How to get parent node from a attachment in drupal8 search api results

Question

I have apachesolr index search with Search API attachments. In the results I get a link to the file but I would like to get a link to the parent node. I tried in the view but there is no such field with relationship to file usage. I wrote the following in a module to override the field fid in the view but it returns an error

function hook_preprocess_views_view_field(&$variables) {
$view = $variables['view'];
$field = $variables['field'];
    if ($view->storage->id() == 'saa' &&
    $view->current_display == 'page_1' &&
    $field->field == 'fid') {
        $fid =  $variables['output']; 
        $file = \Drupal\file\Entity\File::load($fid);
        $file_usage = \Drupal::service('file.usage')->listUsage($file);
        $variables['results'] = $file_usage;
    }
}

It returns

The website encountered an unexpected error. Please try again later. TypeError: Argument 1 passed to Drupal\file\FileUsage\DatabaseFileUsageBackend::listUsage() must implement interface Drupal\file\FileInterface, null given, called in /home/rebecca/public_html/new5/modules/pdf_app/pdf_app.module on line 262 in Drupal\file\FileUsage\DatabaseFileUsageBackend->listUsage() (line 123 of core/modules/file/src/FileUsage/DatabaseFileUsageBackend.php).

Answer 1

$file should be instance of Drupal\file\FileInterface but in this case $file is null so you should check first on $file something

function hook_preprocess_views_view_field(&$variables) {
  $view = $variables['view'];
  $field = $variables['field'];
  if ($view->storage->id() == 'saa' &&
    $view->current_display == 'page_1' &&
    $field->field == 'fid') {
    $fid = $variables['output']->__toString();
    $file = \Drupal\file\Entity\File::load($fid);
    if ($file && $file instanceof Drupal\file\FileInterface) {
      $file_usage = \Drupal::service('file.usage')->listUsage($file);
      $variables['output'] = $file_usage;
    }
  }
}

Answer 2

Thanks to the help I got I manage to get it working

function hook_preprocess_views_view_field(&$variables) {
 $view = $variables['view'];
$field = $variables['field'];
if ($view->storage->id() == 'saa' &&
$view->current_display == 'page_1' &&
$field->field == 'fid') {
$fid = $variables['output']; 
if (!is_string($fid)){ 
$fid = $variables['output']->__toString();
}

$file = \Drupal\file\Entity\File::load($fid);
if ($file && $file instanceof Drupal\file\FileInterface) {
  $file_usage = \Drupal::service('file.usage')->listUsage($file);
  //var_dump($file_usage);
 if (array_key_exists("node",$file_usage['file'])){
  $essai = $file_usage['file']['node'];
}
 elseif (array_key_exists("media",$file_usage['file'])){
$essai = $file_usage['file']['media'];
}
  $news = (array_keys($essai));
  $new2 = (array_values($news));
  $nef = array_values($new2)[0];
  $event = \Drupal::entityTypeManager()->getStorage('node')->load($nef);
if (!$event)
 return false;

// add ->toString() or other if needed
$abs_link = $event->toLink(NULL, 'canonical', ['absolute' => true]);
  $variables['output'] = $abs_link;
  }
 }
}