Part 1 of 2, moving ResourceLoader*Module classes to their own files - this commit...

[mediawiki.git] / includes / LinksUpdate.php

<?php
/**
 * See docs/deferred.txt
 *
 * @todo document (e.g. one-sentence top-level class description).
 */
class LinksUpdate {

        /**@{{
         * @private
         */
        var $mId,            //!< Page ID of the article linked from
                $mTitle,         //!< Title object of the article linked from
                $mLinks,         //!< Map of title strings to IDs for the links in the document
                $mImages,        //!< DB keys of the images used, in the array key only
                $mTemplates,     //!< Map of title strings to IDs for the template references, including broken ones
                $mExternals,     //!< URLs of external links, array key only
                $mCategories,    //!< Map of category names to sort keys
                $mInterlangs,    //!< Map of language codes to titles
                $mProperties,    //!< Map of arbitrary name to value
                $mDb,            //!< Database connection reference
                $mOptions,       //!< SELECT options to be used (array)
                $mRecursive;     //!< Whether to queue jobs for recursive updates
        /**@}}*/

        /**
         * Constructor
         *
         * @param $title Title of the page we're updating
         * @param $parserOutput ParserOutput: output from a full parse of this page
         * @param $recursive Boolean: queue jobs for recursive updates?
         */
        function __construct( $title, $parserOutput, $recursive = true ) {
                global $wgAntiLockFlags;

                if ( $wgAntiLockFlags & ALF_NO_LINK_LOCK ) {
                        $this->mOptions = array();
                } else {
                        $this->mOptions = array( 'FOR UPDATE' );
                }
                $this->mDb = wfGetDB( DB_MASTER );

                if ( !is_object( $title ) ) {
                        throw new MWException( "The calling convention to LinksUpdate::LinksUpdate() has changed. " .
                                "Please see Article::editUpdates() for an invocation example.\n" );
                }
                $this->mTitle = $title;
                $this->mId = $title->getArticleID();

                $this->mParserOutput = $parserOutput;
                $this->mLinks = $parserOutput->getLinks();
                $this->mImages = $parserOutput->getImages();
                $this->mTemplates = $parserOutput->getTemplates();
                $this->mExternals = $parserOutput->getExternalLinks();
                $this->mCategories = $parserOutput->getCategories();
                $this->mProperties = $parserOutput->getProperties();
                $this->mInterwikis = $parserOutput->getInterwikiLinks();

                # Convert the format of the interlanguage links
                # I didn't want to change it in the ParserOutput, because that array is passed all
                # the way back to the skin, so either a skin API break would be required, or an
                # inefficient back-conversion.
                $ill = $parserOutput->getLanguageLinks();
                $this->mInterlangs = array();
                foreach ( $ill as $link ) {
                        list( $key, $title ) = explode( ':', $link, 2 );
                        $this->mInterlangs[$key] = $title;
                }

                $this->mRecursive = $recursive;

                wfRunHooks( 'LinksUpdateConstructed', array( &$this ) );
        }

        /**
         * Update link tables with outgoing links from an updated article
         */
        public function doUpdate() {
                global $wgUseDumbLinkUpdate;

                wfRunHooks( 'LinksUpdate', array( &$this ) );
                if ( $wgUseDumbLinkUpdate ) {
                        $this->doDumbUpdate();
                } else {
                        $this->doIncrementalUpdate();
                }
                wfRunHooks( 'LinksUpdateComplete', array( &$this ) );
        }

        protected function doIncrementalUpdate() {
                wfProfileIn( __METHOD__ );

                # Page links
                $existing = $this->getExistingLinks();
                $this->incrTableUpdate( 'pagelinks', 'pl', $this->getLinkDeletions( $existing ),
                        $this->getLinkInsertions( $existing ) );

                # Image links
                $existing = $this->getExistingImages();

                $imageDeletes = $this->getImageDeletions( $existing );
                $this->incrTableUpdate( 'imagelinks', 'il', $imageDeletes, $this->getImageInsertions( $existing ) );

                # Invalidate all image description pages which had links added or removed
                $imageUpdates = $imageDeletes + array_diff_key( $this->mImages, $existing );
                $this->invalidateImageDescriptions( $imageUpdates );

                # External links
                $existing = $this->getExistingExternals();
                $this->incrTableUpdate( 'externallinks', 'el', $this->getExternalDeletions( $existing ),
                $this->getExternalInsertions( $existing ) );

                # Language links
                $existing = $this->getExistingInterlangs();
                $this->incrTableUpdate( 'langlinks', 'll', $this->getInterlangDeletions( $existing ),
                        $this->getInterlangInsertions( $existing ) );

                # Inline interwiki links
                $existing = $this->getExistingInterwikis();
                $this->incrTableUpdate( 'iwlinks', 'iwl', $this->getInterwikiDeletions( $existing ),
                        $this->getInterwikiInsertions( $existing ) );

                # Template links
                $existing = $this->getExistingTemplates();
                $this->incrTableUpdate( 'templatelinks', 'tl', $this->getTemplateDeletions( $existing ),
                        $this->getTemplateInsertions( $existing ) );

                # Category links
                $existing = $this->getExistingCategories();

                $categoryDeletes = $this->getCategoryDeletions( $existing );

                $this->incrTableUpdate( 'categorylinks', 'cl', $categoryDeletes, $this->getCategoryInsertions( $existing ) );

                # Invalidate all categories which were added, deleted or changed (set symmetric difference)
                $categoryInserts = array_diff_assoc( $this->mCategories, $existing );
                $categoryUpdates = $categoryInserts + $categoryDeletes;
                $this->invalidateCategories( $categoryUpdates );
                $this->updateCategoryCounts( $categoryInserts, $categoryDeletes );

                # Page properties
                $existing = $this->getExistingProperties();

                $propertiesDeletes = $this->getPropertyDeletions( $existing );

                $this->incrTableUpdate( 'page_props', 'pp', $propertiesDeletes, $this->getPropertyInsertions( $existing ) );

                # Invalidate the necessary pages
                $changed = $propertiesDeletes + array_diff_assoc( $this->mProperties, $existing );
                $this->invalidateProperties( $changed );

                # Refresh links of all pages including this page
                # This will be in a separate transaction
                if ( $this->mRecursive ) {
                        $this->queueRecursiveJobs();
                }

                wfProfileOut( __METHOD__ );
        }

        /**
         * Link update which clears the previous entries and inserts new ones
         * May be slower or faster depending on level of lock contention and write speed of DB
         * Also useful where link table corruption needs to be repaired, e.g. in refreshLinks.php
         */
        protected function doDumbUpdate() {
                wfProfileIn( __METHOD__ );

                # Refresh category pages and image description pages
                $existing = $this->getExistingCategories();
                $categoryInserts = array_diff_assoc( $this->mCategories, $existing );
                $categoryDeletes = array_diff_assoc( $existing, $this->mCategories );
                $categoryUpdates = $categoryInserts + $categoryDeletes;
                $existing = $this->getExistingImages();
                $imageUpdates = array_diff_key( $existing, $this->mImages ) + array_diff_key( $this->mImages, $existing );

                $this->dumbTableUpdate( 'pagelinks',     $this->getLinkInsertions(),     'pl_from' );
                $this->dumbTableUpdate( 'imagelinks',    $this->getImageInsertions(),    'il_from' );
                $this->dumbTableUpdate( 'categorylinks', $this->getCategoryInsertions(), 'cl_from' );
                $this->dumbTableUpdate( 'templatelinks', $this->getTemplateInsertions(), 'tl_from' );
                $this->dumbTableUpdate( 'externallinks', $this->getExternalInsertions(), 'el_from' );
                $this->dumbTableUpdate( 'langlinks',     $this->getInterlangInsertions(),'ll_from' );
                $this->dumbTableUpdate( 'iwlinks',       $this->getInterwikiInsertions(),'iwl_from' );
                $this->dumbTableUpdate( 'page_props',    $this->getPropertyInsertions(), 'pp_page' );

                # Update the cache of all the category pages and image description
                # pages which were changed, and fix the category table count
                $this->invalidateCategories( $categoryUpdates );
                $this->updateCategoryCounts( $categoryInserts, $categoryDeletes );
                $this->invalidateImageDescriptions( $imageUpdates );

                # Refresh links of all pages including this page
                # This will be in a separate transaction
                if ( $this->mRecursive ) {
                        $this->queueRecursiveJobs();
                }

                wfProfileOut( __METHOD__ );
        }

        function queueRecursiveJobs() {
                global $wgUpdateRowsPerJob;
                wfProfileIn( __METHOD__ );

                $cache = $this->mTitle->getBacklinkCache();
                $batches = $cache->partition( 'templatelinks', $wgUpdateRowsPerJob );
                if ( !$batches ) {
                        wfProfileOut( __METHOD__ );
                        return;
                }
                $jobs = array();
                foreach ( $batches as $batch ) {
                        list( $start, $end ) = $batch;
                        $params = array(
                                'start' => $start,
                                'end' => $end,
                        );
                        $jobs[] = new RefreshLinksJob2( $this->mTitle, $params );
                }
                Job::batchInsert( $jobs );

                wfProfileOut( __METHOD__ );
        }

        /**
         * Invalidate the cache of a list of pages from a single namespace
         *
         * @param $namespace Integer
         * @param $dbkeys Array
         */
        function invalidatePages( $namespace, $dbkeys ) {
                if ( !count( $dbkeys ) ) {
                        return;
                }

                /**
                 * Determine which pages need to be updated
                 * This is necessary to prevent the job queue from smashing the DB with
                 * large numbers of concurrent invalidations of the same page
                 */
                $now = $this->mDb->timestamp();
                $ids = array();
                $res = $this->mDb->select( 'page', array( 'page_id' ),
                        array(
                                'page_namespace' => $namespace,
                                'page_title IN (' . $this->mDb->makeList( $dbkeys ) . ')',
                                'page_touched < ' . $this->mDb->addQuotes( $now )
                        ), __METHOD__
                );
                foreach ( $res as $row ) {
                        $ids[] = $row->page_id;
                }
                if ( !count( $ids ) ) {
                        return;
                }

                /**
                 * Do the update
                 * We still need the page_touched condition, in case the row has changed since
                 * the non-locking select above.
                 */
                $this->mDb->update( 'page', array( 'page_touched' => $now ),
                        array(
                                'page_id IN (' . $this->mDb->makeList( $ids ) . ')',
                                'page_touched < ' . $this->mDb->addQuotes( $now )
                        ), __METHOD__
                );
        }

        function invalidateCategories( $cats ) {
                $this->invalidatePages( NS_CATEGORY, array_keys( $cats ) );
        }

        /**
         * Update all the appropriate counts in the category table.
         * @param $added associative array of category name => sort key
         * @param $deleted associative array of category name => sort key
         */
        function updateCategoryCounts( $added, $deleted ) {
                $a = new Article($this->mTitle);
                $a->updateCategoryCounts(
                        array_keys( $added ), array_keys( $deleted )
                );
        }

        function invalidateImageDescriptions( $images ) {
                $this->invalidatePages( NS_FILE, array_keys( $images ) );
        }

        function dumbTableUpdate( $table, $insertions, $fromField ) {
                $this->mDb->delete( $table, array( $fromField => $this->mId ), __METHOD__ );
                if ( count( $insertions ) ) {
                        # The link array was constructed without FOR UPDATE, so there may
                        # be collisions.  This may cause minor link table inconsistencies,
                        # which is better than crippling the site with lock contention.
                        $this->mDb->insert( $table, $insertions, __METHOD__, array( 'IGNORE' ) );
                }
        }

        /**
         * Update a table by doing a delete query then an insert query
         * @private
         */
        function incrTableUpdate( $table, $prefix, $deletions, $insertions ) {
                if ( $table == 'page_props' ) {
                        $fromField = 'pp_page';
                } else {
                        $fromField = "{$prefix}_from";
                }
                $where = array( $fromField => $this->mId );
                if ( $table == 'pagelinks' || $table == 'templatelinks' || $table == 'iwlinks' ) {
                        if ( $table == 'iwlinks' ) {
                                $baseKey = 'iwl_prefix';
                        } else {
                                $baseKey = "{$prefix}_namespace";
                        }
                        $clause = $this->mDb->makeWhereFrom2d( $deletions, $baseKey, "{$prefix}_title" );
                        if ( $clause ) {
                                $where[] = $clause;
                        } else {
                                $where = false;
                        }
                } else {
                        if ( $table == 'langlinks' ) {
                                $toField = 'll_lang';
                        } elseif ( $table == 'page_props' ) {
                                $toField = 'pp_propname';
                        } else {
                                $toField = $prefix . '_to';
                        }
                        if ( count( $deletions ) ) {
                                $where[] = "$toField IN (" . $this->mDb->makeList( array_keys( $deletions ) ) . ')';
                        } else {
                                $where = false;
                        }
                }
                if ( $where ) {
                        $this->mDb->delete( $table, $where, __METHOD__ );
                }
                if ( count( $insertions ) ) {
                        $this->mDb->insert( $table, $insertions, __METHOD__, 'IGNORE' );
                }
        }


        /**
         * Get an array of pagelinks insertions for passing to the DB
         * Skips the titles specified by the 2-D array $existing
         * @private
         */
        function getLinkInsertions( $existing = array() ) {
                $arr = array();
                foreach( $this->mLinks as $ns => $dbkeys ) {
                        $diffs = isset( $existing[$ns] ) ? array_diff_key( $dbkeys, $existing[$ns] ) : $dbkeys;
                        foreach ( $diffs as $dbk => $id ) {
                                $arr[] = array(
                                        'pl_from'      => $this->mId,
                                        'pl_namespace' => $ns,
                                        'pl_title'     => $dbk
                                );
                        }
                }
                return $arr;
        }

        /**
         * Get an array of template insertions. Like getLinkInsertions()
         * @private
         */
        function getTemplateInsertions( $existing = array() ) {
                $arr = array();
                foreach( $this->mTemplates as $ns => $dbkeys ) {
                        $diffs = isset( $existing[$ns] ) ? array_diff_key( $dbkeys, $existing[$ns] ) : $dbkeys;
                        foreach ( $diffs as $dbk => $id ) {
                                $arr[] = array(
                                        'tl_from'      => $this->mId,
                                        'tl_namespace' => $ns,
                                        'tl_title'     => $dbk
                                );
                        }
                }
                return $arr;
        }

        /**
         * Get an array of image insertions
         * Skips the names specified in $existing
         * @private
         */
        function getImageInsertions( $existing = array() ) {
                $arr = array();
                $diffs = array_diff_key( $this->mImages, $existing );
                foreach( $diffs as $iname => $dummy ) {
                        $arr[] = array(
                                'il_from' => $this->mId,
                                'il_to'   => $iname
                        );
                }
                return $arr;
        }

        /**
         * Get an array of externallinks insertions. Skips the names specified in $existing
         * @private
         */
        function getExternalInsertions( $existing = array() ) {
                $arr = array();
                $diffs = array_diff_key( $this->mExternals, $existing );
                foreach( $diffs as $url => $dummy ) {
                        $arr[] = array(
                                'el_from'   => $this->mId,
                                'el_to'     => $url,
                                'el_index'  => wfMakeUrlIndex( $url ),
                        );
                }
                return $arr;
        }

        /**
         * Get an array of category insertions
         *
         * @param $existing Array mapping existing category names to sort keys. If both
         * match a link in $this, the link will be omitted from the output
         * @private
         */
        function getCategoryInsertions( $existing = array() ) {
                global $wgContLang, $wgCategoryCollation;
                $diffs = array_diff_assoc( $this->mCategories, $existing );
                $arr = array();
                foreach ( $diffs as $name => $sortkey ) {
                        $nt = Title::makeTitleSafe( NS_CATEGORY, $name );
                        $wgContLang->findVariantLink( $name, $nt, true );

                        if ( $this->mTitle->getNamespace() == NS_CATEGORY ) {
                                $type = 'subcat';
                        } elseif ( $this->mTitle->getNamespace() == NS_FILE ) {
                                $type = 'file';
                        } else {
                                $type = 'page';
                        }

                        # TODO: This is kind of wrong, because someone might set a sort
                        # key prefix that's the same as the default sortkey for the
                        # title.  This should be fixed by refactoring code to replace
                        # $sortkey in this array by a prefix, but it's basically harmless
                        # (Title::moveTo() has had the same issue for a long time).
                        if ( $this->mTitle->getCategorySortkey() == $sortkey ) {
                                $prefix = '';
                                $sortkey = $wgContLang->convertToSortkey( $sortkey );
                        } else {
                                # Treat custom sortkeys as a prefix, so that if multiple
                                # things are forced to sort as '*' or something, they'll
                                # sort properly in the category rather than in page_id
                                # order or such.
                                $prefix = $sortkey;
                                $sortkey = $wgContLang->convertToSortkey(
                                        $this->mTitle->getCategorySortkey( $prefix ) );
                        }

                        $arr[] = array(
                                'cl_from'    => $this->mId,
                                'cl_to'      => $name,
                                'cl_sortkey' => $sortkey,
                                'cl_timestamp' => $this->mDb->timestamp(),
                                'cl_sortkey_prefix' => $prefix,
                                'cl_collation' => $wgCategoryCollation,
                                'cl_type' => $type,
                        );
                }
                return $arr;
        }

        /**
         * Get an array of interlanguage link insertions
         *
         * @param $existing Array mapping existing language codes to titles
         * @private
         */
        function getInterlangInsertions( $existing = array() ) {
            $diffs = array_diff_assoc( $this->mInterlangs, $existing );
            $arr = array();
            foreach( $diffs as $lang => $title ) {
                $arr[] = array(
                    'll_from'  => $this->mId,
                    'll_lang'  => $lang,
                    'll_title' => $title
                );
            }
            return $arr;
        }

        /**
         * Get an array of page property insertions
         */
        function getPropertyInsertions( $existing = array() ) {
                $diffs = array_diff_assoc( $this->mProperties, $existing );
                $arr = array();
                foreach ( $diffs as $name => $value ) {
                        $arr[] = array(
                                'pp_page'      => $this->mId,
                                'pp_propname'  => $name,
                                'pp_value'     => $value,
                        );
                }
                return $arr;
        }

        /**
         * Get an array of interwiki insertions for passing to the DB
         * Skips the titles specified by the 2-D array $existing
         * @private
         */
        function getInterwikiInsertions( $existing = array() ) {
                $arr = array();
                foreach( $this->mInterwikis as $prefix => $dbkeys ) {
                        $diffs = isset( $existing[$prefix] ) ? array_diff_key( $dbkeys, $existing[$prefix] ) : $dbkeys;
                        foreach ( $diffs as $dbk => $id ) {
                                $arr[] = array(
                                        'iwl_from'   => $this->mId,
                                        'iwl_prefix' => $prefix,
                                        'iwl_title'  => $dbk
                                );
                        }
                }
                return $arr;
        }

        /**
         * Given an array of existing links, returns those links which are not in $this
         * and thus should be deleted.
         * @private
         */
        function getLinkDeletions( $existing ) {
                $del = array();
                foreach ( $existing as $ns => $dbkeys ) {
                        if ( isset( $this->mLinks[$ns] ) ) {
                                $del[$ns] = array_diff_key( $existing[$ns], $this->mLinks[$ns] );
                        } else {
                                $del[$ns] = $existing[$ns];
                        }
                }
                return $del;
        }

        /**
         * Given an array of existing templates, returns those templates which are not in $this
         * and thus should be deleted.
         * @private
         */
        function getTemplateDeletions( $existing ) {
                $del = array();
                foreach ( $existing as $ns => $dbkeys ) {
                        if ( isset( $this->mTemplates[$ns] ) ) {
                                $del[$ns] = array_diff_key( $existing[$ns], $this->mTemplates[$ns] );
                        } else {
                                $del[$ns] = $existing[$ns];
                        }
                }
                return $del;
        }

        /**
         * Given an array of existing images, returns those images which are not in $this
         * and thus should be deleted.
         * @private
         */
        function getImageDeletions( $existing ) {
                return array_diff_key( $existing, $this->mImages );
        }

        /**
         * Given an array of existing external links, returns those links which are not
         * in $this and thus should be deleted.
         * @private
         */
        function getExternalDeletions( $existing ) {
                return array_diff_key( $existing, $this->mExternals );
        }

        /**
         * Given an array of existing categories, returns those categories which are not in $this
         * and thus should be deleted.
         * @private
         */
        function getCategoryDeletions( $existing ) {
                return array_diff_assoc( $existing, $this->mCategories );
        }

        /**
         * Given an array of existing interlanguage links, returns those links which are not
         * in $this and thus should be deleted.
         * @private
         */
        function getInterlangDeletions( $existing ) {
            return array_diff_assoc( $existing, $this->mInterlangs );
        }

        /**
         * Get array of properties which should be deleted.
         * @private
         */
        function getPropertyDeletions( $existing ) {
                return array_diff_assoc( $existing, $this->mProperties );
        }

        /**
         * Given an array of existing interwiki links, returns those links which are not in $this
         * and thus should be deleted.
         * @private
         */
        function getInterwikiDeletions( $existing ) {
                $del = array();
                foreach ( $existing as $prefix => $dbkeys ) {
                        if ( isset( $this->mInterwikis[$prefix] ) ) {
                                $del[$prefix] = array_diff_key( $existing[$prefix], $this->mInterwikis[$prefix] );
                        } else {
                                $del[$prefix] = $existing[$prefix];
                        }
                }
                return $del;
        }

        /**
         * Get an array of existing links, as a 2-D array
         * @private
         */
        function getExistingLinks() {
                $res = $this->mDb->select( 'pagelinks', array( 'pl_namespace', 'pl_title' ),
                        array( 'pl_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        if ( !isset( $arr[$row->pl_namespace] ) ) {
                                $arr[$row->pl_namespace] = array();
                        }
                        $arr[$row->pl_namespace][$row->pl_title] = 1;
                }
                return $arr;
        }

        /**
         * Get an array of existing templates, as a 2-D array
         * @private
         */
        function getExistingTemplates() {
                $res = $this->mDb->select( 'templatelinks', array( 'tl_namespace', 'tl_title' ),
                        array( 'tl_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        if ( !isset( $arr[$row->tl_namespace] ) ) {
                                $arr[$row->tl_namespace] = array();
                        }
                        $arr[$row->tl_namespace][$row->tl_title] = 1;
                }
                return $arr;
        }

        /**
         * Get an array of existing images, image names in the keys
         * @private
         */
        function getExistingImages() {
                $res = $this->mDb->select( 'imagelinks', array( 'il_to' ),
                        array( 'il_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        $arr[$row->il_to] = 1;
                }
                return $arr;
        }

        /**
         * Get an array of existing external links, URLs in the keys
         * @private
         */
        function getExistingExternals() {
                $res = $this->mDb->select( 'externallinks', array( 'el_to' ),
                        array( 'el_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        $arr[$row->el_to] = 1;
                }
                return $arr;
        }

        /**
         * Get an array of existing categories, with the name in the key and sort key in the value.
         * @private
         */
        function getExistingCategories() {
                $res = $this->mDb->select( 'categorylinks', array( 'cl_to', 'cl_sortkey' ),
                        array( 'cl_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        $arr[$row->cl_to] = $row->cl_sortkey;
                }
                return $arr;
        }

        /**
         * Get an array of existing interlanguage links, with the language code in the key and the
         * title in the value.
         * @private
         */
        function getExistingInterlangs() {
                $res = $this->mDb->select( 'langlinks', array( 'll_lang', 'll_title' ),
                        array( 'll_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        $arr[$row->ll_lang] = $row->ll_title;
                }
                return $arr;
        }

        /**
         * Get an array of existing inline interwiki links, as a 2-D array
         * @return array (prefix => array(dbkey => 1))
         */
        protected function getExistingInterwikis() {
                $res = $this->mDb->select( 'iwlinks', array( 'iwl_prefix', 'iwl_title' ),
                        array( 'iwl_from' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        if ( !isset( $arr[$row->iwl_prefix] ) ) {
                                $arr[$row->iwl_prefix] = array();
                        }
                        $arr[$row->iwl_prefix][$row->iwl_title] = 1;
                }
                return $arr;
        }

        /**
         * Get an array of existing categories, with the name in the key and sort key in the value.
         * @private
         */
        function getExistingProperties() {
                $res = $this->mDb->select( 'page_props', array( 'pp_propname', 'pp_value' ),
                        array( 'pp_page' => $this->mId ), __METHOD__, $this->mOptions );
                $arr = array();
                foreach ( $res as $row ) {
                        $arr[$row->pp_propname] = $row->pp_value;
                }
                return $arr;
        }


        /**
         * Return the title object of the page being updated
         */
        function getTitle() {
                return $this->mTitle;
        }
        
        /**
         * Return the list of images used as generated by the parser
         */
        public function getImages() {
                return $this->mImages;
        }

        /**
         * Invalidate any necessary link lists related to page property changes
         */
        function invalidateProperties( $changed ) {
                global $wgPagePropLinkInvalidations;

                foreach ( $changed as $name => $value ) {
                        if ( isset( $wgPagePropLinkInvalidations[$name] ) ) {
                                $inv = $wgPagePropLinkInvalidations[$name];
                                if ( !is_array( $inv ) ) {
                                        $inv = array( $inv );
                                }
                                foreach ( $inv as $table ) {
                                        $update = new HTMLCacheUpdate( $this->mTitle, $table );
                                        $update->doUpdate();
                                }
                        }
                }
        }
}