CODEWITHSUNDEEP
typescriptnestedclass-transformer
oktapodia
oktapodia

Reputation: 1758

class-transformer Transform nested class

I am trying to do a Transformation of an input object to a Dto.

//input object
const input = {
"steps": [{ "id": 1}, {"id": 2}],
"foo": "bar",
"currentStep": {"id": 1}
}

So I have created those DTO classes

import { Expose, Transform, Type } from 'class-transformer';

export class StepDTO {
  @Expose()
  @Transform(({ obj }) => obj.id)
  transformedFoo: number;

}

export class MainDTO {
  @Expose()
  @Transform(({ obj }) => obj.foo)
  transformedFoo: number;

  @Expose()
  @Transform(({ obj }) => obj.steps)
  @Type(() => StepDTO)
  updatedSteps: StepDTO[];

  @Expose()
  @Transform(({ obj }) => obj.steps[0])
  @Type(() => StepDTO)
  currentStep: StepDTO;
}

    const transformed = plainToInstance(
      MainDTO,
      input,
      {
        excludeExtraneousValues: true,
      },
    );

But unfortunately, the result looks like this

{"transformedFoo":"bar","updatedSteps":[{"id":1,"test":"1"},{"id":2,"test":"2"}],"currentStep":{"id":1,"test":"1"}}

It is perfectly working on the main DTO but not onto the nested ones.

I found a solution which does not sound optimal to me by replacing the updatedSteps transform by

  @Expose()
  @Transform(({ obj }) =>
    plainToInstance(StepDTO, obj.steps, { excludeExtraneousValues: true })
  )
  @Type(() => StepDTO)
  updatedSteps: StepDTO[];

Any better idea?

Here's a codesandbox showing the issue https://codesandbox.io/p/devbox/class-transformer-forked-jtkm9n?workspaceId=ws_FXWvFqR2ZwREcHThAQPtQx

Thanks in advance!

Upvotes: 1

Views: 14

Answers (0)

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