includes/Pager.php

   1 <?php
   2
   3 /**
   4  * Basic pager interface.
   5  */
   6 interface Pager {
   7         function getNavigationBar();
   8         function getBody();
   9 }
  10
  11 /**
  12  * IndexPager is an efficient pager which uses a (roughly unique) index in the
  13  * data set to implement paging, rather than a "LIMIT offset,limit" clause.
  14  * In MySQL, such a limit/offset clause requires counting through the specified number
  15  * of offset rows to find the desired data, which can be expensive for large offsets.
  16  *
  17  * ReverseChronologicalPager is a child class of the abstract IndexPager, and contains
  18  * some formatting and display code which is specific to the use of timestamps as
  19  * indexes. It is currently the only such child class. Here is a synopsis of the operation
  20  * of IndexPager and its primary subclass:
  21  *
  22  *    * The query is specified by the offset, limit and direction (dir) parameters, in
  23  *      addition to any subclass-specific parameters.
  24  *
  25  *    * The offset is the non-inclusive start of the DB query. A row with an index value
  26  *      equal to the offset will never be shown.
  27  *
  28  *    * The query may either be done backwards, where the rows are returned by the database
  29  *      in the opposite order to which they are displayed to the user, or forwards. This is
  30  *      specified by the "dir" parameter, dir=prev means backwards, anything else means
  31  *      forwards. The offset value specifies the start of the database result set, which
  32  *      may be either the start or end of the displayed data set. This allows "previous"
  33  *      links to be implemented without knowledge of the index value at the start of the
  34  *      previous page.
  35  *
  36  *    * An additional row beyond the user-specified limit is always requested. This allows
  37  *      us to tell whether we should display a "next" link in the case of forwards mode,
  38  *      or a "previous" link in the case of backwards mode. Determining whether to
  39  *      display the other link (the one for the page before the start of the database
  40  *      result set) can be done heuristically by examining the offset.
  41  *
  42  *    * An empty offset indicates that the offset condition should be omitted from the query.
  43  *      This naturally produces either the first page or the last page depending on the
  44  *      dir parameter.
  45  *
  46  *  Subclassing the pager to implement concrete functionality should be fairly simple,
  47  *  please see the examples in PageHistory.php and SpecialIpblocklist.php. You just need
  48  *  to override formatRow(), getQueryInfo() and getIndexField(). Don't forget to call the
  49  *  parent constructor if you override it.
  50  */
  51 abstract class IndexPager implements Pager {
  52         public $mRequest;
  53         public $mLimitsShown = array( 20, 50, 100, 250, 500 );
  54         public $mDefaultLimit = 50;
  55         public $mOffset, $mLimit;
  56         public $mQueryDone = false;
  57         public $mDb;
  58         public $mPastTheEndRow;
  59
  60         protected $mIndexField;
  61
  62         /**
  63          * Default query direction. false for ascending, true for descending
  64          */
  65         public $mDefaultDirection = false;
  66
  67         /**
  68          * Result object for the query. Warning: seek before use.
  69          */
  70         public $mResult;
  71
  72         function __construct() {
  73                 global $wgRequest;
  74                 $this->mRequest = $wgRequest;
  75
  76                 # NB: the offset is quoted, not validated. It is treated as an arbitrary string
  77                 # to support the widest variety of index types. Be careful outputting it into
  78                 # HTML!
  79                 $this->mOffset = $this->mRequest->getText( 'offset' );
  80                 $this->mLimit = $this->mRequest->getInt( 'limit', $this->mDefaultLimit );
  81                 if ( $this->mLimit <= 0 ) {
  82                         $this->mLimit = $this->mDefaultLimit;
  83                 }
  84                 $this->mIsBackwards = ( $this->mRequest->getVal( 'dir' ) == 'prev' );
  85                 $this->mIndexField = $this->getIndexField();
  86                 $this->mDb = wfGetDB( DB_SLAVE );
  87         }
  88
  89         /**
  90          * Do the query, using information from the object context. This function
  91          * has been kept minimal to make it overridable if necessary, to allow for
  92          * result sets formed from multiple DB queries.
  93          */
  94         function doQuery() {
  95                 # Use the child class name for profiling
  96                 $fname = __METHOD__ . ' (' . get_class( $this ) . ')';
  97                 wfProfileIn( $fname );
  98
  99                 $descending = ( $this->mIsBackwards == $this->mDefaultDirection );
 100                 # Plus an extra row so that we can tell the "next" link should be shown
 101                 $queryLimit = $this->mLimit + 1;
 102
 103                 $this->mResult = $this->reallyDoQuery( $this->mOffset, $queryLimit, $descending );
 104                 $this->extractResultInfo( $this->mOffset, $queryLimit, $this->mResult );
 105                 $this->mQueryDone = true;
 106
 107                 wfProfileOut( $fname );
 108         }
 109
 110         /**
 111          * Extract some useful data from the result object for use by
 112          * the navigation bar, put it into $this
 113          */
 114         function extractResultInfo( $offset, $limit, ResultWrapper $res ) {
 115                 $numRows = $res->numRows();
 116                 if ( $numRows ) {
 117                         $row = $res->fetchRow();
 118                         $firstIndex = $row[$this->mIndexField];
 119
 120                         # Discard the extra result row if there is one
 121                         if ( $numRows > $this->mLimit && $numRows > 1 ) {
 122                                 $res->seek( $numRows - 1 );
 123                                 $this->mPastTheEndRow = $res->fetchObject();
 124                                 $indexField = $this->mIndexField;
 125                                 $this->mPastTheEndIndex = $this->mPastTheEndRow->$indexField;
 126                                 $res->seek( $numRows - 2 );
 127                                 $row = $res->fetchRow();
 128                                 $lastIndex = $row[$this->mIndexField];
 129                         } else {
 130                                 $this->mPastTheEndRow = null;
 131                                 # Setting indexes to an empty string means that they will be omitted
 132                                 # if they would otherwise appear in URLs. It just so happens that this
 133                                 # is the right thing to do in the standard UI, in all the relevant cases.
 134                                 $this->mPastTheEndIndex = '';
 135                                 $res->seek( $numRows - 1 );
 136                                 $row = $res->fetchRow();
 137                                 $lastIndex = $row[$this->mIndexField];
 138                         }
 139                 } else {
 140                         $firstIndex = '';
 141                         $lastIndex = '';
 142                         $this->mPastTheEndRow = null;
 143                         $this->mPastTheEndIndex = '';
 144                 }
 145
 146                 if ( $this->mIsBackwards ) {
 147                         $this->mIsFirst = ( $numRows < $limit );
 148                         $this->mIsLast = ( $offset == '' );
 149                         $this->mLastShown = $firstIndex;
 150                         $this->mFirstShown = $lastIndex;
 151                 } else {
 152                         $this->mIsFirst = ( $offset == '' );
 153                         $this->mIsLast = ( $numRows < $limit );
 154                         $this->mLastShown = $lastIndex;
 155                         $this->mFirstShown = $firstIndex;
 156                 }
 157         }
 158
 159         /**
 160          * Do a query with specified parameters, rather than using the object context
 161          *
 162          * @param string $offset Index offset, inclusive
 163          * @param integer $limit Exact query limit
 164          * @param boolean $descending Query direction, false for ascending, true for descending
 165          * @return ResultWrapper
 166          */
 167         function reallyDoQuery( $offset, $limit, $ascending ) {
 168                 $fname = __METHOD__ . ' (' . get_class( $this ) . ')';
 169                 $info = $this->getQueryInfo();
 170                 $tables = $info['tables'];
 171                 $fields = $info['fields'];
 172                 $conds = isset( $info['conds'] ) ? $info['conds'] : array();
 173                 $options = isset( $info['options'] ) ? $info['options'] : array();
 174                 if ( $ascending ) {
 175                         $options['ORDER BY'] = $this->mIndexField;
 176                         $operator = '>';
 177                 } else {
 178                         $options['ORDER BY'] = $this->mIndexField . ' DESC';
 179                         $operator = '<';
 180                 }
 181                 if ( $offset != '' ) {
 182                         $conds[] = $this->mIndexField . $operator . $this->mDb->addQuotes( $offset );
 183                 }
 184                 $options['LIMIT'] = intval( $limit );
 185                 $res = $this->mDb->select( $tables, $fields, $conds, $fname, $options );
 186                 return new ResultWrapper( $this->mDb, $res );
 187         }
 188
 189         /**
 190          * Get the formatted result list. Calls getStartBody(), formatRow() and
 191          * getEndBody(), concatenates the results and returns them.
 192          */
 193         function getBody() {
 194                 if ( !$this->mQueryDone ) {
 195                         $this->doQuery();
 196                 }
 197                 # Don't use any extra rows returned by the query
 198                 $numRows = min( $this->mResult->numRows(), $this->mLimit );
 199
 200                 $s = $this->getStartBody();
 201                 if ( $numRows ) {
 202                         if ( $this->mIsBackwards ) {
 203                                 for ( $i = $numRows - 1; $i >= 0; $i-- ) {
 204                                         $this->mResult->seek( $i );
 205                                         $row = $this->mResult->fetchObject();
 206                                         $s .= $this->formatRow( $row );
 207                                 }
 208                         } else {
 209                                 $this->mResult->seek( 0 );
 210                                 for ( $i = 0; $i < $numRows; $i++ ) {
 211                                         $row = $this->mResult->fetchObject();
 212                                         $s .= $this->formatRow( $row );
 213                                 }
 214                         }
 215                 }
 216                 $s .= $this->getEndBody();
 217                 return $s;
 218         }
 219
 220         /**
 221          * Make a self-link
 222          */
 223         function makeLink($text, $query = NULL) {
 224                 if ( $query === null ) {
 225                         return $text;
 226                 } else {
 227                         return $this->getSkin()->makeKnownLinkObj( $this->getTitle(), $text,
 228                                 wfArrayToCGI( $query, $this->getDefaultQuery() ) );
 229                 }
 230         }
 231
 232         /**
 233          * Hook into getBody(), allows text to be inserted at the start. This
 234          * will be called even if there are no rows in the result set.
 235          */
 236         function getStartBody() {
 237                 return '';
 238         }
 239
 240         /**
 241          * Hook into getBody() for the end of the list
 242          */
 243         function getEndBody() {
 244                 return '';
 245         }
 246
 247         /**
 248          * Title used for self-links. Override this if you want to be able to
 249          * use a title other than $wgTitle
 250          */
 251         function getTitle() {
 252                 return $GLOBALS['wgTitle'];
 253         }
 254
 255         /**
 256          * Get the current skin. This can be overridden if necessary.
 257          */
 258         function getSkin() {
 259                 if ( !isset( $this->mSkin ) ) {
 260                         global $wgUser;
 261                         $this->mSkin = $wgUser->getSkin();
 262                 }
 263                 return $this->mSkin;
 264         }
 265
 266         /**
 267          * Get an array of query parameters that should be put into self-links.
 268          * By default, all parameters passed in the URL are used, except for a
 269          * short blacklist.
 270          */
 271         function getDefaultQuery() {
 272                 if ( !isset( $this->mDefaultQuery ) ) {
 273                         $this->mDefaultQuery = $_GET;
 274                         unset( $this->mDefaultQuery['title'] );
 275                         unset( $this->mDefaultQuery['dir'] );
 276                         unset( $this->mDefaultQuery['offset'] );
 277                         unset( $this->mDefaultQuery['limit'] );
 278                 }
 279                 return $this->mDefaultQuery;
 280         }
 281
 282         /**
 283          * Get the number of rows in the result set
 284          */
 285         function getNumRows() {
 286                 if ( !$this->mQueryDone ) {
 287                         $this->doQuery();
 288                 }
 289                 return $this->mResult->numRows();
 290         }
 291
 292         /**
 293          * Abstract formatting function. This should return an HTML string
 294          * representing the result row $row. Rows will be concatenated and
 295          * returned by getBody()
 296          */
 297         abstract function formatRow( $row );
 298
 299         /**
 300          * This function should be overridden to provide all parameters
 301          * needed for the main paged query. It returns an associative
 302          * array with the following elements:
 303          *    tables => Table(s) for passing to Database::select()
 304          *    fields => Field(s) for passing to Database::select(), may be *
 305          *    conds => WHERE conditions
 306          *    options => option array
 307          */
 308         abstract function getQueryInfo();
 309
 310         /**
 311          * This function should be overridden to return the name of the
 312          * index field.
 313          */
 314         abstract function getIndexField();
 315 }
 316
 317 /**
 318  * IndexPager with a formatted navigation bar
 319  */
 320 abstract class ReverseChronologicalPager extends IndexPager {
 321         public $mDefaultDirection = true;
 322
 323         function __construct() {
 324                 parent::__construct();
 325         }
 326
 327         function getNavigationBar() {
 328                 global $wgLang;
 329
 330                 if ( isset( $this->mNavigationBar ) ) {
 331                         return $this->mNavigationBar;
 332                 }
 333                 if ( !$this->mQueryDone ) {
 334                         $this->doQuery();
 335                 }
 336
 337                 # Don't announce the limit everywhere if it's the default
 338                 $urlLimit = $this->mLimit == $this->mDefaultLimit ? '' : $this->mLimit;
 339
 340                 if ( $this->mIsFirst ) {
 341                         $prevText = wfMsgHtml("prevn", $this->mLimit);
 342                         $latestText = wfMsgHtml('histlast');
 343                 } else {
 344                         $prevText = $this->makeLink( wfMsgHtml("prevn", $this->mLimit),
 345                                 array( 'dir' => 'prev', 'offset' => $this->mFirstShown, 'limit' => $urlLimit ) );
 346                         $latestText = $this->makeLink( wfMsgHtml('histlast'),
 347                                 array( 'limit' => $urlLimit ) );
 348                 }
 349                 if ( $this->mIsLast ) {
 350                         $nextText = wfMsgHtml( 'nextn', $this->mLimit);
 351                         $earliestText = wfMsgHtml( 'histfirst' );
 352                 } else {
 353                         $nextText = $this->makeLink( wfMsgHtml( 'nextn', $this->mLimit ),
 354                                 array( 'offset' => $this->mLastShown, 'limit' => $urlLimit ) );
 355                         $earliestText = $this->makeLink( wfMsgHtml( 'histfirst' ),
 356                                 array( 'dir' => 'prev', 'limit' => $urlLimit ) );
 357                 }
 358                 $limits = '';
 359                 foreach ( $this->mLimitsShown as $limit ) {
 360                         if ( $limits !== '' ) {
 361                                 $limits .= ' | ';
 362                         }
 363                         if ( $this->mIsBackwards ) {
 364                                 $offset = $this->mPastTheEndIndex;
 365                         } else {
 366                                 $offset = $this->mOffset;
 367                         }
 368                         $limits .= $this->makeLink( $wgLang->formatNum($limit),
 369                                 array('offset' => $offset, 'limit' => $limit ) );
 370
 371                 }
 372
 373                 $this->mNavigationBar = "($latestText | $earliestText) " . wfMsgHtml("viewprevnext", $prevText, $nextText, $limits);
 374                 return $this->mNavigationBar;
 375         }
 376 }
 377
 378 ?>