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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 install 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 '@globalart/nestcord';

@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