silverstripe-cms/code/model/SiteTreeFileExtension.php

<?php
/**
 * @package cms
 * @subpackage model
 */
class SiteTreeFileExtension extends DataExtension {

	private static $belongs_many_many = array(
		'BackLinkTracking' => 'SiteTree'
	);

	public function updateCMSFields(FieldList $fields) {
		$fields->insertAfter(new ReadonlyField('BackLinkCount', 
			_t('AssetTableField.BACKLINKCOUNT', 'Used on:'), 
			$this->BackLinkTracking()->Count() . ' ' . _t('AssetTableField.PAGES', 'page(s)')), 
			'LastEdited'
		);
	}

	/**
	 * Extend through {@link updateBackLinkTracking()} in your own {@link Extension}.
	 * 
	 * @return ComponentSet
	 */
	public function BackLinkTracking($filter = "", $sort = "", $join = "", $limit = "") {
		if(class_exists("Subsite")){
			$rememberSubsiteFilter = Subsite::$disable_subsite_filter;
			Subsite::disable_subsite_filter(true);
		}
		
		$links = $this->owner->getManyManyComponents('BackLinkTracking', $filter, $sort, $join, $limit);
		$this->owner->extend('updateBackLinkTracking', $links);
		
		if(class_exists("Subsite")){
			Subsite::disable_subsite_filter($rememberSubsiteFilter);
		}
		
		return $links;
	}
	
	/**
	 * @todo Unnecessary shortcut for AssetTableField, coupled with cms module.
	 * 
	 * @return Integer
	 */
	public function BackLinkTrackingCount() {
		$pages = $this->owner->BackLinkTracking();
		if($pages) {
			return $pages->Count();
		} else {
			return 0;
		}
	}
	
	/**
	 * Updates link tracking.
	 */
	public function onAfterDelete() {
	    // We query the explicit ID list, because BackLinkTracking will get modified after the stage
	    // site does its thing
		$brokenPageIDs = $this->owner->BackLinkTracking()->column("ID");
		if($brokenPageIDs) {
			$origStage = Versioned::current_stage();

			// This will syncLinkTracking on draft
			Versioned::reading_stage('Stage');
			$brokenPages = DataObject::get('SiteTree')->byIDs($brokenPageIDs);
			foreach($brokenPages as $brokenPage) $brokenPage->write();

			// This will syncLinkTracking on published
			Versioned::reading_stage('Live');
			$liveBrokenPages = DataObject::get('SiteTree')->byIDs($brokenPageIDs);
			foreach($liveBrokenPages as $brokenPage) {
			    $brokenPage->write();
		    }

			Versioned::reading_stage($origStage);
		}
	}
	
	/**
	 * Rewrite links to the $old file to now point to the $new file.
	 * 
	 * @uses SiteTree->rewriteFileURL()
	 * 
	 * @param String $old File path relative to the webroot
	 * @param String $new File path relative to the webroot
	 */
	public function updateLinks($old, $new) {
		if(class_exists('Subsite')) Subsite::disable_subsite_filter(true);
	
		$pages = $this->owner->BackLinkTracking();

		$summary = "";
		if($pages) {
			foreach($pages as $page) $page->rewriteFileURL($old,$new);
		}
		
		if(class_exists('Subsite')) Subsite::disable_subsite_filter(false);
	}
	
}