rdbms: Avoid selectDB() call in LoadMonitor new connections

[mediawiki.git] / includes / Category.php

<?php
/**
 * Representation for a category.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @author Simetrical
 */

/**
 * Category objects are immutable, strictly speaking. If you call methods that change the database,
 * like to refresh link counts, the objects will be appropriately reinitialized.
 * Member variables are lazy-initialized.
 *
 * @todo Move some stuff from CategoryPage.php to here, and use that.
 */
class Category {
        /** Name of the category, normalized to DB-key form */
        private $mName = null;
        private $mID = null;
        /**
         * Category page title
         * @var Title
         */
        private $mTitle = null;
        /** Counts of membership (cat_pages, cat_subcats, cat_files) */
        private $mPages = null, $mSubcats = null, $mFiles = null;

        const LOAD_ONLY = 0;
        const LAZY_INIT_ROW = 1;

        private function __construct() {
        }

        /**
         * Set up all member variables using a database query.
         * @param integer $mode
         * @throws MWException
         * @return bool True on success, false on failure.
         */
        protected function initialize( $mode = self::LOAD_ONLY ) {
                if ( $this->mName === null && $this->mID === null ) {
                        throw new MWException( __METHOD__ . ' has both names and IDs null' );
                } elseif ( $this->mID === null ) {
                        $where = [ 'cat_title' => $this->mName ];
                } elseif ( $this->mName === null ) {
                        $where = [ 'cat_id' => $this->mID ];
                } else {
                        # Already initialized
                        return true;
                }

                $dbr = wfGetDB( DB_REPLICA );
                $row = $dbr->selectRow(
                        'category',
                        [ 'cat_id', 'cat_title', 'cat_pages', 'cat_subcats', 'cat_files' ],
                        $where,
                        __METHOD__
                );

                if ( !$row ) {
                        # Okay, there were no contents.  Nothing to initialize.
                        if ( $this->mTitle ) {
                                # If there is a title object but no record in the category table,
                                # treat this as an empty category.
                                $this->mID = false;
                                $this->mName = $this->mTitle->getDBkey();
                                $this->mPages = 0;
                                $this->mSubcats = 0;
                                $this->mFiles = 0;

                                # If the title exists, call refreshCounts to add a row for it.
                                if ( $mode === self::LAZY_INIT_ROW && $this->mTitle->exists() ) {
                                        DeferredUpdates::addCallableUpdate( [ $this, 'refreshCounts' ] );
                                }

                                return true;
                        } else {
                                return false; # Fail
                        }
                }

                $this->mID = $row->cat_id;
                $this->mName = $row->cat_title;
                $this->mPages = $row->cat_pages;
                $this->mSubcats = $row->cat_subcats;
                $this->mFiles = $row->cat_files;

                # (T15683) If the count is negative, then 1) it's obviously wrong
                # and should not be kept, and 2) we *probably* don't have to scan many
                # rows to obtain the correct figure, so let's risk a one-time recount.
                if ( $this->mPages < 0 || $this->mSubcats < 0 || $this->mFiles < 0 ) {
                        $this->mPages = max( $this->mPages, 0 );
                        $this->mSubcats = max( $this->mSubcats, 0 );
                        $this->mFiles = max( $this->mFiles, 0 );

                        if ( $mode === self::LAZY_INIT_ROW ) {
                                DeferredUpdates::addCallableUpdate( [ $this, 'refreshCounts' ] );
                        }
                }

                return true;
        }

        /**
         * Factory function.
         *
         * @param array $name A category name (no "Category:" prefix).  It need
         *   not be normalized, with spaces replaced by underscores.
         * @return mixed Category, or false on a totally invalid name
         */
        public static function newFromName( $name ) {
                $cat = new self();
                $title = Title::makeTitleSafe( NS_CATEGORY, $name );

                if ( !is_object( $title ) ) {
                        return false;
                }

                $cat->mTitle = $title;
                $cat->mName = $title->getDBkey();

                return $cat;
        }

        /**
         * Factory function.
         *
         * @param Title $title Title for the category page
         * @return Category|bool On a totally invalid name
         */
        public static function newFromTitle( $title ) {
                $cat = new self();

                $cat->mTitle = $title;
                $cat->mName = $title->getDBkey();

                return $cat;
        }

        /**
         * Factory function.
         *
         * @param int $id A category id
         * @return Category
         */
        public static function newFromID( $id ) {
                $cat = new self();
                $cat->mID = intval( $id );
                return $cat;
        }

        /**
         * Factory function, for constructing a Category object from a result set
         *
         * @param object $row Result set row, must contain the cat_xxx fields. If the
         *   fields are null, the resulting Category object will represent an empty
         *   category if a title object was given. If the fields are null and no
         *   title was given, this method fails and returns false.
         * @param Title $title Optional title object for the category represented by
         *   the given row. May be provided if it is already known, to avoid having
         *   to re-create a title object later.
         * @return Category|false
         */
        public static function newFromRow( $row, $title = null ) {
                $cat = new self();
                $cat->mTitle = $title;

                # NOTE: the row often results from a LEFT JOIN on categorylinks. This may result in
                #       all the cat_xxx fields being null, if the category page exists, but nothing
                #       was ever added to the category. This case should be treated link an empty
                #       category, if possible.

                if ( $row->cat_title === null ) {
                        if ( $title === null ) {
                                # the name is probably somewhere in the row, for example as page_title,
                                # but we can't know that here...
                                return false;
                        } else {
                                # if we have a title object, fetch the category name from there
                                $cat->mName = $title->getDBkey();
                        }

                        $cat->mID = false;
                        $cat->mSubcats = 0;
                        $cat->mPages = 0;
                        $cat->mFiles = 0;
                } else {
                        $cat->mName = $row->cat_title;
                        $cat->mID = $row->cat_id;
                        $cat->mSubcats = $row->cat_subcats;
                        $cat->mPages = $row->cat_pages;
                        $cat->mFiles = $row->cat_files;
                }

                return $cat;
        }

        /**
         * @return mixed DB key name, or false on failure
         */
        public function getName() {
                return $this->getX( 'mName' );
        }

        /**
         * @return mixed Category ID, or false on failure
         */
        public function getID() {
                return $this->getX( 'mID' );
        }

        /**
         * @return mixed Total number of member pages, or false on failure
         */
        public function getPageCount() {
                return $this->getX( 'mPages' );
        }

        /**
         * @return mixed Number of subcategories, or false on failure
         */
        public function getSubcatCount() {
                return $this->getX( 'mSubcats' );
        }

        /**
         * @return mixed Number of member files, or false on failure
         */
        public function getFileCount() {
                return $this->getX( 'mFiles' );
        }

        /**
         * @return Title|bool Title for this category, or false on failure.
         */
        public function getTitle() {
                if ( $this->mTitle ) {
                        return $this->mTitle;
                }

                if ( !$this->initialize( self::LAZY_INIT_ROW ) ) {
                        return false;
                }

                $this->mTitle = Title::makeTitleSafe( NS_CATEGORY, $this->mName );
                return $this->mTitle;
        }

        /**
         * Fetch a TitleArray of up to $limit category members, beginning after the
         * category sort key $offset.
         * @param int|bool $limit
         * @param string $offset
         * @return TitleArray TitleArray object for category members.
         */
        public function getMembers( $limit = false, $offset = '' ) {
                $dbr = wfGetDB( DB_REPLICA );

                $conds = [ 'cl_to' => $this->getName(), 'cl_from = page_id' ];
                $options = [ 'ORDER BY' => 'cl_sortkey' ];

                if ( $limit ) {
                        $options['LIMIT'] = $limit;
                }

                if ( $offset !== '' ) {
                        $conds[] = 'cl_sortkey > ' . $dbr->addQuotes( $offset );
                }

                $result = TitleArray::newFromResult(
                        $dbr->select(
                                [ 'page', 'categorylinks' ],
                                [ 'page_id', 'page_namespace', 'page_title', 'page_len',
                                        'page_is_redirect', 'page_latest' ],
                                $conds,
                                __METHOD__,
                                $options
                        )
                );

                return $result;
        }

        /**
         * Generic accessor
         * @param string $key
         * @return bool
         */
        private function getX( $key ) {
                if ( !$this->initialize( self::LAZY_INIT_ROW ) ) {
                        return false;
                }
                return $this->{$key};
        }

        /**
         * Refresh the counts for this category.
         *
         * @return bool True on success, false on failure
         */
        public function refreshCounts() {
                if ( wfReadOnly() ) {
                        return false;
                }

                # If we have just a category name, find out whether there is an
                # existing row. Or if we have just an ID, get the name, because
                # that's what categorylinks uses.
                if ( !$this->initialize( self::LOAD_ONLY ) ) {
                        return false;
                }

                $dbw = wfGetDB( DB_MASTER );
                # Avoid excess contention on the same category (T162121)
                $name = __METHOD__ . ':' . md5( $this->mName );
                $scopedLock = $dbw->getScopedLockAndFlush( $name, __METHOD__, 1 );
                if ( !$scopedLock ) {
                        return false;
                }

                $dbw->startAtomic( __METHOD__ );

                $cond1 = $dbw->conditional( [ 'page_namespace' => NS_CATEGORY ], 1, 'NULL' );
                $cond2 = $dbw->conditional( [ 'page_namespace' => NS_FILE ], 1, 'NULL' );
                $result = $dbw->selectRow(
                        [ 'categorylinks', 'page' ],
                        [ 'pages' => 'COUNT(*)',
                                'subcats' => "COUNT($cond1)",
                                'files' => "COUNT($cond2)"
                        ],
                        [ 'cl_to' => $this->mName, 'page_id = cl_from' ],
                        __METHOD__,
                        [ 'LOCK IN SHARE MODE' ]
                );

                $shouldExist = $result->pages > 0 || $this->getTitle()->exists();

                if ( $this->mID ) {
                        if ( $shouldExist ) {
                                # The category row already exists, so do a plain UPDATE instead
                                # of INSERT...ON DUPLICATE KEY UPDATE to avoid creating a gap
                                # in the cat_id sequence. The row may or may not be "affected".
                                $dbw->update(
                                        'category',
                                        [
                                                'cat_pages' => $result->pages,
                                                'cat_subcats' => $result->subcats,
                                                'cat_files' => $result->files
                                        ],
                                        [ 'cat_title' => $this->mName ],
                                        __METHOD__
                                );
                        } else {
                                # The category is empty and has no description page, delete it
                                $dbw->delete(
                                        'category',
                                        [ 'cat_title' => $this->mName ],
                                        __METHOD__
                                );
                                $this->mID = false;
                        }
                } elseif ( $shouldExist ) {
                        # The category row doesn't exist but should, so create it. Use
                        # upsert in case of races.
                        $dbw->upsert(
                                'category',
                                [
                                        'cat_title' => $this->mName,
                                        'cat_pages' => $result->pages,
                                        'cat_subcats' => $result->subcats,
                                        'cat_files' => $result->files
                                ],
                                [ 'cat_title' ],
                                [
                                        'cat_pages' => $result->pages,
                                        'cat_subcats' => $result->subcats,
                                        'cat_files' => $result->files
                                ],
                                __METHOD__
                        );
                        // @todo: Should we update $this->mID here? Or not since Category
                        // objects tend to be short lived enough to not matter?
                }

                $dbw->endAtomic( __METHOD__ );

                # Now we should update our local counts.
                $this->mPages = $result->pages;
                $this->mSubcats = $result->subcats;
                $this->mFiles = $result->files;

                return true;
        }
}