Silverstripe GalleryPic Dataobject with Shortcodable interface

GalleryPic.php

<?php

/**
 * Class GalleryPic
 * @todo: sync Copyright if Image has a db field for it
 */
class GalleryPic extends DataObject implements Shortcodable
{
	private static $db = array(
		'Title' => 'Text',
		'Description' => 'Text',
		'Copyright' => 'Text',
		'SortOrder' => 'Int'
	);

	private static $has_one = array(
		'Attachment' => 'Image',
		'ResourcePage' => 'Page'
	);

	private static $default_sort = 'SortOrder';

	private static $singular_name = 'Galeriebild';
	private static $plural_name = 'Galeriebilder';

	public function getCMSFields()
	{
		$fields = new FieldList(
			TextField::create('Title', 'Titel'),
			TextareaField::create('Description', 'Beschreibung'),
			TextField::create('Copyright', 'Copyright / Quelle'),
			$imageField = UploadField::create('Attachment')
		);
		$imageField->setAllowedFileCategories('image');
		$imageField->setAllowedMaxFileNumber(1);

		$this->extend('updateCMSFields', $fields);
		return $fields;

	}

	/**
	 * @inheritdoc
	 * @return Fieldlist|void
	 */
	public static function shortcode_attribute_fields()
	{
		return FieldList::create(
			TextField::create('Text','Text')
		);
	}

	/**
	 * Parse the shortcode and render as a string
	 * @param array $arguments the list of attributes of the shortcode
	 * @param string $content the shortcode content
	 * @param ShortcodeParser $parser the ShortcodeParser instance
	 * @param string $shortcode the raw shortcode being parsed
	 * @return String
	 **/
	public static function parse_shortcode($arguments, $content, $parser, $shortcode){
		if (isset($arguments['Text']) &&
			isset($arguments['id']) &&
			$img = GalleryPic::get()->byID($arguments['id'])) {
				return '<span data-rel-imgid="' . $img->ID . '">' . $arguments['Text'] . '</span>';
		}
	}

	/**
	 * returns the records for shortcode form
	 * @return array
	 */
	public static function get_shortcodable_records() {
		$currentPage = $_SESSION['CMSMain']['currentPage'];
		return	GalleryPic::get()
					->filter(array('ResourcePageID' => $currentPage))
					->map()
					->toArray();
		}
}