Validating a nested object with a property from the parent

[markjaniczak]

There doesn't seem to be a straight forward way of validating a nested object based on a property from its parent or further up the tree. I'm looking for guidance on the best way to achieve this.

For example, I have the following object from a form:

{
    "name": "My Video Stream",
    "hasRedundancy": true,
    "source": {
        "type": "hls",
        "primary": "https://some-domain.com/index.m3u8",
        "secondary": "https://some-domain.com/backup.m3u8"
    }
}

The secondary property in the source object is only required if has_redundancy is true. So I write my classes like so:

const SOURCE_TYPES = ['HLS', 'MP4'] as const

type SourceType = (typeof SOURCE_TYPES)[number]

class Source {
    type: SourceType
    primary: any
    secondary: any
}

class HLSSource extends Source {
    type: 'HLS'

    @IsUrl()
    primary: string

    @ValidateIf((obj) => obj.hasRedundancy)
    @IsUrl()
    secondary: string
}

class MP4Source extends Source {
  type: 'MP4'
  
  @IsUrl()
  primary: string

  @ValidateIf((obj) => obj.hasRedundancy)
  @IsUrl()
  secondary: any;
}

class CreateStreamRequest {
    @IsString()
    name: string

    @IsBoolean()
    hasRedundancy: boolean

    @ValidateNested({
      each: true
    })
    @Type(() => Source, {
      discriminator: {
        property: 'type',
        subTypes: [
          { name: 'MP4', value: MP4Source },
          { name: 'HLS', value: HLSSource}
        ]
      },
      keepDiscriminatorProperty: true
    })
    source: HLSSource | MP4Source
}

But hasRedundancy is not included in the plain object that the my Source is created from, only in the top level plain object that CreateStreamRequest is made from. I thought about using the groups feature to tackle this but that seems like double handling because I already have the data to pass to the condition in the original object. I see that the first parameter in the Type decorator provides some parameters but they are not documented anywhere.

[Iuriiiiiii]

Hi, i have this problem too... the parent information is a relevant data that can't be ignored within a complex custom contraint. What should we do?

[elovin]

I would recursively inject an object reference to the parent into all objects into a property with the @Allow & @IsOptional decorators.

E.g. using @Transform() on a custom property on the root Dto or some custom recursive function.

In case you are using NestJS you could do this with an interceptor and modify the request body directly, this interceptor could then also recursively remove the reference in case it ends up in the response for some reason.