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Validation

COMET DXP provides custom validation decorators for use with class-validator in NestJS DTOs.

@IsUndefinable()​

Use @IsUndefinable() to allow a field to be undefined while still validating it when a value is provided.

This is more specific than the @IsOptional() decorator from class-validator, which allows both undefined and null.

A typical use case is a small inline form that only updates a subset of an entity's fields (e.g., only the name). Fields not present in the form are omitted from the request body entirely (undefined) and should be left unchanged on the server.

import { IsUndefinable } from "@comet/cms-api";
import { IsString } from "class-validator";

class UpdateProductInput {
    @IsUndefinable()
    @IsString()
    name?: string;

    @IsUndefinable()
    @IsString()
    description?: string;
}

@IsNullable()​

Use @IsNullable() to allow a field to be null while still validating it when a value is provided.

This is more specific than the @IsOptional() decorator, which also allows undefined.

A typical use case is resetting or clearing an optional value (e.g., removing a product's assigned category).

import { IsNullable } from "@comet/cms-api";
import { IsString } from "class-validator";

class UpdateProductInput {
    @IsNullable()
    @IsString()
    category: string | null;
}

Replacing @IsOptional()​

The @IsOptional() decorator from class-validator allows both undefined and null. This can lead to unintentional bugs.

Use @IsUndefinable() or @IsNullable() to be more specific about which values are allowed:

DecoratorAllows undefinedAllows null
@IsOptional()✅✅
@IsUndefinable()✅❌
@IsNullable()❌✅

PartialType​

COMET DXP provides its own PartialType helper (from @comet/cms-api) that uses @IsUndefinable() instead of @IsOptional().

When creating partial input types, use PartialType from @comet/cms-api instead of @nestjs/mapped-types:

import { PartialType } from "@comet/cms-api";

import { CreateProductInput } from "./create-product.input";

export class UpdateProductInput extends PartialType(CreateProductInput) {}