getByField example

  /** * {@inheritdoc} */
  public function flagWidgetsErrorsFromViolations(EntityConstraintViolationListInterface $violations, array &$form, FormStateInterface $form_state) {
    $entity = $violations->getEntity();
    foreach ($violations->getFieldNames() as $field_name) {
      // Only show violations for fields that actually appear in the form, and       // let the widget assign the violations to the correct form elements.       if ($widget = $this->getRenderer($field_name)) {
        $field_violations = $this->movePropertyPathViolationsRelativeToField($field_name, $violations->getByField($field_name));
        $widget->flagErrors($entity->get($field_name), $field_violations, $form, $form_state);
      }
    }
  }

  /** * Moves the property path to be relative to field level. * * @param string $field_name * The field name. * @param \Symfony\Component\Validator\ConstraintViolationListInterface $violations * The violations. * * @return \Symfony\Component\Validator\ConstraintViolationList * A new constraint violation list with the changed property path. */

return array_merge(['parent', 'weight'], parent::getEditedFieldNames($form_state));
  }

  /** * {@inheritdoc} */
  protected function flagViolations(EntityConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state) {
    // Manually flag violations of fields not handled by the form display. This     // is necessary as entity form displays only flag violations for fields     // contained in the display.     // @see ::form()     foreach ($violations->getByField('parent') as $violation) {
      $form_state->setErrorByName('parent', $violation->getMessage());
    }
    foreach ($violations->getByField('weight') as $violation) {
      $form_state->setErrorByName('weight', $violation->getMessage());
    }

    parent::flagViolations($violations, $form, $form_state);
  }

  /** * {@inheritdoc} */

$entity_violations = $violations->getEntityViolations();
    foreach ($entity_violations as $violation) {
      /** @var \Symfony\Component\Validator\ConstraintViolation $violation */
      $error['detail'] = 'Entity is not valid: '
        . $violation->getMessage();
      $error['source']['pointer'] = '/data';
      $errors[] = $error;
    }

    $entity = $violations->getEntity();
    foreach ($violations->getFieldNames() as $field_name) {
      $field_violations = $violations->getByField($field_name);
      $cardinality = $entity->get($field_name)
        ->getFieldDefinition()
        ->getFieldStorageDefinition()
        ->getCardinality();

      foreach ($field_violations as $violation) {
        /** @var \Symfony\Component\Validator\ConstraintViolation $violation */
        $error['detail'] = $violation->getPropertyPath() . ': '
          . PlainTextOutput::renderFromHtml($violation->getMessage());

        $pointer = '/data/attributes/'
          .

  protected function getEditedFieldNames(FormStateInterface $form_state) {
    return array_merge(['created', 'name'], parent::getEditedFieldNames($form_state));
  }

  /** * {@inheritdoc} */
  protected function flagViolations(EntityConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state) {
    // Manually flag violations of fields not handled by the form display.     foreach ($violations->getByField('created') as $violation) {
      $form_state->setErrorByName('date', $violation->getMessage());
    }
    foreach ($violations->getByField('name') as $violation) {
      $form_state->setErrorByName('name', $violation->getMessage());
    }
    parent::flagViolations($violations, $form, $form_state);
  }

  /** * Form submission handler for the 'preview' action. * * @param array $form * An associative array containing the structure of the form. * @param \Drupal\Core\Form\FormStateInterface $form_state * The current state of the form. */