Building Robust APIs with NestJS and Joi

What is NestJS?

NestJS is a popular framework for building scalable and robust applications. It provides a clean architecture based on modules, controllers, and providers to help you get started. NestJS supports TypeScript and vanilla JavaScript, and it doesn’t impose any programming paradigm on you.

What is Joi?

Joi is a widely used Node.js data validation library that provides a simple, intuitive, and readable API to describe data. It’s primarily used to validate data sent from API endpoints and allows you to create blueprints of the data type you want to accept.

Importance of Validation

Validation is an essential security concern when building applications. Without proper validation, your application is vulnerable to injection attacks, which can lead to serious security risks. By validating data, you ensure that only valid data enters your application, preventing potential security breaches.

Implementing Joi in NestJS

To implement Joi in NestJS, you need to install the Joi package and create a custom pipe to validate incoming data.

import { PipeTransform, Injectable, ArgumentMetadata } from '@nestjs/common';
import * as Joi from 'joi';

@Injectable()
export class ValidationPipe implements PipeTransform {
  constructor(private readonly schema: Joi.ObjectSchema) {}

  transform(value: any, metadata: ArgumentMetadata) {
    const result = this.schema.validate(value);
    if (result.error) {
      throw new Error(result.error.message);
    }
    return value;
  }
}

You can then use this pipe in your controllers to validate incoming data:

@Post()
@UsePipes(new ValidationPipe(schema))
async create(@Body() createUserDto: CreateUserDto) {
  // ...
}

Validating Different Data Types

Joi provides various methods for validating different data types, including strings, numbers, booleans, arrays, and objects. Here are a few examples:

Validating a string:

const schema = Joi.string().required();

Validating a number:

const schema = Joi.number().integer().required();

Validating a boolean:

const schema = Joi.boolean().required();

Validating an array:

const schema = Joi.array().items(Joi.string()).required();

Validating an object:

const schema = Joi.object({
  name: Joi.string().required(),
  age: Joi.number().integer().required(),
});