Pipes

A pipe is a class which implements the PipeTransform interface.

Pipes have two typical use cases:

• transformation: transform input data to the desired form (e.g., from string to integer)
• validation: evaluate input data and if valid, simply pass it through unchanged; otherwise, throw an exception

The built-in ValidationPipe

The ValidationPipe is provided by Fastwa out-of-the-box. The built-in ValidationPipe offers more options than the sample we built in this chapter, which has been kept basic for the sake of illustrating the mechanics of a custom-built pipe.

Class validator

Let's look at an alternate implementation for our validation technique.

1import { IsString, IsEmail } from 'class-validator';
2

3export class CreateUserDto {
4  @IsString()
5  name: string;
6

7  @IsEmail()
8  email: string;
9}

Good to know: Read more about the class-validator decorators here.

Global scoped pipes

We can realize it's full utility by setting it up as a global-scoped pipe so that it is applied to every command handler across the entire application.

1async function bootstrap() {
2  const { version } = await fetchLatestBaileysVersion();
3  const { state, saveCreds } = await useMultiFileAuthState('./sessions');
4

5  const app = await WAFactory.create(AppModule, {
6    version,
7    auth: state,
8    printQRInTerminal: true,
9    saveCreds
10  });
11

12  app.useGlobalPipes(new ValidationPipe());
13

14  await app.listen();
15}
16bootstrap();