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