exchange-2.0/app/Http/Resources/DocumentResource.php

<?php

namespace App\Http\Resources;

use Illuminate\Http\Resources\Json\JsonResource;

class DocumentResource extends JsonResource
{
    /**
     * Transform the resource into an array.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return array
     */
    public function toArray($request)
    {
        return [
            'id' => $this->id,
            'document_type' => $this->document_type,
            'reference' => $this->reference,
            'status' => (int) $this->status,
            'approved_by' => (int) $this->approved_by,
            'files' => $this->files()->get()
        ];
    }
}