class ViewMode

class ViewMode extends ViewModeBase {
    
    /**
     * {@inheritdoc}
     */
    protected function initializeIterator() {
        $rows = [];
        $result = $this->prepareQuery()
            ->execute();
        while ($field_row = $result->fetchAssoc()) {
            $field_row['display_settings'] = unserialize($field_row['display_settings']);
            foreach ($this->getViewModes() as $view_mode) {
                // Append to the return value if the row has display settings for this
                // view mode and the view mode is neither hidden nor excluded.
                // @see \Drupal\field\Plugin\migrate\source\d6\FieldInstancePerViewMode::initializeIterator()
                if (isset($field_row['display_settings'][$view_mode]) && $field_row['display_settings'][$view_mode]['format'] != 'hidden' && empty($field_row['display_settings'][$view_mode]['exclude'])) {
                    if (!isset($rows[$view_mode])) {
                        $rows[$view_mode]['entity_type'] = 'node';
                        $rows[$view_mode]['view_mode'] = $view_mode;
                    }
                }
            }
        }
        return new \ArrayIterator($rows);
    }
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        $query = $this->select('content_node_field_instance', 'cnfi')
            ->fields('cnfi', [
            'display_settings',
        ]);
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        return [
            'display_settings' => $this->t('Serialize data with display settings.'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['view_mode']['type'] = 'string';
        return $ids;
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        $this->dependencies = parent::calculateDependencies();
        if (isset($this->configuration['constants']['targetEntityType'])) {
            $this->addDependency('module', $this->entityTypeManager
                ->getDefinition($this->configuration['constants']['targetEntityType'])
                ->getProvider());
        }
        return $this->dependencies;
    }

}