UploadForm.php

<?php

namespace Drupal\mitacan\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

class MitacanUploadForm extends FormBase {
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['csv_upload'] = [
      '#type' => 'managed_file',
      '#title' => 'CSV dosyasını yükleyin',
      '#upload_validators' => [
        'file_validate_extensions' => ['csv'],
        'file_validate_size' => [25600000],
      ]
    ];
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => 'Yükle'
    ];
    return $form;
  }

  public function getFormId() {
    return 'mitacan.upload';
  }

  public function submitForm(array &$form, FormStateInterface $form_state) {
    $fids = $form_state->getValue('csv_upload', []);
    $files = \Drupal::entityTypeManager()->getStorage('file')->loadMultiple($fids);
    foreach ($files as $file) {
      $destination = $file->toArray()['uri'][0]['value'];
      $file = fopen($destination, "r");
      while (!feof($file)) {
        $b2bresim = fgetcsv($file);
        \Drupal::database()->insert('mitacan')
        ->fields(array(
          'images' => $b2bresim[0],
          'stokkodu' => $b2bresim[1],
          'stokadi' => $b2bresim[2],
          'stokkodugrup1' => $b2bresim[3],
          'stokadigrup1' => $b2bresim[4],
          'stokkodugrup2' => $b2bresim[5],
          'stokadigrup2' => $b2bresim[6],
          'stokkodugrup3' => $b2bresim[7],
          'stokadigrup3' => $b2bresim[8],
          'stokkodugrup4' => $b2bresim[9],
          'stokadigrup4' => $b2bresim[10],
          'listeno' => $b2bresim[11],
          'listeadi' => $b2bresim[12],
          'logolar' => $b2bresim[13]
        ))
        ->execute();
      }
      fclose($file);
      drupal_set_message('CSV data added to the database');
    }
  }
}