I have a Drupal 7 submit method for updating CSV row by row to a custom table which I found under this link. I have tried to update it so that it works in Drupal 8 to no avail. How do I to modify it to work in Drupal 8?

function custom_module_submit($form, &$form_state) {      $file = $form_state['values']['csv_upload_file'];     $file->status = FILE_STATUS_PERMANENT;     $file->filename = str_replace(' ', '_', $file->filename);     file_save($file);      $csv_file = file_load($file->fid);     $file = fopen($csv_file->uri, "r");       while(! feof($file))     {         $customer = fgetcsv($file));         db_insert('your_db_table')             ->fields(array(                 'column1' => $customer[0],                 'column2' => $customer[1]             ))             ->execute();     }      fclose($file);      drupal_set_message('CSV data added to the database'); } 

The Drupal 8 code that I am trying to use is as below:

public function submitForm(array &$form, FormStateInterface $form_state) {     $file = $form_state->getValue('csv_upload');     $file->status = FILE_STATUS_PERMANENT;     $file->filename = str_replace(' ', '_', $file->filename);     file_save_data($file);      $csv_file = DrupalfileEntityFile::load($file->fid);     $file = fopen($csv_file->getFileUri(), "r");      while (!feof($file)) {         $customer = fgetcsv($file);         Drupal::database()->insert('your_db_table')             ->fields(array(                 'column1' => $customer[0],                 'column2' => $customer[1]             ))             ->execute();     }      fclose($file);      drupal_set_message('CSV data added to the database'); } 

Errors include:

1. Fatal error: Call to a member function getFileUri() on null in /home/annuities/public_html/modules/custom_module/src/Form/C‌​ustomForm.php on line 90.

Line 90: $file = fopen($csv_file->getFileUri(), "r");

2. Warning: Creating default object from empty value in Drupalcustom_moduleFormCustomForm->submitForm() (line 85 of modules/custom_module/src/Form/CustomForm.php).

Line 85: $file->status = FILE_STATUS_PERMANENT;

3. Notice: Undefined property: stdClass::$filename in Drupalcustom_moduleFormCustomForm->submitForm() (line 86 of modules/custom_module/src/Form/CustomForm.php).

Line 86: $file->filename = str_replace(' ', '_', $file->filename);

4. The file could not be created. Notice: Undefined property: stdClass::$fid in Drupalcustom_moduleFormCustomForm->submitForm() (line 89 of modules/custom_module/src/Form/CustomForm.php).

Line 89: $csv_file = DrupalfileEntityFile::load($file->fid);

5. Warning: array_flip(): Can only flip STRING and INTEGER values! in DrupalCoreEntityEntityStorageBase->loadMultiple() (line 227 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).

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