ValidationPipe setup in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of ValidationPipe in NestJS?

ValidationPipe automatically checks incoming data against defined rules to ensure it is valid before processing. It helps catch errors early and keeps the app safe.

beginner

How do you apply ValidationPipe globally in a NestJS application?

Use app.useGlobalPipes(new ValidationPipe()) inside the main.ts file after creating the app instance.

beginner

Which package must be installed to use ValidationPipe with decorators like @IsString()?

You need to install class-validator and class-transformer packages to use ValidationPipe with decorators.

intermediate

What does the 'whitelist' option do in ValidationPipe?

It removes any properties from the input object that are not defined in the DTO, helping to keep data clean and safe.

intermediate

How can you enable automatic transformation of input data types in ValidationPipe?

Set the 'transform' option to true in ValidationPipe. This converts input strings to the expected types defined in DTOs.

Where do you typically set up ValidationPipe globally in a NestJS app?

A Inside each controller method

B In main.ts using app.useGlobalPipes()

C In the service class constructor

D In the module imports array

Global pipes like ValidationPipe are set up in main.ts with app.useGlobalPipes() to apply validation app-wide.

Which decorator is used to mark a class property as a string for validation?

A @IsString()

B @IsBoolean()

C @IsNumber()

D @IsDate()

@IsString() marks a property to be validated as a string using class-validator.

What happens if ValidationPipe receives invalid data?

A It throws a BadRequestException

B It silently ignores the error

C It logs a warning but continues

D It converts data to default values

ValidationPipe throws a BadRequestException when validation fails, stopping the request.

What does setting 'forbidNonWhitelisted' to true do in ValidationPipe?

A Ignores validation rules

B Removes extra properties silently

C Allows extra properties without error

D Throws an error if extra properties exist

'forbidNonWhitelisted: true' causes ValidationPipe to throw an error if unknown properties are present.

Which packages are required to use ValidationPipe decorators?

A express and body-parser

B typeorm and graphql

C class-validator and class-transformer

D rxjs and reflect-metadata

class-validator and class-transformer provide decorators and transformation support for ValidationPipe.

Explain how to set up ValidationPipe globally in a NestJS app and why it is useful.

Think about where the app starts and how to apply validation everywhere.

Describe the purpose of the 'whitelist' and 'transform' options in ValidationPipe.

Consider how these options clean and convert data.