How do I transform a MongoDB document into a NestJS DTO?

Question

I have a data layer that reads and writes to a MongoDB instance. I only want to deal with MongoDB documents at that layer and not expose that implementation to my services.

Right now I am doing something like:

// users.repository.ts

...
async getUserById(id: string): Promise<UserDto> {
  const user = await this.model.findOne({ _id: id }).exec();
  return this.transformToDto(user);
}

private transformToDto(user: UserDocument): UserDto {
  return {
    id: user._id,
    ...etc
  }
}

...

This seems overly verbose and there must be a simpler way to achieve this without adding a helper to every repository.

Is there a cleaner way to achieve this?