Validation

The ValidationPipe is a built-in pipe that can be used to validate data coming from the client. It uses class-validator package under the hood. The ValidationPipe provides a convenient approach to enforce validation rules for all incoming client payloads, where the specific rules are declared with simple annotations in DTO declarations in each module.

Installation

npm

$ npm install class-validator class-transformer

Yarn

$ yarn add class-validator class-transformer

pnpm

$ pnpm add class-validator class-transformer

Usage

Now we can add a few validation rules in our CreateUserDto. We do this using decorators provided by the class-validator package, described in detail here. In this fashion, any route that uses the CreateUserDto will automatically enforce these validation rules.

src/users/dto/create-user.dto.ts

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

export class CreateUserDto {
    @StringOption({
        name: 'name',
        description: 'Your name',
        required: true
    })
    name: string;

    @IsEmail()
    @StringOption({
        name: 'text',
        description: 'Your email',
        required: false
    })
    email: string;
}

tip

Also you can use ValidationPipe for transforming and validating the payload of a request.

Read more about transforming

Now, we can use the ValidationPipe in our UsersCommands to enforce the validation rules we just defined.

src/users/users.commands.ts

import { Injectable } from '@nestjs/common';
import { Context, SlashCommand, SlashCommandContext } from 'necord';

@Injectable()
export class UsersCommands {
    @SlashCommand({
        name: 'create',
        description: 'Create a new user'
    })
    public async onCreateUser(
        @Context() [interaction]: SlashCommandContext,
        @Options(new ValidationPipe({ validateCustomDecorators: true })) createUserDto: CreateUserDto
    ) {
        return interaction.reply({ content: `User created: ${createUserDto.name}` });
    }
}

Now, if we try to use the create command without providing a name or email, we will get an error message.

{"statusCode":400,"message":["email should not be empty"],"error":"Bad Request"}

You can create snippet for validated options decorator:

src/decorators/validated-options.decorator.ts

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

export const ValidatedOptions = (...dataOrPipes: PipeTransform[] | string) => {
    return Options(...dataOrPipes, new ValidationPipe());
};

tip

You can create filters to handle and response validation errors.

See Exception Filters for more information