File validation pipe in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a File Validation Pipe in NestJS?

A File Validation Pipe in NestJS is a special class that checks if uploaded files meet certain rules before the app processes them. It helps keep files safe and correct.

beginner

How do you use a File Validation Pipe in a NestJS controller?

You add the pipe to the file upload handler method using the @UsePipes() decorator or directly in the @UploadedFile() decorator to check the file before saving or processing it.

beginner

Which common file properties can a File Validation Pipe check?

It can check file size, file type (like images only), and sometimes file name or content to make sure the file is safe and fits the app's needs.

intermediate

What happens if a file does not pass the validation in a NestJS File Validation Pipe?

The pipe throws an error that stops the request. The user gets a clear message about why the file was rejected, like 'File too large' or 'Invalid file type'.

intermediate

Why is it important to validate files on the server side with a pipe?

Because client checks can be bypassed, server-side validation ensures only safe and expected files are accepted, protecting the app from bad files or attacks.

What is the main role of a File Validation Pipe in NestJS?

A To check uploaded files before processing

B To store files on the server

C To send files to the client

D To rename files automatically

A File Validation Pipe checks files to ensure they meet rules before the app processes them.

Which decorator is commonly used to apply a File Validation Pipe to a file upload method?

A @Post()

B @UseGuards()

C @Get()

D @UsePipes()

The @UsePipes() decorator applies validation pipes like the File Validation Pipe.

What happens if a file fails validation in a NestJS File Validation Pipe?

A An error is thrown and request stops

B The request continues without the file

C The file is saved anyway

D The file is renamed automatically

The pipe throws an error to stop the request and inform the user.

Which file property is NOT typically checked by a File Validation Pipe?

A File size

B File type

C File color

D File name

File color is not a property checked by validation pipes.

Why should file validation happen on the server side?

A Because files are only stored on the server

B Because client-side checks can be bypassed

C Because servers are faster

D Because clients cannot upload files

Server-side validation protects the app from unsafe files even if client checks fail.

Explain how a File Validation Pipe works in NestJS and why it is useful.

Think about what happens before the file is saved or processed.

Describe how to apply a File Validation Pipe to a file upload endpoint in NestJS.

Consider how NestJS pipes are used in controllers.