Feed::baseFieldDefinitions

public static Feed::baseFieldDefinitions(EntityTypeInterface $entity_type)

$fields['name'] = BaseFieldDefinition::create('string')
  ->setLabel(t('Name'));

public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
  /** @var \Drupal\Core\Field\BaseFieldDefinition[] $fields */
  $fields = parent::baseFieldDefinitions($entity_type);

  $fields['fid']->setLabel(t('Feed ID'))
    ->setDescription(t('The ID of the aggregator feed.'));

  $fields['uuid']->setDescription(t('The aggregator feed UUID.'));

  $fields['langcode']->setLabel(t('Language code'))
    ->setDescription(t('The feed language code.'));

  $fields['title'] = BaseFieldDefinition::create('string')
    ->setLabel(t('Title'))
    ->setDescription(t('The name of the feed (or the name of the website providing the feed).'))
    ->setRequired(TRUE)
    ->setSetting('max_length', 255)
    ->setDisplayOptions('form', array(
      'type' => 'string_textfield',
      'weight' => -5,
    ))
    ->setDisplayConfigurable('form', TRUE)
    ->addConstraint('FeedTitle');

  $fields['url'] = BaseFieldDefinition::create('uri')
    ->setLabel(t('URL'))
    ->setDescription(t('The fully-qualified URL of the feed.'))
    ->setRequired(TRUE)
    ->setDisplayOptions('form', array(
      'type' => 'uri',
      'weight' => -3,
    ))
    ->setDisplayConfigurable('form', TRUE)
    ->addConstraint('FeedUrl');

  $intervals = array(900, 1800, 3600, 7200, 10800, 21600, 32400, 43200, 64800, 86400, 172800, 259200, 604800, 1209600, 2419200);
  $period = array_map(array(\Drupal::service('date.formatter'), 'formatInterval'), array_combine($intervals, $intervals));
  $period[AGGREGATOR_CLEAR_NEVER] = t('Never');

  $fields['refresh'] = BaseFieldDefinition::create('list_integer')
    ->setLabel(t('Update interval'))
    ->setDescription(t('The length of time between feed updates. Requires a correctly configured cron maintenance task.'))
    ->setSetting('unsigned', TRUE)
    ->setRequired(TRUE)
    ->setSetting('allowed_values', $period)
    ->setDisplayOptions('form', array(
      'type' => 'options_select',
      'weight' => -2,
    ))
    ->setDisplayConfigurable('form', TRUE);

  $fields['checked'] = BaseFieldDefinition::create('timestamp')
    ->setLabel(t('Checked'))
    ->setDescription(t('Last time feed was checked for new items, as Unix timestamp.'))
    ->setDefaultValue(0)
    ->setDisplayOptions('view', array(
      'label' => 'inline',
      'type' => 'timestamp_ago',
      'weight' => 1,
    ))
    ->setDisplayConfigurable('view', TRUE);

  $fields['queued'] = BaseFieldDefinition::create('timestamp')
    ->setLabel(t('Queued'))
    ->setDescription(t('Time when this feed was queued for refresh, 0 if not queued.'))
    ->setDefaultValue(0);

  $fields['link'] = BaseFieldDefinition::create('uri')
    ->setLabel(t('URL'))
    ->setDescription(t('The link of the feed.'))
    ->setDisplayOptions('view', array(
      'label' => 'inline',
      'weight' => 4,
    ))
    ->setDisplayConfigurable('view', TRUE);

  $fields['description'] = BaseFieldDefinition::create('string_long')
    ->setLabel(t('Description'))
    ->setDescription(t("The parent website's description that comes from the @description element in the feed.", array('@description' => '<description>')));

  $fields['image'] = BaseFieldDefinition::create('uri')
    ->setLabel(t('Image'))
    ->setDescription(t('An image representing the feed.'));

  $fields['hash'] = BaseFieldDefinition::create('string')
    ->setLabel(t('Hash'))
    ->setSetting('is_ascii', TRUE)
    ->setDescription(t('Calculated hash of the feed data, used for validating cache.'));

  $fields['etag'] = BaseFieldDefinition::create('string')
    ->setLabel(t('Etag'))
    ->setDescription(t('Entity tag HTTP response header, used for validating cache.'));

  // This is updated by the fetcher and not when the feed is saved, therefore
  // it's a timestamp and not a changed field.
  $fields['modified'] = BaseFieldDefinition::create('timestamp')
    ->setLabel(t('Modified'))
    ->setDescription(t('When the feed was last modified, as a Unix timestamp.'));

  return $fields;
}