Why pipes transform and validate input in NestJS - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply a built-in validation pipe to the controller method.

NestJS

import { Controller, Post, Body, [1] } from '@nestjs/common';

@Controller('users')
export class UsersController {
  @Post()
  createUser(@Body(new [1]()) userData: any) {
    return userData;
  }
}

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AUseGuards

BValidationPipe

CParseIntPipe

DHttpException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pipe that only parses numbers instead of validating the whole object.

Forgetting to instantiate the pipe with parentheses.

The ValidationPipe is used to automatically validate and transform incoming data in NestJS controllers.

2fill in blank

medium

Complete the code to transform the input string to a number using a pipe.

NestJS

import { Controller, Get, Param, [1] } from '@nestjs/common';

@Controller('items')
export class ItemsController {
  @Get(':id')
  getItem(@Param('id', new [1]()) id: number) {
    return { id };
  }
}

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AParseIntPipe

BDefaultValuePipe

CParseBoolPipe

DValidationPipe

Attempts:

3 left

💡 Hint

Common Mistakes

Using ValidationPipe which does not transform types by default.

Not instantiating the pipe with parentheses.

The ParseIntPipe converts the input string parameter to a number, ensuring the controller receives a number type.

3fill in blank

hard

Fix the error in the pipe usage to enable automatic transformation of input data.

NestJS

import { Controller, Post, Body, ValidationPipe } from '@nestjs/common';

@Controller('products')
export class ProductsController {
  @Post()
  addProduct(@Body(new ValidationPipe({ [1]: true })) productData: any) {
    return productData;
  }
}

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Atransform

Bvalidate

CautoTransform

DtransformInput

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect option names that do not exist in ValidationPipe.

Not enabling transformation causes type mismatches.

The transform option enables automatic conversion of input data types in ValidationPipe.

4fill in blank

hard

Fill both blanks to create a custom pipe that validates and transforms input.

NestJS

import { PipeTransform, Injectable, ArgumentMetadata, BadRequestException } from '@nestjs/common';

@Injectable()
export class [1] implements PipeTransform {
  transform(value: any, metadata: ArgumentMetadata) {
    if (typeof value !== '[2]') {
      throw new BadRequestException('Validation failed');
    }
    return value;
  }
}

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AStringValidationPipe

BNumberValidationPipe

Cstring

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between class name and type checked.

Using wrong type string in typeof comparison.

This custom pipe named StringValidationPipe checks if the input is a string and throws an error if not.

5fill in blank

hard

Fill all three blanks to apply a global validation pipe with transformation enabled.

NestJS

import { ValidationPipe, [1] } from '@nestjs/common';
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(new [2]({ [3]: true }));
  await app.listen(3000);
}
bootstrap();

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AINestApplication

BValidationPipe

Ctransform

DParseIntPipe

Attempts:

3 left

💡 Hint

Common Mistakes

Using ParseIntPipe globally instead of ValidationPipe.

Forgetting to enable transform option causes no type conversion.

This code imports INestApplication, applies a global ValidationPipe with the transform option enabled to automatically convert input types.