_preQuery example

$this->initQuery();

    // Call a module hook and see if it wants to present us with a     // pre-built query or instruct us not to build the query for     // some reason.     // @todo: Implement this. Use the same mechanism Panels uses.
    // Run through our handlers and ensure they have necessary information.     $this->initHandlers();

    // Let the handlers interact with each other if they really want.     $this->_preQuery();

    if ($this->display_handler->usesExposed()) {
      /** @var \Drupal\views\Plugin\views\exposed_form\ExposedFormPluginInterface $exposed_form */
      $exposed_form = $this->display_handler->getPlugin('exposed_form');
      $this->exposed_widgets = $exposed_form->renderExposedForm();
      if (!empty($this->build_info['abort'])) {
        $this->built = TRUE;
        // Don't execute the query, $form_state, but rendering will still be executed to display the empty text.         $this->executed = TRUE;
        return empty($this->build_info['fail']);
      }
    }