How To Use Class-validator With NestJS 2023

NestJS is a framework for building efficient, scalable Node.js server-side applications. It uses the popular validation library class-validator to create validation decorators that can be used to validate incoming request payloads.

To use class-validator with NestJS, you will first need to install it as a dependency in your project:

npm install class-validator

Once you have class-validator installed, you can create a validation decorator by importing the @Validate decorator from class-validator. You can then use this decorator to specify the validation constraints for the properties of your class.

For example, consider the following User class:

import { Validate } from 'class-validator';

export class User {
  @Validate(/* validation constraints */)
  name: string;

  @Validate(/* validation constraints */)
  email: string;
}

Here, the @Validate decorator is used to specify validation constraints for the name and email properties of the User class.

To validate an instance of the User class, you can use the validate function from class-validator. This function will return an array of validation errors if the instance fails validation, or an empty array if the instance is valid.

For example:

import { validate } from 'class-validator';

const user = new User();

const errors = await validate(user);

if (errors.length > 0) {
  // validation failed
} else {
  // validation succeeded
}

You can also use the @Validate decorator in combination with NestJS controllers to validate request payloads. For example:

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

@Controller('users')
export class UserController {
  @Post()
  create(@Body() user: User) {
    // user has been validated
  }
}

Here, the create method of the UserController will receive a request body that will be automatically validated using the validation constraints specified in the User class.