question: nested validation but discriminated depending on a field value in the root dto about class-validator

[emir-gradient]

Hi.

Since you are utilizing class-transformer, @Type decorator from class-transformer could work for you.

You need:

class RootDto {
    @IsNumber()
    id : number,
    @IsString()
    description : string,
    @IsString()
    type : string,
    
    @ValidateNested()
    @Type(typeHelpOptions => {
        const type = typeHelpOptions.object.type; // attribute type value from the object.
        switch (type) {
          case 'TypeOne':
            return TypeOneDto;
          case 'TypeTwo':
            return TypeTwoDto;
          case 'TypeThree':
            return TypeThreeDto;
          default:
            throw new Error(`No matching class found for: ${type}`);
        }
      })
    metadata : TypeOneDto | TypeTwoDto | TypeThreeDto
}

Important: For this to work, your object, must go through class-transformer method plainToClass. For example, if you are using Nest, it should already happen. But, in general, if you are manually instantiating class and filling with plain object, then @Type won't even get executed, hence, won't work.

[mdhthahmd]

Hi @emir-gradient ,
Yes this is with nestjs and your solution seems to work well, i did add @IsObject() decorator to make metadata field required.

Thanks.

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