto as a parameter with @Body().