ValidationPipe in depth in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the ValidationPipe in NestJS?

ValidationPipe automatically checks incoming data against defined rules to ensure it is correct and safe before it reaches your code.

intermediate

How do you enable automatic transformation of input data types using ValidationPipe?

By setting the option { transform: true } when creating the ValidationPipe, NestJS converts input data to the expected types defined in DTO classes.

beginner

What happens if validation fails when using ValidationPipe?

ValidationPipe throws a detailed error response explaining which fields failed and why, preventing the controller from running with bad data.

intermediate

Explain the difference between whitelist and forbidNonWhitelisted options in ValidationPipe.

Whitelist removes any properties not in the DTO from the input. forbidNonWhitelisted throws an error if extra properties are present, helping catch unwanted data.

beginner

How can you apply ValidationPipe globally in a NestJS application?

Use app.useGlobalPipes(new ValidationPipe()) in the main.ts file to apply validation to all incoming requests automatically.

What option must be set to true to convert input strings to expected types in ValidationPipe?

A transform

B whitelist

C forbidNonWhitelisted

D skipMissingProperties

Setting transform: true enables automatic type conversion of input data.

Which ValidationPipe option removes properties not defined in the DTO?

A forbidNonWhitelisted

B transform

C stopAtFirstError

D whitelist

Whitelist removes extra properties from the input data.

What does ValidationPipe do if input data fails validation?

A Throws an error and stops request processing

B Logs errors but continues

C Ignores errors and passes data

D Automatically fixes errors

ValidationPipe throws an error to prevent bad data from reaching your code.

How do you apply ValidationPipe to all routes in a NestJS app?

A Add ValidationPipe to each controller method

B Set validation in DTO classes only

C Use app.useGlobalPipes(new ValidationPipe()) in main.ts

D Import ValidationPipe in every module

Using app.useGlobalPipes applies ValidationPipe globally.

What does forbidNonWhitelisted option do in ValidationPipe?

A Automatically adds missing properties

B Throws an error if extra properties exist

C Removes extra properties silently

D Ignores validation errors

forbidNonWhitelisted causes validation to fail if unexpected properties are present.

Describe how ValidationPipe helps keep your NestJS app safe and clean.

Think about how ValidationPipe acts like a gatekeeper for incoming data.

Explain the difference between using whitelist and forbidNonWhitelisted options in ValidationPipe.

One quietly cleans input, the other loudly complains.