class DatabaseFileUsageBackend

file.module in drupal/core/modules/file/file.module

Defines a "managed_file" Form API field and a "file" field for Field module.

file.services.yml in drupal/core/modules/file/file.services.yml

drupal/core/modules/file/file.services.yml

file.usage in drupal/core/modules/file/file.services.yml

Drupal\file\FileUsage\DatabaseFileUsageBackend

class DatabaseFileUsageBackend extends FileUsageBase {

  /**
   * The database connection used to store file usage information.
   *
   * @var Drupal\Core\Database\Connection
   */
  protected $connection;

  /**
   * The name of the SQL table used to store file usage information.
   *
   * @var string
   */
  protected $tableName;

  /**
   * Construct the DatabaseFileUsageBackend.
   *
   * @param Drupal\Core\Database\Connection $connection
   *   The database connection which will be used to store the file usage
   *   information.
   * @param string $table
   *   (optional) The table to store file usage info. Defaults to 'file_usage'.
   */
  public function __construct(Connection $connection, $table = 'file_usage') {
    $this->connection = $connection;
    $this->tableName = $table;
  }

  /**
   * Implements Drupal\file\FileUsage\FileUsageInterface::add().
   */
  public function add(File $file, $module, $type, $id, $count = 1) {
    $this->connection
      ->merge($this->tableName)
      ->key(array(
      'fid' => $file->fid,
      'module' => $module,
      'type' => $type,
      'id' => $id,
    ))
      ->fields(array(
      'count' => $count,
    ))
      ->expression('count', 'count + :count', array(
      ':count' => $count,
    ))
      ->execute();
    parent::add($file, $module, $type, $id, $count);
  }

  /**
   * Implements Drupal\file\FileUsage\FileUsageInterface::delete().
   */
  public function delete(File $file, $module, $type = NULL, $id = NULL, $count = 1) {

    // Delete rows that have a exact or less value to prevent empty rows.
    $query = $this->connection
      ->delete($this->tableName)
      ->condition('module', $module)
      ->condition('fid', $file->fid);
    if ($type && $id) {
      $query
        ->condition('type', $type)
        ->condition('id', $id);
    }
    if ($count) {
      $query
        ->condition('count', $count, '<=');
    }
    $result = $query
      ->execute();

    // If the row has more than the specified count decrement it by that number.
    if (!$result && $count > 0) {
      $query = $this->connection
        ->update($this->tableName)
        ->condition('module', $module)
        ->condition('fid', $file->fid);
      if ($type && $id) {
        $query
          ->condition('type', $type)
          ->condition('id', $id);
      }
      $query
        ->expression('count', 'count - :count', array(
        ':count' => $count,
      ));
      $query
        ->execute();
    }
    parent::delete($file, $module, $type, $id, $count);
  }

  /**
   * Implements Drupal\file\FileUsage\FileUsageInterface::listUsage().
   */
  public function listUsage(File $file) {
    $result = $this->connection
      ->select($this->tableName, 'f')
      ->fields('f', array(
      'module',
      'type',
      'id',
      'count',
    ))
      ->condition('fid', $file->fid)
      ->condition('count', 0, '>')
      ->execute();
    $references = array();
    foreach ($result as $usage) {
      $references[$usage->module][$usage->type][$usage->id] = $usage->count;
    }
    return $references;
  }

}