Discussion on: Validating numeric query parameters in NestJS

[Krzysztof Szala]

Hi! Thank you for your comment. I'm not sure what do you want to achive with your code example. Could you give me an example of URL and final object with values you want to get? Regards!

[sebytab]

Just try with some boolean param, or even an array.

export class FilterQuery {
@IsOptional()
@IsBoolean()
@Type(() => Boolean)
prova?: boolean
}

Setting 'prova' as 'false' it will cast it to true. As you said, those query params are just strings that must be serialized first in some way. So, in some cases like Number it just works but in others it follows JS conversion rules... I partially solved it doing using @Transform instead of @Type and looking Nestjs parse implementations github.com/nestjs/nest/tree/99ee3f...

[Krzysztof Szala]

You are totally right! And this is the reason why this article is titled “Validating numeric query params” 😁 I think it’s the most common issue Nest users encounter (at least in my experience).

For array of values in query params I use (exactly as you said) Transform decorator from class-transform package. For bools I prefer to pass just boolean in numeric form (0 or 1) or (depends on context) simple string like yes/no. But I avoid true/false, because as you noted – it can result with some false positives.

Anyway, thank you for your comment, I’m sure somebody finds it helpful! Cheers!

[sebytab]

Thank you for the article, it's my first time with Nestjs and I was looking for how to parse & validate params declaratively and without too many hustles. I hadn't noticed "numeric" in the title, sorry 😅
How do you manage arrays, i.e. numeric[] ? At the moment I use ParseArray (that also is the only Parse* function that can handle natively missing query params)

[Krzysztof Szala]

I've struggled with arrays a lot, and ended up with some like this. I'm not very proud of it, but it works for me.

I decorate expected field with:

@IsArray()
@Transform(({ value }) => (value ? Transformation.mapStringToNumber(value) : undefined))
categories: number[];

And here is mapStringToNumber implementation:

export class Transformation {
  static mapStringToNumber(value: string | string[]): number[] | undefined {
    const explodedValues = typeof value === 'string' ? value.split(',') : value;
    const filteredValues = explodedValues.filter(Number).map(Number);

    return filteredValues.length > 0 ? filteredValues : undefined;
  }
}

It allows me to pass array of numbers and just string with numbers separated with commas as well. It also cleans up non-numeric values. So, when you pass e.g. categories=1,a,2, you will get an array of [1,2].

I'm not the biggest fan of using extra pipes for validating. I rather try to keep my validation in one place (in validation class with class-validator in this case).