Custom validation decorators in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom validation decorator in NestJS?

A custom validation decorator in NestJS is a user-defined function that adds specific validation rules to class properties, allowing you to check data beyond built-in validators.

beginner

Which package is commonly used to create custom validation decorators in NestJS?

The 'class-validator' package is commonly used to create custom validation decorators in NestJS, enabling easy integration with validation pipes.

intermediate

What are the two main parts needed to create a custom validation decorator in NestJS?

You need a validator constraint class implementing the validation logic and a decorator function that applies this constraint to a property.

intermediate

How do you ensure your custom validator works with NestJS validation pipe?

By using the 'ValidatorConstraint' and 'Validate' decorators from 'class-validator' and applying the custom decorator on DTO properties, the validation pipe automatically runs your custom logic.

beginner

Why might you create a custom validation decorator instead of using built-in ones?

You create custom validation decorators to handle specific rules unique to your app, like checking a username format or verifying a business rule that built-in validators don't cover.

Which decorator marks a class as a custom validator constraint in NestJS?

A @IsString

B @ValidatorConstraint

C @Validate

D @IsNotEmpty

The @ValidatorConstraint decorator marks a class as a custom validator constraint.

What does the @Validate decorator do in a custom validation setup?

A Marks a property as optional

B Defines a new validation rule

C Runs validation on the whole class

D Applies a custom validator to a property

The @Validate decorator applies a custom validator class to a specific property.

Which package provides the tools to create custom validation decorators in NestJS?

A class-validator

B express-validator

C joi

D nestjs-validation

The class-validator package is used in NestJS for validation decorators.

What must a custom validator class implement to work properly?

A ValidatorConstraintInterface

B ValidationPipe

C PipeTransform

D OnModuleInit

The custom validator class must implement ValidatorConstraintInterface.

Why use custom validation decorators in NestJS?

A To replace the validation pipe

B To speed up the app

C To validate data with rules not covered by built-in validators

D To style the UI

Custom validation decorators allow validation of specific rules not covered by built-in validators.

Explain how to create a custom validation decorator in NestJS step-by-step.

Think about the class-validator decorators and how they connect.

Describe why and when you would use a custom validation decorator in a NestJS project.

Consider unique app requirements and validation needs.