gistfile1.txt

protected function transformAttribute($attribute)
    {   
        if ($attribute instanceof DateTime) {
            // Convert dates to ISO-8601
            return $attribute->format(\DateTime::ISO8601);
        } elseif ($attribute instanceof RichTextData) {
            // RichTextData
            return $attribute->getRawContent();
        } elseif ($attribute instanceof ElementCriteriaModel) {

            // ElementCriteriaModel
            if ($attribute->elementType instanceof AssetElementType) {
                $asset = $attribute->first();

                return $asset ? UrlHelper::getSiteUrl($asset->getUrl()) : null;
            } elseif ($attribute->elementType instanceof MatrixBlockElementType) {
                $arrBlocks = [];
                foreach ($attribute->find() as $block) {
                    $arrBlocks[] = $this->transformAttribute($block->getContent());
                }

                return $arrBlocks;
            }
        } else {
            return ModelHelper::packageAttributeValue($attribute);
        }
    }