How can I create custom validators in TypeScript using class-validator?

How can I create custom validators in TypeScript using class-validator?

You can create custom validators in TypeScript using the class-validator library by defining a new validation decorator. Would you like a code example?

Yes, please provide a code example.

Sure! Here's a simple example:

import { registerDecorator, ValidationOptions, ValidatorConstraint, ValidatorConstraintInterface } from 'class-validator';

@ValidatorConstraint({ async: false })
class IsPositiveConstraint implements ValidatorConstraintInterface {
    validate(value: number) {
        return value > 0;
    }
}

export function IsPositive(validationOptions?: ValidationOptions) {
    return function (object: Object, propertyName: string) {
        registerDecorator({
            name: 'isPositive',
            target: object.constructor,
            propertyName: propertyName,
            options: validationOptions,
            validator: IsPositiveConstraint,
        });
    };
}

This code defines a custom validator that checks if a number is positive.

How do I use this custom validator in a class?

You can use the custom validator in a class like this:

import { IsPositive } from './path-to-your-validator';

class Product {
    @IsPositive({ message: 'Price must be a positive number' })
    price: number;
}

Now, when you validate an instance of Product, it will check if the price is positive.