includes/pager/IndexPager.php

   1 <?php
   2 /**
   3  * Efficient paging for SQL queries.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Pager
  22  */
  23
  24 use Wikimedia\Rdbms\IResultWrapper;
  25 use Wikimedia\Rdbms\IDatabase;
  26
  27 /**
  28  * IndexPager is an efficient pager which uses a (roughly unique) index in the
  29  * data set to implement paging, rather than a "LIMIT offset,limit" clause.
  30  * In MySQL, such a limit/offset clause requires counting through the
  31  * specified number of offset rows to find the desired data, which can be
  32  * expensive for large offsets.
  33  *
  34  * ReverseChronologicalPager is a child class of the abstract IndexPager, and
  35  * contains  some formatting and display code which is specific to the use of
  36  * timestamps as  indexes. Here is a synopsis of its operation:
  37  *
  38  *    * The query is specified by the offset, limit and direction (dir)
  39  *      parameters, in addition to any subclass-specific parameters.
  40  *    * The offset is the non-inclusive start of the DB query. A row with an
  41  *      index value equal to the offset will never be shown.
  42  *    * The query may either be done backwards, where the rows are returned by
  43  *      the database in the opposite order to which they are displayed to the
  44  *      user, or forwards. This is specified by the "dir" parameter, dir=prev
  45  *      means backwards, anything else means forwards. The offset value
  46  *      specifies the start of the database result set, which may be either
  47  *      the start or end of the displayed data set. This allows "previous"
  48  *      links to be implemented without knowledge of the index value at the
  49  *      start of the previous page.
  50  *    * An additional row beyond the user-specified limit is always requested.
  51  *      This allows us to tell whether we should display a "next" link in the
  52  *      case of forwards mode, or a "previous" link in the case of backwards
  53  *      mode. Determining whether to display the other link (the one for the
  54  *      page before the start of the database result set) can be done
  55  *      heuristically by examining the offset.
  56  *
  57  *    * An empty offset indicates that the offset condition should be omitted
  58  *      from the query. This naturally produces either the first page or the
  59  *      last page depending on the dir parameter.
  60  *
  61  *  Subclassing the pager to implement concrete functionality should be fairly
  62  *  simple, please see the examples in HistoryAction.php and
  63  *  SpecialBlockList.php. You just need to override formatRow(),
  64  *  getQueryInfo() and getIndexField(). Don't forget to call the parent
  65  *  constructor if you override it.
  66  *
  67  * @ingroup Pager
  68  */
  69 abstract class IndexPager extends ContextSource implements Pager {
  70         /**
  71          * Constants for the $mDefaultDirection field.
  72          *
  73          * These are boolean for historical reasons and should stay boolean for backwards-compatibility.
  74          */
  75         const DIR_ASCENDING = false;
  76         const DIR_DESCENDING = true;
  77
  78         /** @var WebRequest */
  79         public $mRequest;
  80         /** @var int[] List of default entry limit options to be presented to clients */
  81         public $mLimitsShown = [ 20, 50, 100, 250, 500 ];
  82         /** @var int The default entry limit choosen for clients */
  83         public $mDefaultLimit = 50;
  84         /** @var mixed The starting point to enumerate entries */
  85         public $mOffset;
  86         /** @var int The maximum number of entries to show */
  87         public $mLimit;
  88         /** @var bool Whether the listing query completed */
  89         public $mQueryDone = false;
  90         /** @var IDatabase */
  91         public $mDb;
  92         /** @var stdClass|bool|null Extra row fetched at the end to see if the end was reached */
  93         public $mPastTheEndRow;
  94
  95         /**
  96          * The index to actually be used for ordering. This is a single column,
  97          * for one ordering, even if multiple orderings are supported.
  98          * @var string
  99          */
 100         protected $mIndexField;
 101         /**
 102          * An array of secondary columns to order by. These fields are not part of the offset.
 103          * This is a column list for one ordering, even if multiple orderings are supported.
 104          * @var string[]
 105          */
 106         protected $mExtraSortFields;
 107         /** For pages that support multiple types of ordering, which one to use.
 108          * @var string|null
 109          */
 110         protected $mOrderType;
 111         /**
 112          * $mDefaultDirection gives the direction to use when sorting results:
 113          * DIR_ASCENDING or DIR_DESCENDING. If $mIsBackwards is set, we start from
 114          * the opposite end, but we still sort the page itself according to
 115          * $mDefaultDirection. For example, if $mDefaultDirection is DIR_ASCENDING
 116          * but we're going backwards, we'll display the last page of results, but
 117          * the last result will be at the bottom, not the top.
 118          *
 119          * Like $mIndexField, $mDefaultDirection will be a single value even if the
 120          * class supports multiple default directions for different order types.
 121          * @var bool
 122          */
 123         public $mDefaultDirection;
 124         /** @var bool */
 125         public $mIsBackwards;
 126
 127         /** @var bool True if the current result set is the first one */
 128         public $mIsFirst;
 129         /** @var bool */
 130         public $mIsLast;
 131
 132         /** @var mixed */
 133         protected $mLastShown;
 134         /** @var mixed */
 135         protected $mFirstShown;
 136         /** @var mixed */
 137         protected $mPastTheEndIndex;
 138         /** @var array */
 139         protected $mDefaultQuery;
 140         /** @var string */
 141         protected $mNavigationBar;
 142
 143         /**
 144          * Whether to include the offset in the query
 145          * @var bool
 146          */
 147         protected $mIncludeOffset = false;
 148
 149         /**
 150          * Result object for the query. Warning: seek before use.
 151          *
 152          * @var IResultWrapper
 153          */
 154         public $mResult;
 155
 156         public function __construct( IContextSource $context = null ) {
 157                 if ( $context ) {
 158                         $this->setContext( $context );
 159                 }
 160
 161                 $this->mRequest = $this->getRequest();
 162
 163                 # NB: the offset is quoted, not validated. It is treated as an
 164                 # arbitrary string to support the widest variety of index types. Be
 165                 # careful outputting it into HTML!
 166                 $this->mOffset = $this->mRequest->getText( 'offset' );
 167
 168                 # Use consistent behavior for the limit options
 169                 $this->mDefaultLimit = $this->getUser()->getIntOption( 'rclimit' );
 170                 if ( !$this->mLimit ) {
 171                         // Don't override if a subclass calls $this->setLimit() in its constructor.
 172                         list( $this->mLimit, /* $offset */ ) = $this->mRequest->getLimitOffset();
 173                 }
 174
 175                 $this->mIsBackwards = ( $this->mRequest->getVal( 'dir' ) == 'prev' );
 176                 # Let the subclass set the DB here; otherwise use a replica DB for the current wiki
 177                 $this->mDb = $this->mDb ?: wfGetDB( DB_REPLICA );
 178
 179                 $index = $this->getIndexField(); // column to sort on
 180                 $extraSort = $this->getExtraSortFields(); // extra columns to sort on for query planning
 181                 $order = $this->mRequest->getVal( 'order' );
 182                 if ( is_array( $index ) && isset( $index[$order] ) ) {
 183                         $this->mOrderType = $order;
 184                         $this->mIndexField = $index[$order];
 185                         $this->mExtraSortFields = isset( $extraSort[$order] )
 186                                 ? (array)$extraSort[$order]
 187                                 : [];
 188                 } elseif ( is_array( $index ) ) {
 189                         # First element is the default
 190                         $this->mIndexField = reset( $index );
 191                         $this->mOrderType = key( $index );
 192                         $this->mExtraSortFields = isset( $extraSort[$this->mOrderType] )
 193                                 ? (array)$extraSort[$this->mOrderType]
 194                                 : [];
 195                 } else {
 196                         # $index is not an array
 197                         $this->mOrderType = null;
 198                         $this->mIndexField = $index;
 199                         $this->mExtraSortFields = (array)$extraSort;
 200                 }
 201
 202                 if ( !isset( $this->mDefaultDirection ) ) {
 203                         $dir = $this->getDefaultDirections();
 204                         $this->mDefaultDirection = is_array( $dir )
 205                                 ? $dir[$this->mOrderType]
 206                                 : $dir;
 207                 }
 208         }
 209
 210         /**
 211          * Get the Database object in use
 212          *
 213          * @return IDatabase
 214          */
 215         public function getDatabase() {
 216                 return $this->mDb;
 217         }
 218
 219         /**
 220          * Do the query, using information from the object context. This function
 221          * has been kept minimal to make it overridable if necessary, to allow for
 222          * result sets formed from multiple DB queries.
 223          */
 224         public function doQuery() {
 225                 # Use the child class name for profiling
 226                 $fname = __METHOD__ . ' (' . static::class . ')';
 227                 $section = Profiler::instance()->scopedProfileIn( $fname );
 228
 229                 $descending = $this->mIsBackwards
 230                         ? ( $this->mDefaultDirection === self::DIR_DESCENDING )
 231                         : ( $this->mDefaultDirection === self::DIR_ASCENDING );
 232
 233                 # Plus an extra row so that we can tell the "next" link should be shown
 234                 $queryLimit = $this->mLimit + 1;
 235
 236                 if ( $this->mOffset == '' ) {
 237                         $isFirst = true;
 238                 } else {
 239                         // If there's an offset, we may or may not be at the first entry.
 240                         // The only way to tell is to run the query in the opposite
 241                         // direction see if we get a row.
 242                         $oldIncludeOffset = $this->mIncludeOffset;
 243                         $this->mIncludeOffset = !$this->mIncludeOffset;
 244                         $isFirst = !$this->reallyDoQuery( $this->mOffset, 1, !$descending )->numRows();
 245                         $this->mIncludeOffset = $oldIncludeOffset;
 246                 }
 247
 248                 $this->mResult = $this->reallyDoQuery(
 249                         $this->mOffset,
 250                         $queryLimit,
 251                         $descending
 252                 );
 253
 254                 $this->extractResultInfo( $isFirst, $queryLimit, $this->mResult );
 255                 $this->mQueryDone = true;
 256
 257                 $this->preprocessResults( $this->mResult );
 258                 $this->mResult->rewind(); // Paranoia
 259         }
 260
 261         /**
 262          * @return IResultWrapper The result wrapper.
 263          */
 264         function getResult() {
 265                 return $this->mResult;
 266         }
 267
 268         /**
 269          * Set the offset from an other source than the request
 270          *
 271          * @param int|string $offset
 272          */
 273         function setOffset( $offset ) {
 274                 $this->mOffset = $offset;
 275         }
 276
 277         /**
 278          * Set the limit from an other source than the request
 279          *
 280          * Verifies limit is between 1 and 5000
 281          *
 282          * @param int|string $limit
 283          */
 284         function setLimit( $limit ) {
 285                 $limit = (int)$limit;
 286                 // WebRequest::getLimitOffset() puts a cap of 5000, so do same here.
 287                 if ( $limit > 5000 ) {
 288                         $limit = 5000;
 289                 }
 290                 if ( $limit > 0 ) {
 291                         $this->mLimit = $limit;
 292                 }
 293         }
 294
 295         /**
 296          * Get the current limit
 297          *
 298          * @return int
 299          */
 300         function getLimit() {
 301                 return $this->mLimit;
 302         }
 303
 304         /**
 305          * Set whether a row matching exactly the offset should be also included
 306          * in the result or not. By default this is not the case, but when the
 307          * offset is user-supplied this might be wanted.
 308          *
 309          * @param bool $include
 310          */
 311         public function setIncludeOffset( $include ) {
 312                 $this->mIncludeOffset = $include;
 313         }
 314
 315         /**
 316          * Extract some useful data from the result object for use by
 317          * the navigation bar, put it into $this
 318          *
 319          * @param bool $isFirst False if there are rows before those fetched (i.e.
 320          *     if a "previous" link would make sense)
 321          * @param int $limit Exact query limit
 322          * @param IResultWrapper $res
 323          */
 324         function extractResultInfo( $isFirst, $limit, IResultWrapper $res ) {
 325                 $numRows = $res->numRows();
 326                 if ( $numRows ) {
 327                         # Remove any table prefix from index field
 328                         $parts = explode( '.', $this->mIndexField );
 329                         $indexColumn = end( $parts );
 330
 331                         $row = $res->fetchRow();
 332                         $firstIndex = $row[$indexColumn];
 333
 334                         # Discard the extra result row if there is one
 335                         if ( $numRows > $this->mLimit && $numRows > 1 ) {
 336                                 $res->seek( $numRows - 1 );
 337                                 $this->mPastTheEndRow = $res->fetchObject();
 338                                 $this->mPastTheEndIndex = $this->mPastTheEndRow->$indexColumn;
 339                                 $res->seek( $numRows - 2 );
 340                                 $row = $res->fetchRow();
 341                                 $lastIndex = $row[$indexColumn];
 342                         } else {
 343                                 $this->mPastTheEndRow = null;
 344                                 # Setting indexes to an empty string means that they will be
 345                                 # omitted if they would otherwise appear in URLs. It just so
 346                                 # happens that this  is the right thing to do in the standard
 347                                 # UI, in all the relevant cases.
 348                                 $this->mPastTheEndIndex = '';
 349                                 $res->seek( $numRows - 1 );
 350                                 $row = $res->fetchRow();
 351                                 $lastIndex = $row[$indexColumn];
 352                         }
 353                 } else {
 354                         $firstIndex = '';
 355                         $lastIndex = '';
 356                         $this->mPastTheEndRow = null;
 357                         $this->mPastTheEndIndex = '';
 358                 }
 359
 360                 if ( $this->mIsBackwards ) {
 361                         $this->mIsFirst = ( $numRows < $limit );
 362                         $this->mIsLast = $isFirst;
 363                         $this->mLastShown = $firstIndex;
 364                         $this->mFirstShown = $lastIndex;
 365                 } else {
 366                         $this->mIsFirst = $isFirst;
 367                         $this->mIsLast = ( $numRows < $limit );
 368                         $this->mLastShown = $lastIndex;
 369                         $this->mFirstShown = $firstIndex;
 370                 }
 371         }
 372
 373         /**
 374          * Get some text to go in brackets in the "function name" part of the SQL comment
 375          *
 376          * @return string
 377          */
 378         function getSqlComment() {
 379                 return static::class;
 380         }
 381
 382         /**
 383          * Do a query with specified parameters, rather than using the object
 384          * context
 385          *
 386          * @param string $offset Index offset, inclusive
 387          * @param int $limit Exact query limit
 388          * @param bool $descending Query direction, false for ascending, true for descending
 389          * @return IResultWrapper
 390          */
 391         public function reallyDoQuery( $offset, $limit, $descending ) {
 392                 list( $tables, $fields, $conds, $fname, $options, $join_conds ) =
 393                         $this->buildQueryInfo( $offset, $limit, $descending );
 394
 395                 return $this->mDb->select( $tables, $fields, $conds, $fname, $options, $join_conds );
 396         }
 397
 398         /**
 399          * Build variables to use by the database wrapper.
 400          *
 401          * @param string $offset Index offset, inclusive
 402          * @param int $limit Exact query limit
 403          * @param bool $descending Query direction, false for ascending, true for descending
 404          * @return array
 405          */
 406         protected function buildQueryInfo( $offset, $limit, $descending ) {
 407                 $fname = __METHOD__ . ' (' . $this->getSqlComment() . ')';
 408                 $info = $this->getQueryInfo();
 409                 $tables = $info['tables'];
 410                 $fields = $info['fields'];
 411                 $conds = $info['conds'] ?? [];
 412                 $options = $info['options'] ?? [];
 413                 $join_conds = $info['join_conds'] ?? [];
 414                 $sortColumns = array_merge( [ $this->mIndexField ], $this->mExtraSortFields );
 415                 if ( $descending ) {
 416                         $options['ORDER BY'] = $sortColumns;
 417                         $operator = $this->mIncludeOffset ? '>=' : '>';
 418                 } else {
 419                         $orderBy = [];
 420                         foreach ( $sortColumns as $col ) {
 421                                 $orderBy[] = $col . ' DESC';
 422                         }
 423                         $options['ORDER BY'] = $orderBy;
 424                         $operator = $this->mIncludeOffset ? '<=' : '<';
 425                 }
 426                 if ( $offset != '' ) {
 427                         $conds[] = $this->mIndexField . $operator . $this->mDb->addQuotes( $offset );
 428                 }
 429                 $options['LIMIT'] = intval( $limit );
 430                 return [ $tables, $fields, $conds, $fname, $options, $join_conds ];
 431         }
 432
 433         /**
 434          * Pre-process results; useful for performing batch existence checks, etc.
 435          *
 436          * @param IResultWrapper $result
 437          */
 438         protected function preprocessResults( $result ) {
 439         }
 440
 441         /**
 442          * Get the formatted result list. Calls getStartBody(), formatRow() and
 443          * getEndBody(), concatenates the results and returns them.
 444          *
 445          * @return string
 446          */
 447         public function getBody() {
 448                 if ( !$this->mQueryDone ) {
 449                         $this->doQuery();
 450                 }
 451
 452                 if ( $this->mResult->numRows() ) {
 453                         # Do any special query batches before display
 454                         $this->doBatchLookups();
 455                 }
 456
 457                 # Don't use any extra rows returned by the query
 458                 $numRows = min( $this->mResult->numRows(), $this->mLimit );
 459
 460                 $s = $this->getStartBody();
 461                 if ( $numRows ) {
 462                         if ( $this->mIsBackwards ) {
 463                                 for ( $i = $numRows - 1; $i >= 0; $i-- ) {
 464                                         $this->mResult->seek( $i );
 465                                         $row = $this->mResult->fetchObject();
 466                                         $s .= $this->formatRow( $row );
 467                                 }
 468                         } else {
 469                                 $this->mResult->seek( 0 );
 470                                 for ( $i = 0; $i < $numRows; $i++ ) {
 471                                         $row = $this->mResult->fetchObject();
 472                                         $s .= $this->formatRow( $row );
 473                                 }
 474                         }
 475                 } else {
 476                         $s .= $this->getEmptyBody();
 477                 }
 478                 $s .= $this->getEndBody();
 479                 return $s;
 480         }
 481
 482         /**
 483          * Make a self-link
 484          *
 485          * @param string $text Text displayed on the link
 486          * @param array|null $query Associative array of parameter to be in the query string
 487          * @param string|null $type Link type used to create additional attributes, like "rel", "class" or
 488          *  "title". Valid values (non-exhaustive list): 'first', 'last', 'prev', 'next', 'asc', 'desc'.
 489          * @return string HTML fragment
 490          */
 491         function makeLink( $text, array $query = null, $type = null ) {
 492                 if ( $query === null ) {
 493                         return $text;
 494                 }
 495
 496                 $attrs = [];
 497                 if ( in_array( $type, [ 'prev', 'next' ] ) ) {
 498                         $attrs['rel'] = $type;
 499                 }
 500
 501                 if ( in_array( $type, [ 'asc', 'desc' ] ) ) {
 502                         $attrs['title'] = $this->msg( $type == 'asc' ? 'sort-ascending' : 'sort-descending' )->text();
 503                 }
 504
 505                 if ( $type ) {
 506                         $attrs['class'] = "mw-{$type}link";
 507                 }
 508
 509                 return Linker::linkKnown(
 510                         $this->getTitle(),
 511                         $text,
 512                         $attrs,
 513                         $query + $this->getDefaultQuery()
 514                 );
 515         }
 516
 517         /**
 518          * Called from getBody(), before getStartBody() is called and
 519          * after doQuery() was called. This will be called only if there
 520          * are rows in the result set.
 521          *
 522          * @return void
 523          */
 524         protected function doBatchLookups() {
 525         }
 526
 527         /**
 528          * Hook into getBody(), allows text to be inserted at the start. This
 529          * will be called even if there are no rows in the result set.
 530          *
 531          * @return string
 532          */
 533         protected function getStartBody() {
 534                 return '';
 535         }
 536
 537         /**
 538          * Hook into getBody() for the end of the list
 539          *
 540          * @return string
 541          */
 542         protected function getEndBody() {
 543                 return '';
 544         }
 545
 546         /**
 547          * Hook into getBody(), for the bit between the start and the
 548          * end when there are no rows
 549          *
 550          * @return string
 551          */
 552         protected function getEmptyBody() {
 553                 return '';
 554         }
 555
 556         /**
 557          * Get an array of query parameters that should be put into self-links.
 558          * By default, all parameters passed in the URL are used, except for a
 559          * short blacklist.
 560          *
 561          * @return array Associative array
 562          */
 563         function getDefaultQuery() {
 564                 if ( !isset( $this->mDefaultQuery ) ) {
 565                         $this->mDefaultQuery = $this->getRequest()->getQueryValues();
 566                         unset( $this->mDefaultQuery['title'] );
 567                         unset( $this->mDefaultQuery['dir'] );
 568                         unset( $this->mDefaultQuery['offset'] );
 569                         unset( $this->mDefaultQuery['limit'] );
 570                         unset( $this->mDefaultQuery['order'] );
 571                         unset( $this->mDefaultQuery['month'] );
 572                         unset( $this->mDefaultQuery['year'] );
 573                 }
 574                 return $this->mDefaultQuery;
 575         }
 576
 577         /**
 578          * Get the number of rows in the result set
 579          *
 580          * @return int
 581          */
 582         function getNumRows() {
 583                 if ( !$this->mQueryDone ) {
 584                         $this->doQuery();
 585                 }
 586                 return $this->mResult->numRows();
 587         }
 588
 589         /**
 590          * Get a URL query array for the prev, next, first and last links.
 591          *
 592          * @return array
 593          */
 594         function getPagingQueries() {
 595                 if ( !$this->mQueryDone ) {
 596                         $this->doQuery();
 597                 }
 598
 599                 # Don't announce the limit everywhere if it's the default
 600                 $urlLimit = $this->mLimit == $this->mDefaultLimit ? null : $this->mLimit;
 601
 602                 if ( $this->mIsFirst ) {
 603                         $prev = false;
 604                         $first = false;
 605                 } else {
 606                         $prev = [
 607                                 'dir' => 'prev',
 608                                 'offset' => $this->mFirstShown,
 609                                 'limit' => $urlLimit
 610                         ];
 611                         $first = [ 'limit' => $urlLimit ];
 612                 }
 613                 if ( $this->mIsLast ) {
 614                         $next = false;
 615                         $last = false;
 616                 } else {
 617                         $next = [ 'offset' => $this->mLastShown, 'limit' => $urlLimit ];
 618                         $last = [ 'dir' => 'prev', 'limit' => $urlLimit ];
 619                 }
 620                 return [
 621                         'prev' => $prev,
 622                         'next' => $next,
 623                         'first' => $first,
 624                         'last' => $last
 625                 ];
 626         }
 627
 628         /**
 629          * Returns whether to show the "navigation bar"
 630          *
 631          * @return bool
 632          */
 633         function isNavigationBarShown() {
 634                 if ( !$this->mQueryDone ) {
 635                         $this->doQuery();
 636                 }
 637                 // Hide navigation by default if there is nothing to page
 638                 return !( $this->mIsFirst && $this->mIsLast );
 639         }
 640
 641         /**
 642          * Get paging links. If a link is disabled, the item from $disabledTexts
 643          * will be used. If there is no such item, the unlinked text from
 644          * $linkTexts will be used. Both $linkTexts and $disabledTexts are arrays
 645          * of HTML.
 646          *
 647          * @param array $linkTexts
 648          * @param array $disabledTexts
 649          * @return array
 650          */
 651         function getPagingLinks( $linkTexts, $disabledTexts = [] ) {
 652                 $queries = $this->getPagingQueries();
 653                 $links = [];
 654
 655                 foreach ( $queries as $type => $query ) {
 656                         if ( $query !== false ) {
 657                                 $links[$type] = $this->makeLink(
 658                                         $linkTexts[$type],
 659                                         $queries[$type],
 660                                         $type
 661                                 );
 662                         } elseif ( isset( $disabledTexts[$type] ) ) {
 663                                 $links[$type] = $disabledTexts[$type];
 664                         } else {
 665                                 $links[$type] = $linkTexts[$type];
 666                         }
 667                 }
 668
 669                 return $links;
 670         }
 671
 672         function getLimitLinks() {
 673                 $links = [];
 674                 if ( $this->mIsBackwards ) {
 675                         $offset = $this->mPastTheEndIndex;
 676                 } else {
 677                         $offset = $this->mOffset;
 678                 }
 679                 foreach ( $this->mLimitsShown as $limit ) {
 680                         $links[] = $this->makeLink(
 681                                 $this->getLanguage()->formatNum( $limit ),
 682                                 [ 'offset' => $offset, 'limit' => $limit ],
 683                                 'num'
 684                         );
 685                 }
 686                 return $links;
 687         }
 688
 689         /**
 690          * Abstract formatting function. This should return an HTML string
 691          * representing the result row $row. Rows will be concatenated and
 692          * returned by getBody()
 693          *
 694          * @param array|stdClass $row Database row
 695          * @return string
 696          */
 697         abstract function formatRow( $row );
 698
 699         /**
 700          * This function should be overridden to provide all parameters
 701          * needed for the main paged query. It returns an associative
 702          * array with the following elements:
 703          *    tables => Table(s) for passing to Database::select()
 704          *    fields => Field(s) for passing to Database::select(), may be *
 705          *    conds => WHERE conditions
 706          *    options => option array
 707          *    join_conds => JOIN conditions
 708          *
 709          * @return array
 710          */
 711         abstract function getQueryInfo();
 712
 713         /**
 714          * This function should be overridden to return the name of the index fi-
 715          * eld.  If the pager supports multiple orders, it may return an array of
 716          * 'querykey' => 'indexfield' pairs, so that a request with &count=querykey
 717          * will use indexfield to sort.  In this case, the first returned key is
 718          * the default.
 719          *
 720          * Needless to say, it's really not a good idea to use a non-unique index
 721          * for this!  That won't page right.
 722          *
 723          * @return string|string[]
 724          */
 725         abstract function getIndexField();
 726
 727         /**
 728          * This function should be overridden to return the names of secondary columns
 729          * to order by in addition to the column in getIndexField(). These fields will
 730          * not be used in the pager offset or in any links for users.
 731          *
 732          * If getIndexField() returns an array of 'querykey' => 'indexfield' pairs then
 733          * this must return a corresponding array of 'querykey' => [ fields... ] pairs
 734          * in order for a request with &count=querykey to use [ fields... ] to sort.
 735          *
 736          * This is useful for pagers that GROUP BY a unique column (say page_id)
 737          * and ORDER BY another (say page_len). Using GROUP BY and ORDER BY both on
 738          * page_len,page_id avoids temp tables (given a page_len index). This would
 739          * also work if page_id was non-unique but we had a page_len,page_id index.
 740          *
 741          * @return string[]|array[]
 742          */
 743         protected function getExtraSortFields() {
 744                 return [];
 745         }
 746
 747         /**
 748          * Return the default sorting direction: DIR_ASCENDING or DIR_DESCENDING.
 749          * You can also have an associative array of ordertype => dir,
 750          * if multiple order types are supported.  In this case getIndexField()
 751          * must return an array, and the keys of that must exactly match the keys
 752          * of this.
 753          *
 754          * For backward compatibility, this method's return value will be ignored
 755          * if $this->mDefaultDirection is already set when the constructor is
 756          * called, for instance if it's statically initialized.  In that case the
 757          * value of that variable (which must be a boolean) will be used.
 758          *
 759          * Note that despite its name, this does not return the value of the
 760          * $this->mDefaultDirection member variable.  That's the default for this
 761          * particular instantiation, which is a single value.  This is the set of
 762          * all defaults for the class.
 763          *
 764          * @return bool
 765          */
 766         protected function getDefaultDirections() {
 767                 return self::DIR_ASCENDING;
 768         }
 769 }