ChunkedIterator.php

<?php

/**
 * @file
 * Contains \Drupal\Core\Entity\EntityIterator.
 */

namespace Drupal\Core\Entity;

/**
 * Provides an Iterator class for dealing with large amounts of entities
 * but not loading them all into memory.
 */
class ChunkedIterator implements \IteratorAggregate, \Countable {

  /**
   * The entity storage controller to load entities.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $entityStorage;

  /**
   * An array of entity IDs to iterate over.
   *
   * @var array
   */
  protected $entityIds;

  /**
   * The size of each chunk of loaded entities.
   *
   * This will also be the amount of cached entities stored before clearing the
   * static cache.
   *
   * @var int
   */
  protected $chunkSize;

  /**
   * @var \Closure
   */
  protected $closure;

  /**
   * Constructs an entity iterator object.
   *
   * @param \Drupal\Core\Entity\EntityStorageInterface $entity_controller
   * @param array $ids
   * @param int $chunk_size
   */
  public function __construct(EntityStorageInterface $entity_storage_controller, array $ids, $chunk_size = 50) {
    // Create a clone of the storage controller so the static cache of the
    // actual storage controller remains intact.
    $this->entityStorage = clone $entity_storage_controller;
    // Make sure we don't use a keyed array.
    $this->entityIds = array_values($ids);
    $this->chunkSize = (int) $chunk_size;
  }

  /**
   * Implements \Countable::count().
   */
  public function count() {
    return count($this->entityIds);
  }

  /**
   * Implements \IteratorAggregate::GetIterator()
   */
  public function getIterator() {
    foreach (array_chunk($this->entityIds, $this->chunkSize) as $ids_chunk) {
      foreach ($this->loadEntities($ids_chunk) as $id => $entity) {
        yield $id => $entity;
      }
    }
  }

  /**
   * Loads a set of entities.
   *
   * This depends on the cacheLimit property.
   */
  protected function loadEntities(array $ids) {
    // Reset any previously loaded entities then load the current set of IDs.
    $this->resetCache();
    return $this->entityStorage->loadMultiple($ids);
  }

  /**
   * Resets the entity storage static cache.
   */
  protected function resetCache() {
    $closure = $this->getClosure();
    $closure();
  }

  /**
   * Gets the closure bound to the entity storage.
   *
   * @return \Closure
   */
  protected function getClosure() {
    if (!isset($this->closure)) {
      $this->closure = function () {
        $this->entities = [];
      };

      $this->closure->bindTo($this->entityStorage);
    }

    return $this->closure;
  }

}