SilverStripe 3.x DataObject as Page with URLSegment

DataObjectAsPage.php

<?php

/**
 * @author Zauberfisch
 * @method ManyManyList Products()
 */
class ProductCategoryPage extends Page {
	private static $many_many = array(
		'Products' => 'Product',
	);
	private static $many_many_extraFields = array(
		'Products' => array(
			'SortOnPage' => 'Int',
		),
	);
	private static $allowed_children = 'none';

	public function getCMSFields() {
		$fields = parent::getCMSFields();
		$fields->addFieldToTab('Root', Tab::create('Products', $this->fieldLabel('ProductsTab')));
		$fields->addFieldToTab('Root.Products', GridField::create(
			'Products',
			$this->fieldLabel('Products'),
			$this->Products(),
			GridFieldConfig::create()
				->addComponent(new GridFieldButtonRow('before'))
				->addComponent(new GridFieldAddExistingAutocompleter('buttons-before-left'))
				->addComponent(new GridFieldDataColumns())
				->addComponent(new GridFieldOrderableRows('SortOnPage'))
				->addComponent(new GridFieldTitleHeader())
				->addComponent(new GridFieldDeleteAction(true))
		));
		return $fields;
	}

	public function fieldLabels($includerelations = true) {
		$return = parent::fieldLabels($includerelations);
		$return['ProductsTab'] = _t('ProductCategoryPage.ProductsTab', 'Products');
		$return['Products'] = _t('ProductCategoryPage.Products', 'Products');
		return $return;
	}

	public function SubMenu() {
		if ($this->isSection()) {
			$menu = ArrayList::create();
			foreach ($this->Products() as $item) {
				$menu->push($item->customise(array(
					// to allow <% if $Current %> in templace
					'Current' => $item->ID == ProductCategoryPage_Controller::$current_product_id
				)));
			}
			return $menu;
		} else {
			return $this->Products();
		}
	}
}

/**
 * @author Zauberfisch
 */
class ProductCategoryPage_Controller extends Page_Controller {
	public static $current_product_id;
	private static $allowed_actions = array(
		'product'
	);

	public function product(SS_HTTPRequest $r) {
		$p = Product::get_by_url_segment(Convert::raw2sql($r->param('ID')));
		if (!$p) {
			return ErrorPage::responseFor(404);
		}
		static::$current_product_id = $p->ID;
		return $this->customise($p)->renderWith(array('Product', 'Page'));
	}
}

/**
 * @author Zauberfisch
 * @property Varchar Title
 * @property Varchar MenuTitle
 * @property HTMLText Content
 * @property Varchar URLSegment
 * @method ManyManyList Categories
 */
class Product extends DataObject {
	private static $db = array(
		'Title' => 'Varchar(255)',
		'MenuTitle' => 'Varchar',
		'Content' => 'HTMLText',
		'URLSegment' => 'Varchar(255)',
	);
	private static $belongs_many_many = array(
		'Categories' => 'ProductCategoryPage',
	);
	private static $summary_fields = array(
		'Title',
		'URLSegment',
	);

	public function getCMSFields() {
		return new FieldList(array(
			TextField::create('Title', $this->fieldLabel('Title')),
			TextField::create('MenuTitle', $this->fieldLabel('MenuTitle')),
			TextField::create('URLSegment', $this->fieldLabel('URLSegment')),
			// ListboxField::create('Categories', _t('Product.Categories', 'Categories'))->setMultiple(true)->setSource(CategoryPage::get()->map('ID', 'MenuTitle')->toArray()),
			HTMLEditorField::create('Content', $this->fieldLabel('Content')),
		));
	}

	public function fieldLabels($includerelations = true) {
		$return = parent::fieldLabels($includerelations);
		$return['Title'] = _t('Product.Title', 'Title');
		$return['MenuTitle'] = _t('Product.MenuTitle', 'Menu Title');
		$return['URLSegment'] = _t('Product.URLSegment', 'URL Segment');
		$return['Content'] = _t('Product.Content', 'Content');
		return $return;
	}

	protected function onBeforeWrite() {
		parent::onBeforeWrite();
		if (!$this->MenuTitle) {
			$this->MenuTitle = $this->Title;
		}
		$filter = URLSegmentFilter::create();
		if (!$this->URLSegment) {
			$this->URLSegment = $this->Title;
		}
		$this->URLSegment = $filter->filter($this->URLSegment);
		if (!$this->URLSegment) {
			$this->URLSegment = uniqid();
		}
		$count = 2;
		while (static::get_by_url_segment($this->URLSegment, $this->ID)) {
			// add a -n to the URLSegment if it already existed
			$this->URLSegment = preg_replace('/-[0-9]+$/', null, $this->URLSegment) . '-' . $count;
			$count++;
		}
	}

	/**
	 * @return string
	 */
	public function Link() {
		if ($this->isInDB()) {
			$controller = Controller::curr();
			if ($controller->is_a('ProductCategoryPage') &&
				$controller->data() &&
				$this->Categories()->byID((int)$controller->data()->ID)->exists()
			) {
				// this product is in this category, so lets use this category as link
				$category = $controller->data();
			} elseif ($this->Categories()->count()) {
				$category = $this->Categories()->First();
			} else {
				$category = ProductCategoryPage::get()->First();
			}
			if ($category && $category->exists()) {
				return Controller::join_links($category->Link(), 'product', $this->URLSegment);
			}
		}
		return '';
	}

	/**
	 * @var array
	 */
	protected static $_cached_get_by_url = array();

	/**
	 * @param $str
	 * @return Product|Boolean
	 */
	public static function get_by_url_segment($str, $excludeID = null) {
		if (!isset(static::$_cached_get_by_url[$str])) {
			$list = static::get()->filter('URLSegment', $str);
			if ($excludeID) {
				$list = $list->exclude('ID', $excludeID);
			}
			$obj = $list->First();
			static::$_cached_get_by_url[$str] = ($obj && $obj->exists()) ? $obj : false;
		}
		return static::$_cached_get_by_url[$str];
	}
}