code: public function getDataAttributes($excludeExtended = false) 
      {
          $attributes = new \Cora\Collection();
  
          foreach ($this->model_attributes as $key => $def) {
              if (!isset($def['model']) && !isset($def['models'])) {
                  $attributes->add($key);
              }
          }
  
          if (isset($this->model_extends) && isset($this->model_attributes[$this->model_extends])) {
              $extendedModel = $this->{$this->model_extends};
              if ($extendedModel) {
                  $attributes->merge($extendedModel->getDataAttributes());
              }
          }
          return array_unique($attributes->toArray());
      }
docs: Fetches a collection of the data attributes that apply to this model.
  Does not include relationships. Will included extended fields unless set to exclude.
  
  @param boolean $excludeExtended Whether or not to exclude extended data elements. Defaults to false.
  @return \Cora\Collection