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   1  <?php
   2  
   3  /**
   4   * Iterate over every object of a given type, without holding all of them in
   5   * memory. This is useful for performing database migrations.
   6   *
   7   *   $things = new LiskMigrationIterator(new LiskThing());
   8   *   foreach ($things as $thing) {
   9   *     // do something
  10   *   }
  11   *
  12   * NOTE: This only works on objects with a normal `id` column.
  13   *
  14   * @task storage
  15   */
  16  final class LiskMigrationIterator extends PhutilBufferedIterator {
  17  
  18    private $object;
  19    private $cursor;
  20    private $set;
  21  
  22    public function __construct(LiskDAO $object) {
  23      $this->set = new LiskDAOSet();
  24      $this->object = $object->putInSet($this->set);
  25    }
  26  
  27    protected function didRewind() {
  28      $this->cursor = 0;
  29    }
  30  
  31    public function key() {
  32      return $this->current()->getID();
  33    }
  34  
  35    protected function loadPage() {
  36      $this->set->clearSet();
  37  
  38      $results = $this->object->loadAllWhere(
  39        'id > %d ORDER BY id ASC LIMIT %d',
  40        $this->cursor,
  41        $this->getPageSize());
  42      if ($results) {
  43        $this->cursor = last($results)->getID();
  44      }
  45      return $results;
  46    }
  47  
  48  }