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());
    }