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 use MediaWiki\Linker\LinkTarget;
  27 use MediaWiki\Navigation\PrevNextNavigationRenderer;
  28
  29 /**
  30  * IndexPager is an efficient pager which uses a (roughly unique) index in the
  31  * data set to implement paging, rather than a "LIMIT offset,limit" clause.
  32  * In MySQL, such a limit/offset clause requires counting through the
  33  * specified number of offset rows to find the desired data, which can be
  34  * expensive for large offsets.
  35  *
  36  * ReverseChronologicalPager is a child class of the abstract IndexPager, and
  37  * contains  some formatting and display code which is specific to the use of
  38  * timestamps as  indexes. Here is a synopsis of its operation:
  39  *
  40  *    * The query is specified by the offset, limit and direction (dir)
  41  *      parameters, in addition to any subclass-specific parameters.
  42  *    * The offset is the non-inclusive start of the DB query. A row with an
  43  *      index value equal to the offset will never be shown.
  44  *    * The query may either be done backwards, where the rows are returned by
  45  *      the database in the opposite order to which they are displayed to the
  46  *      user, or forwards. This is specified by the "dir" parameter, dir=prev
  47  *      means backwards, anything else means forwards. The offset value
  48  *      specifies the start of the database result set, which may be either
  49  *      the start or end of the displayed data set. This allows "previous"
  50  *      links to be implemented without knowledge of the index value at the
  51  *      start of the previous page.
  52  *    * An additional row beyond the user-specified limit is always requested.
  53  *      This allows us to tell whether we should display a "next" link in the
  54  *      case of forwards mode, or a "previous" link in the case of backwards
  55  *      mode. Determining whether to display the other link (the one for the
  56  *      page before the start of the database result set) can be done
  57  *      heuristically by examining the offset.
  58  *
  59  *    * An empty offset indicates that the offset condition should be omitted
  60  *      from the query. This naturally produces either the first page or the
  61  *      last page depending on the dir parameter.
  62  *
  63  *  Subclassing the pager to implement concrete functionality should be fairly
  64  *  simple, please see the examples in HistoryAction.php and
  65  *  SpecialBlockList.php. You just need to override formatRow(),
  66  *  getQueryInfo() and getIndexField(). Don't forget to call the parent
  67  *  constructor if you override it.
  68  *
  69  * @ingroup Pager
  70  */
  71 abstract class IndexPager extends ContextSource implements Pager {
  72         /** Backwards-compatible constant for $mDefaultDirection field (do not change) */
  73         const DIR_ASCENDING = false;
  74         /** Backwards-compatible constant for $mDefaultDirection field (do not change) */
  75         const DIR_DESCENDING = true;
  76
  77         /** Backwards-compatible constant for reallyDoQuery() (do not change) */
  78         const QUERY_ASCENDING = true;
  79         /** Backwards-compatible constant for reallyDoQuery() (do not change) */
  80         const QUERY_DESCENDING = false;
  81
  82         /** @var WebRequest */
  83         public $mRequest;
  84         /** @var int[] List of default entry limit options to be presented to clients */
  85         public $mLimitsShown = [ 20, 50, 100, 250, 500 ];
  86         /** @var int The default entry limit choosen for clients */
  87         public $mDefaultLimit = 50;
  88         /** @var mixed The starting point to enumerate entries */
  89         public $mOffset;
  90         /** @var int The maximum number of entries to show */
  91         public $mLimit;
  92         /** @var bool Whether the listing query completed */
  93         public $mQueryDone = false;
  94         /** @var IDatabase */
  95         public $mDb;
  96         /** @var stdClass|bool|null Extra row fetched at the end to see if the end was reached */
  97         public $mPastTheEndRow;
  98
  99         /**
 100          * The index to actually be used for ordering. This is a single column,
 101          * for one ordering, even if multiple orderings are supported.
 102          * @var string
 103          */
 104         protected $mIndexField;
 105         /**
 106          * An array of secondary columns to order by. These fields are not part of the offset.
 107          * This is a column list for one ordering, even if multiple orderings are supported.
 108          * @var string[]
 109          */
 110         protected $mExtraSortFields;
 111         /** For pages that support multiple types of ordering, which one to use.
 112          * @var string|null
 113          */
 114         protected $mOrderType;
 115         /**
 116          * $mDefaultDirection gives the direction to use when sorting results:
 117          * DIR_ASCENDING or DIR_DESCENDING. If $mIsBackwards is set, we start from
 118          * the opposite end, but we still sort the page itself according to
 119          * $mDefaultDirection. For example, if $mDefaultDirection is DIR_ASCENDING
 120          * but we're going backwards, we'll display the last page of results, but
 121          * the last result will be at the bottom, not the top.
 122          *
 123          * Like $mIndexField, $mDefaultDirection will be a single value even if the
 124          * class supports multiple default directions for different order types.
 125          * @var bool
 126          */
 127         public $mDefaultDirection;
 128         /** @var bool */
 129         public $mIsBackwards;
 130
 131         /** @var bool True if the current result set is the first one */
 132         public $mIsFirst;
 133         /** @var bool */
 134         public $mIsLast;
 135
 136         /** @var mixed */
 137         protected $mLastShown;
 138         /** @var mixed */
 139         protected $mFirstShown;
 140         /** @var mixed */
 141         protected $mPastTheEndIndex;
 142         /** @var array */
 143         protected $mDefaultQuery;
 144         /** @var string */
 145         protected $mNavigationBar;
 146
 147         /**
 148          * Whether to include the offset in the query
 149          * @var bool
 150          */
 151         protected $mIncludeOffset = false;
 152
 153         /**
 154          * Result object for the query. Warning: seek before use.
 155          *
 156          * @var IResultWrapper
 157          */
 158         public $mResult;
 159
 160         public function __construct( IContextSource $context = null ) {
 161                 if ( $context ) {
 162                         $this->setContext( $context );
 163                 }
 164
 165                 $this->mRequest = $this->getRequest();
 166
 167                 # NB: the offset is quoted, not validated. It is treated as an
 168                 # arbitrary string to support the widest variety of index types. Be
 169                 # careful outputting it into HTML!
 170                 $this->mOffset = $this->mRequest->getText( 'offset' );
 171
 172                 # Use consistent behavior for the limit options
 173                 $this->mDefaultLimit = $this->getUser()->getIntOption( 'rclimit' );
 174                 if ( !$this->mLimit ) {
 175                         // Don't override if a subclass calls $this->setLimit() in its constructor.
 176                         list( $this->mLimit, /* $offset */ ) = $this->mRequest->getLimitOffset();
 177                 }
 178
 179                 $this->mIsBackwards = ( $this->mRequest->getVal( 'dir' ) == 'prev' );
 180                 # Let the subclass set the DB here; otherwise use a replica DB for the current wiki
 181                 $this->mDb = $this->mDb ?: wfGetDB( DB_REPLICA );
 182
 183                 $index = $this->getIndexField(); // column to sort on
 184                 $extraSort = $this->getExtraSortFields(); // extra columns to sort on for query planning
 185                 $order = $this->mRequest->getVal( 'order' );
 186                 if ( is_array( $index ) && isset( $index[$order] ) ) {
 187                         $this->mOrderType = $order;
 188                         $this->mIndexField = $index[$order];
 189                         $this->mExtraSortFields = isset( $extraSort[$order] )
 190                                 ? (array)$extraSort[$order]
 191                                 : [];
 192                 } elseif ( is_array( $index ) ) {
 193                         # First element is the default
 194                         $this->mIndexField = reset( $index );
 195                         $this->mOrderType = key( $index );
 196                         $this->mExtraSortFields = isset( $extraSort[$this->mOrderType] )
 197                                 ? (array)$extraSort[$this->mOrderType]
 198                                 : [];
 199                 } else {
 200                         # $index is not an array
 201                         $this->mOrderType = null;
 202                         $this->mIndexField = $index;
 203                         $this->mExtraSortFields = (array)$extraSort;
 204                 }
 205
 206                 if ( !isset( $this->mDefaultDirection ) ) {
 207                         $dir = $this->getDefaultDirections();
 208                         $this->mDefaultDirection = is_array( $dir )
 209                                 ? $dir[$this->mOrderType]
 210                                 : $dir;
 211                 }
 212         }
 213
 214         /**
 215          * Get the Database object in use
 216          *
 217          * @return IDatabase
 218          */
 219         public function getDatabase() {
 220                 return $this->mDb;
 221         }
 222
 223         /**
 224          * Do the query, using information from the object context. This function
 225          * has been kept minimal to make it overridable if necessary, to allow for
 226          * result sets formed from multiple DB queries.
 227          */
 228         public function doQuery() {
 229                 # Use the child class name for profiling
 230                 $fname = __METHOD__ . ' (' . static::class . ')';
 231                 /** @noinspection PhpUnusedLocalVariableInspection */
 232                 $section = Profiler::instance()->scopedProfileIn( $fname );
 233
 234                 $defaultOrder = ( $this->mDefaultDirection === self::DIR_ASCENDING )
 235                         ? self::QUERY_ASCENDING
 236                         : self::QUERY_DESCENDING;
 237                 $order = $this->mIsBackwards ? self::oppositeOrder( $defaultOrder ) : $defaultOrder;
 238
 239                 # Plus an extra row so that we can tell the "next" link should be shown
 240                 $queryLimit = $this->mLimit + 1;
 241
 242                 if ( $this->mOffset == '' ) {
 243                         $isFirst = true;
 244                 } else {
 245                         // If there's an offset, we may or may not be at the first entry.
 246                         // The only way to tell is to run the query in the opposite
 247                         // direction see if we get a row.
 248                         $oldIncludeOffset = $this->mIncludeOffset;
 249                         $this->mIncludeOffset = !$this->mIncludeOffset;
 250                         $oppositeOrder = self::oppositeOrder( $order );
 251                         $isFirst = !$this->reallyDoQuery( $this->mOffset, 1, $oppositeOrder )->numRows();
 252                         $this->mIncludeOffset = $oldIncludeOffset;
 253                 }
 254
 255                 $this->mResult = $this->reallyDoQuery(
 256                         $this->mOffset,
 257                         $queryLimit,
 258                         $order
 259                 );
 260
 261                 $this->extractResultInfo( $isFirst, $queryLimit, $this->mResult );
 262                 $this->mQueryDone = true;
 263
 264                 $this->preprocessResults( $this->mResult );
 265                 $this->mResult->rewind(); // Paranoia
 266         }
 267
 268         /**
 269          * @param bool $order One of the IndexPager::QUERY_* class constants
 270          * @return bool The opposite query order as an IndexPager::QUERY_ constant
 271          */
 272         final protected static function oppositeOrder( $order ) {
 273                 return ( $order === self::QUERY_ASCENDING )
 274                         ? self::QUERY_DESCENDING
 275                         : self::QUERY_ASCENDING;
 276         }
 277
 278         /**
 279          * @return IResultWrapper The result wrapper.
 280          */
 281         function getResult() {
 282                 return $this->mResult;
 283         }
 284
 285         /**
 286          * Set the offset from an other source than the request
 287          *
 288          * @param int|string $offset
 289          */
 290         function setOffset( $offset ) {
 291                 $this->mOffset = $offset;
 292         }
 293
 294         /**
 295          * Set the limit from an other source than the request
 296          *
 297          * Verifies limit is between 1 and 5000
 298          *
 299          * @param int|string $limit
 300          */
 301         function setLimit( $limit ) {
 302                 $limit = (int)$limit;
 303                 // WebRequest::getLimitOffset() puts a cap of 5000, so do same here.
 304                 if ( $limit > 5000 ) {
 305                         $limit = 5000;
 306                 }
 307                 if ( $limit > 0 ) {
 308                         $this->mLimit = $limit;
 309                 }
 310         }
 311
 312         /**
 313          * Get the current limit
 314          *
 315          * @return int
 316          */
 317         function getLimit() {
 318                 return $this->mLimit;
 319         }
 320
 321         /**
 322          * Set whether a row matching exactly the offset should be also included
 323          * in the result or not. By default this is not the case, but when the
 324          * offset is user-supplied this might be wanted.
 325          *
 326          * @param bool $include
 327          */
 328         public function setIncludeOffset( $include ) {
 329                 $this->mIncludeOffset = $include;
 330         }
 331
 332         /**
 333          * Extract some useful data from the result object for use by
 334          * the navigation bar, put it into $this
 335          *
 336          * @param bool $isFirst False if there are rows before those fetched (i.e.
 337          *     if a "previous" link would make sense)
 338          * @param int $limit Exact query limit
 339          * @param IResultWrapper $res
 340          */
 341         function extractResultInfo( $isFirst, $limit, IResultWrapper $res ) {
 342                 $numRows = $res->numRows();
 343                 if ( $numRows ) {
 344                         # Remove any table prefix from index field
 345                         $parts = explode( '.', $this->mIndexField );
 346                         $indexColumn = end( $parts );
 347
 348                         $row = $res->fetchRow();
 349                         $firstIndex = $row[$indexColumn];
 350
 351                         # Discard the extra result row if there is one
 352                         if ( $numRows > $this->mLimit && $numRows > 1 ) {
 353                                 $res->seek( $numRows - 1 );
 354                                 $this->mPastTheEndRow = $res->fetchObject();
 355                                 $this->mPastTheEndIndex = $this->mPastTheEndRow->$indexColumn;
 356                                 $res->seek( $numRows - 2 );
 357                                 $row = $res->fetchRow();
 358                                 $lastIndex = $row[$indexColumn];
 359                         } else {
 360                                 $this->mPastTheEndRow = null;
 361                                 # Setting indexes to an empty string means that they will be
 362                                 # omitted if they would otherwise appear in URLs. It just so
 363                                 # happens that this  is the right thing to do in the standard
 364                                 # UI, in all the relevant cases.
 365                                 $this->mPastTheEndIndex = '';
 366                                 $res->seek( $numRows - 1 );
 367                                 $row = $res->fetchRow();
 368                                 $lastIndex = $row[$indexColumn];
 369                         }
 370                 } else {
 371                         $firstIndex = '';
 372                         $lastIndex = '';
 373                         $this->mPastTheEndRow = null;
 374                         $this->mPastTheEndIndex = '';
 375                 }
 376
 377                 if ( $this->mIsBackwards ) {
 378                         $this->mIsFirst = ( $numRows < $limit );
 379                         $this->mIsLast = $isFirst;
 380                         $this->mLastShown = $firstIndex;
 381                         $this->mFirstShown = $lastIndex;
 382                 } else {
 383                         $this->mIsFirst = $isFirst;
 384                         $this->mIsLast = ( $numRows < $limit );
 385                         $this->mLastShown = $lastIndex;
 386                         $this->mFirstShown = $firstIndex;
 387                 }
 388         }
 389
 390         /**
 391          * Get some text to go in brackets in the "function name" part of the SQL comment
 392          *
 393          * @return string
 394          */
 395         function getSqlComment() {
 396                 return static::class;
 397         }
 398
 399         /**
 400          * Do a query with specified parameters, rather than using the object context
 401          *
 402          * @note For b/c, query direction is true for ascending and false for descending
 403          *
 404          * @param string $offset Index offset, inclusive
 405          * @param int $limit Exact query limit
 406          * @param bool $order IndexPager::QUERY_ASCENDING or IndexPager::QUERY_DESCENDING
 407          * @return IResultWrapper
 408          */
 409         public function reallyDoQuery( $offset, $limit, $order ) {
 410                 list( $tables, $fields, $conds, $fname, $options, $join_conds ) =
 411                         $this->buildQueryInfo( $offset, $limit, $order );
 412
 413                 return $this->mDb->select( $tables, $fields, $conds, $fname, $options, $join_conds );
 414         }
 415
 416         /**
 417          * Build variables to use by the database wrapper.
 418          *
 419          * @note For b/c, query direction is true for ascending and false for descending
 420          *
 421          * @param string $offset Index offset, inclusive
 422          * @param int $limit Exact query limit
 423          * @param bool $order IndexPager::QUERY_ASCENDING or IndexPager::QUERY_DESCENDING
 424          * @return array
 425          */
 426         protected function buildQueryInfo( $offset, $limit, $order ) {
 427                 $fname = __METHOD__ . ' (' . $this->getSqlComment() . ')';
 428                 $info = $this->getQueryInfo();
 429                 $tables = $info['tables'];
 430                 $fields = $info['fields'];
 431                 $conds = $info['conds'] ?? [];
 432                 $options = $info['options'] ?? [];
 433                 $join_conds = $info['join_conds'] ?? [];
 434                 $sortColumns = array_merge( [ $this->mIndexField ], $this->mExtraSortFields );
 435                 if ( $order === self::QUERY_ASCENDING ) {
 436                         $options['ORDER BY'] = $sortColumns;
 437                         $operator = $this->mIncludeOffset ? '>=' : '>';
 438                 } else {
 439                         $orderBy = [];
 440                         foreach ( $sortColumns as $col ) {
 441                                 $orderBy[] = $col . ' DESC';
 442                         }
 443                         $options['ORDER BY'] = $orderBy;
 444                         $operator = $this->mIncludeOffset ? '<=' : '<';
 445                 }
 446                 if ( $offset != '' ) {
 447                         $conds[] = $this->mIndexField . $operator . $this->mDb->addQuotes( $offset );
 448                 }
 449                 $options['LIMIT'] = intval( $limit );
 450                 return [ $tables, $fields, $conds, $fname, $options, $join_conds ];
 451         }
 452
 453         /**
 454          * Pre-process results; useful for performing batch existence checks, etc.
 455          *
 456          * @param IResultWrapper $result
 457          */
 458         protected function preprocessResults( $result ) {
 459         }
 460
 461         /**
 462          * Get the formatted result list. Calls getStartBody(), formatRow() and
 463          * getEndBody(), concatenates the results and returns them.
 464          *
 465          * @return string
 466          */
 467         public function getBody() {
 468                 if ( !$this->mQueryDone ) {
 469                         $this->doQuery();
 470                 }
 471
 472                 if ( $this->mResult->numRows() ) {
 473                         # Do any special query batches before display
 474                         $this->doBatchLookups();
 475                 }
 476
 477                 # Don't use any extra rows returned by the query
 478                 $numRows = min( $this->mResult->numRows(), $this->mLimit );
 479
 480                 $s = $this->getStartBody();
 481                 if ( $numRows ) {
 482                         if ( $this->mIsBackwards ) {
 483                                 for ( $i = $numRows - 1; $i >= 0; $i-- ) {
 484                                         $this->mResult->seek( $i );
 485                                         $row = $this->mResult->fetchObject();
 486                                         $s .= $this->formatRow( $row );
 487                                 }
 488                         } else {
 489                                 $this->mResult->seek( 0 );
 490                                 for ( $i = 0; $i < $numRows; $i++ ) {
 491                                         $row = $this->mResult->fetchObject();
 492                                         $s .= $this->formatRow( $row );
 493                                 }
 494                         }
 495                 } else {
 496                         $s .= $this->getEmptyBody();
 497                 }
 498                 $s .= $this->getEndBody();
 499                 return $s;
 500         }
 501
 502         /**
 503          * Make a self-link
 504          *
 505          * @param string $text Text displayed on the link
 506          * @param array|null $query Associative array of parameter to be in the query string
 507          * @param string|null $type Link type used to create additional attributes, like "rel", "class" or
 508          *  "title". Valid values (non-exhaustive list): 'first', 'last', 'prev', 'next', 'asc', 'desc'.
 509          * @return string HTML fragment
 510          */
 511         function makeLink( $text, array $query = null, $type = null ) {
 512                 if ( $query === null ) {
 513                         return $text;
 514                 }
 515
 516                 $attrs = [];
 517                 if ( in_array( $type, [ 'prev', 'next' ] ) ) {
 518                         $attrs['rel'] = $type;
 519                 }
 520
 521                 if ( in_array( $type, [ 'asc', 'desc' ] ) ) {
 522                         $attrs['title'] = $this->msg( $type == 'asc' ? 'sort-ascending' : 'sort-descending' )->text();
 523                 }
 524
 525                 if ( $type ) {
 526                         $attrs['class'] = "mw-{$type}link";
 527                 }
 528
 529                 return Linker::linkKnown(
 530                         $this->getTitle(),
 531                         $text,
 532                         $attrs,
 533                         $query + $this->getDefaultQuery()
 534                 );
 535         }
 536
 537         /**
 538          * Called from getBody(), before getStartBody() is called and
 539          * after doQuery() was called. This will be called only if there
 540          * are rows in the result set.
 541          *
 542          * @return void
 543          */
 544         protected function doBatchLookups() {
 545         }
 546
 547         /**
 548          * Hook into getBody(), allows text to be inserted at the start. This
 549          * will be called even if there are no rows in the result set.
 550          *
 551          * @return string
 552          */
 553         protected function getStartBody() {
 554                 return '';
 555         }
 556
 557         /**
 558          * Hook into getBody() for the end of the list
 559          *
 560          * @return string
 561          */
 562         protected function getEndBody() {
 563                 return '';
 564         }
 565
 566         /**
 567          * Hook into getBody(), for the bit between the start and the
 568          * end when there are no rows
 569          *
 570          * @return string
 571          */
 572         protected function getEmptyBody() {
 573                 return '';
 574         }
 575
 576         /**
 577          * Get an array of query parameters that should be put into self-links.
 578          * By default, all parameters passed in the URL are used, except for a
 579          * short blacklist.
 580          *
 581          * @return array Associative array
 582          */
 583         function getDefaultQuery() {
 584                 if ( !isset( $this->mDefaultQuery ) ) {
 585                         $this->mDefaultQuery = $this->getRequest()->getQueryValues();
 586                         unset( $this->mDefaultQuery['title'] );
 587                         unset( $this->mDefaultQuery['dir'] );
 588                         unset( $this->mDefaultQuery['offset'] );
 589                         unset( $this->mDefaultQuery['limit'] );
 590                         unset( $this->mDefaultQuery['order'] );
 591                         unset( $this->mDefaultQuery['month'] );
 592                         unset( $this->mDefaultQuery['year'] );
 593                 }
 594                 return $this->mDefaultQuery;
 595         }
 596
 597         /**
 598          * Get the number of rows in the result set
 599          *
 600          * @return int
 601          */
 602         function getNumRows() {
 603                 if ( !$this->mQueryDone ) {
 604                         $this->doQuery();
 605                 }
 606                 return $this->mResult->numRows();
 607         }
 608
 609         /**
 610          * Get a URL query array for the prev, next, first and last links.
 611          *
 612          * @return array
 613          */
 614         function getPagingQueries() {
 615                 if ( !$this->mQueryDone ) {
 616                         $this->doQuery();
 617                 }
 618
 619                 # Don't announce the limit everywhere if it's the default
 620                 $urlLimit = $this->mLimit == $this->mDefaultLimit ? null : $this->mLimit;
 621
 622                 if ( $this->mIsFirst ) {
 623                         $prev = false;
 624                         $first = false;
 625                 } else {
 626                         $prev = [
 627                                 'dir' => 'prev',
 628                                 'offset' => $this->mFirstShown,
 629                                 'limit' => $urlLimit
 630                         ];
 631                         $first = [ 'limit' => $urlLimit ];
 632                 }
 633                 if ( $this->mIsLast ) {
 634                         $next = false;
 635                         $last = false;
 636                 } else {
 637                         $next = [ 'offset' => $this->mLastShown, 'limit' => $urlLimit ];
 638                         $last = [ 'dir' => 'prev', 'limit' => $urlLimit ];
 639                 }
 640                 return [
 641                         'prev' => $prev,
 642                         'next' => $next,
 643                         'first' => $first,
 644                         'last' => $last
 645                 ];
 646         }
 647
 648         /**
 649          * Returns whether to show the "navigation bar"
 650          *
 651          * @return bool
 652          */
 653         function isNavigationBarShown() {
 654                 if ( !$this->mQueryDone ) {
 655                         $this->doQuery();
 656                 }
 657                 // Hide navigation by default if there is nothing to page
 658                 return !( $this->mIsFirst && $this->mIsLast );
 659         }
 660
 661         /**
 662          * Get paging links. If a link is disabled, the item from $disabledTexts
 663          * will be used. If there is no such item, the unlinked text from
 664          * $linkTexts will be used. Both $linkTexts and $disabledTexts are arrays
 665          * of HTML.
 666          *
 667          * @param array $linkTexts
 668          * @param array $disabledTexts
 669          * @return array
 670          */
 671         function getPagingLinks( $linkTexts, $disabledTexts = [] ) {
 672                 $queries = $this->getPagingQueries();
 673                 $links = [];
 674
 675                 foreach ( $queries as $type => $query ) {
 676                         if ( $query !== false ) {
 677                                 $links[$type] = $this->makeLink(
 678                                         $linkTexts[$type],
 679                                         $queries[$type],
 680                                         $type
 681                                 );
 682                         } elseif ( isset( $disabledTexts[$type] ) ) {
 683                                 $links[$type] = $disabledTexts[$type];
 684                         } else {
 685                                 $links[$type] = $linkTexts[$type];
 686                         }
 687                 }
 688
 689                 return $links;
 690         }
 691
 692         function getLimitLinks() {
 693                 $links = [];
 694                 if ( $this->mIsBackwards ) {
 695                         $offset = $this->mPastTheEndIndex;
 696                 } else {
 697                         $offset = $this->mOffset;
 698                 }
 699                 foreach ( $this->mLimitsShown as $limit ) {
 700                         $links[] = $this->makeLink(
 701                                 $this->getLanguage()->formatNum( $limit ),
 702                                 [ 'offset' => $offset, 'limit' => $limit ],
 703                                 'num'
 704                         );
 705                 }
 706                 return $links;
 707         }
 708
 709         /**
 710          * Abstract formatting function. This should return an HTML string
 711          * representing the result row $row. Rows will be concatenated and
 712          * returned by getBody()
 713          *
 714          * @param array|stdClass $row Database row
 715          * @return string
 716          */
 717         abstract function formatRow( $row );
 718
 719         /**
 720          * This function should be overridden to provide all parameters
 721          * needed for the main paged query. It returns an associative
 722          * array with the following elements:
 723          *    tables => Table(s) for passing to Database::select()
 724          *    fields => Field(s) for passing to Database::select(), may be *
 725          *    conds => WHERE conditions
 726          *    options => option array
 727          *    join_conds => JOIN conditions
 728          *
 729          * @return array
 730          */
 731         abstract function getQueryInfo();
 732
 733         /**
 734          * This function should be overridden to return the name of the index fi-
 735          * eld.  If the pager supports multiple orders, it may return an array of
 736          * 'querykey' => 'indexfield' pairs, so that a request with &count=querykey
 737          * will use indexfield to sort.  In this case, the first returned key is
 738          * the default.
 739          *
 740          * Needless to say, it's really not a good idea to use a non-unique index
 741          * for this!  That won't page right.
 742          *
 743          * @return string|string[]
 744          */
 745         abstract function getIndexField();
 746
 747         /**
 748          * This function should be overridden to return the names of secondary columns
 749          * to order by in addition to the column in getIndexField(). These fields will
 750          * not be used in the pager offset or in any links for users.
 751          *
 752          * If getIndexField() returns an array of 'querykey' => 'indexfield' pairs then
 753          * this must return a corresponding array of 'querykey' => [ fields... ] pairs
 754          * in order for a request with &count=querykey to use [ fields... ] to sort.
 755          *
 756          * This is useful for pagers that GROUP BY a unique column (say page_id)
 757          * and ORDER BY another (say page_len). Using GROUP BY and ORDER BY both on
 758          * page_len,page_id avoids temp tables (given a page_len index). This would
 759          * also work if page_id was non-unique but we had a page_len,page_id index.
 760          *
 761          * @return string[]|array[]
 762          */
 763         protected function getExtraSortFields() {
 764                 return [];
 765         }
 766
 767         /**
 768          * Return the default sorting direction: DIR_ASCENDING or DIR_DESCENDING.
 769          * You can also have an associative array of ordertype => dir,
 770          * if multiple order types are supported.  In this case getIndexField()
 771          * must return an array, and the keys of that must exactly match the keys
 772          * of this.
 773          *
 774          * For backward compatibility, this method's return value will be ignored
 775          * if $this->mDefaultDirection is already set when the constructor is
 776          * called, for instance if it's statically initialized.  In that case the
 777          * value of that variable (which must be a boolean) will be used.
 778          *
 779          * Note that despite its name, this does not return the value of the
 780          * $this->mDefaultDirection member variable.  That's the default for this
 781          * particular instantiation, which is a single value.  This is the set of
 782          * all defaults for the class.
 783          *
 784          * @return bool
 785          */
 786         protected function getDefaultDirections() {
 787                 return self::DIR_ASCENDING;
 788         }
 789
 790         /**
 791          * Generate (prev x| next x) (20|50|100...) type links for paging
 792          *
 793          * @param LinkTarget $title
 794          * @param int $offset
 795          * @param int $limit
 796          * @param array $query Optional URL query parameter string
 797          * @param bool $atend Optional param for specified if this is the last page
 798          * @return string
 799          */
 800         protected function buildPrevNextNavigation( LinkTarget $title, $offset, $limit,
 801                                                                                                 array $query = [], $atend = false
 802         ) {
 803                 $prevNext = new PrevNextNavigationRenderer( $this );
 804
 805                 return $prevNext->buildPrevNextNavigation( $title, $offset, $limit, $query,  $atend );
 806         }
 807 }