How do you write a custom class-validator decorator in NestJS?

Q: How do you write a custom class-validator decorator in NestJS?

import { ValidatorConstraint, ValidatorConstraintInterface, ValidationArguments, registerDecorator } from 'class-validator'; // 1. Define the constraint class @ValidatorConstraint({ name: 'isStrongPassword', async: false }) export class IsStrongPasswordConstraint implements ValidatorConstraintInterface { validate(value: string, args: ValidationArguments): boolean { return /[A-Z]/.test(value) && /[0-9]/.test(value) && /[!@#$]/.test(value); } defaultMessage(args: ValidationArguments): string { return `${args.property} must contain uppercase, digit, and special character`; } } // 2. Create the convenience decorator export function IsStrongPassword() { return function (object: object, propertyName: string) { registerDecorator({ target: object.constructor, propertyName, validator: IsStrongPasswordConstraint, }); }; } // 3. Use it on a DTO export class RegisterDto { @IsStrongPassword() password: string; } 1. Create a class implementing ValidatorConstraintInterface with validate() and defaultMessage(). 2. Decorate it with @ValidatorConstraint({ name: 'uniqueName', async: false }). 3. Create a convenience function that calls registerDecorator() with the constraint. 4. ValidationArguments gives access to value, property, object, and constraints. Set async: true on @ValidatorConstraint for validators that perform async operations like DB queries.

Difficulty: 5/10

custom decorator, validation pipeline, async validation

Implement ValidatorConstraintInterface and register it with @ValidatorConstraint, then create a convenience decorator using registerDecorator. The constraint class contains the validate() logic and defaultMessage() for the error text.

Custom @IsStrongPassword() validator

Custom decorator creation steps:

1
1. Create a class implementing ValidatorConstraintInterface with validate() and defaultMessage().
2

How do you write a custom class-validator decorator in NestJS?

Difficulty: 5/10

custom decorator, validation pipeline, async validation

Implement ValidatorConstraintInterface and register it with @ValidatorConstraint, then create a convenience decorator using registerDecorator. The constraint class contains the validate() logic and defaultMessage() for the error text.

Custom @IsStrongPassword() validator

Custom decorator creation steps:

1
1. Create a class implementing ValidatorConstraintInterface with validate() and defaultMessage().
2

How do you write a custom class-validator decorator in NestJS?

Implement ValidatorConstraintInterface and register it with @ValidatorConstraint, then create a convenience decorator using registerDecorator. The constraint class contains the validate() logic and defaultMessage() for the error text.

How do you write a custom class-validator decorator in NestJS?

Implement ValidatorConstraintInterface and register it with @ValidatorConstraint, then create a convenience decorator using registerDecorator. The constraint class contains the validate() logic and defaultMessage() for the error text.

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