Get property from nested object

Question

I have this DTO:

import { Expose, Type } from 'class-transformer';
import { UserDto } from '../../../admin/users/dtos/user.dto';

export class CompanyDto {
  constructor(partial: Partial<CompanyDto>) {
    Object.assign(this, partial);
  }

  @Expose()
  id!: number;

  @Expose()
  companyName!: string;

  @Expose()
  companyCode!: string;

  @Expose()
  country!: string;

  @Expose()
  headQuarter!: string;

  @Expose()
  @Type(() => UserDto)
  user!: UserDto;

  @Expose()
  createdBy!: string;

  @Expose()
  createdAt!: Date;
}

This is the object from the DB:

id: 12,
companyName: 'some company',
companyCode: '0001',
country: 'germany',
headQuarter: 'berlin',
createdAt: 2025-04-26T11:31:57.891Z,
user: User { userName: 'a12' }

I convert this into the DTO:

  plainToInstance(CompanyDto, new CompanyDto(company), {
    excludeExtraneousValues: true,
  }),

And I get a JSON like this:

"id": 12,
"companyName": "some company",
"companyCode": "0001",
"country": "germany",
"headQuarter": "berlin",
"user": {
    "userName": "a12"
},
"createdAt": "2025-04-26T11:31:57.891Z"

Instead of the user object, I only need a new property createdBy, which has the value of userName. I tried with getter, I tried with transform, no success. How can I get the content of the userName in the field createdBy?

There is no debug details, no errors, etc. I simply don't get in the JSON the createdBy field with its data.

Bassem Ben Ghorbel · Accepted Answer · 2025-04-26 17:29:45Z

0

You said that you tried with getter but wasn't successfull, I will quote what was said in this answer. plainToInstance will return an instance so you won't be able to see the computed getter property. To do so, use instanceToPlain which is meant to serialize that object.

answered Apr 26 at 17:29

Bassem Ben Ghorbel

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Comments

derstauner · Accepted Answer · 2025-04-27 06:06:43Z

0

This did the trick:

 @Expose()
  @Transform(({ obj }) => obj.user.userName)
  createdBy!: string;

answered Apr 27 at 6:06

derstauner

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