isBaseField example

  protected function getSourceFieldOptions() {
    // If there are existing fields to choose from, allow the user to reuse one.     $options = [];
    foreach ($this->entityFieldManager->getFieldStorageDefinitions('media') as $field_name => $field) {
      $allowed_type = in_array($field->getType(), $this->pluginDefinition['allowed_field_types'], TRUE);
      if ($allowed_type && !$field->isBaseField()) {
        $options[$field_name] = $field->getLabel();
      }
    }
    return $options;
  }

  /** * {@inheritdoc} */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $options = $this->getSourceFieldOptions();
    

/** * Checks whether the given field can be stored in a shared table. * * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition * The field storage definition. * * @return bool * TRUE if the field can be stored in a shared table, FALSE otherwise. */
  public function allowsSharedTableStorage(FieldStorageDefinitionInterface $storage_definition) {
    return !$storage_definition->hasCustomStorage() && $storage_definition->isBaseField() && !$storage_definition->isMultiple() && !$storage_definition->isDeleted();
  }

  /** * Checks whether the given field has to be stored in a dedicated table. * * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition * The field storage definition. * * @return bool * TRUE if the field has to be stored in a dedicated table, FALSE otherwise. */