class FieldInstancePerViewMode

class FieldInstancePerViewMode extends ViewModeBase {
    
    /**
     * {@inheritdoc}
     */
    protected function initializeIterator() {
        $rows = [];
        $result = $this->prepareQuery()
            ->execute();
        while ($field_row = $result->fetchAssoc()) {
            // These are added to every view mode row.
            $field_row['display_settings'] = unserialize($field_row['display_settings']);
            $field_row['widget_settings'] = unserialize($field_row['widget_settings']);
            $bundle = $field_row['type_name'];
            $field_name = $field_row['field_name'];
            foreach ($this->getViewModes() as $view_mode) {
                // Append to the return value if the row has display settings for this
                // view mode and the view mode is neither hidden nor excluded.
                // @see \Drupal\node\Plugin\migrate\source\d6\ViewMode::initializeIterator()
                if (isset($field_row['display_settings'][$view_mode]) && $field_row['display_settings'][$view_mode]['format'] != 'hidden' && empty($field_row['display_settings'][$view_mode]['exclude'])) {
                    $index = $view_mode . "." . $bundle . "." . $field_name;
                    $rows[$index]['entity_type'] = 'node';
                    $rows[$index]['view_mode'] = $view_mode;
                    $rows[$index]['type_name'] = $bundle;
                    $rows[$index]['field_name'] = $field_name;
                    $rows[$index]['type'] = $field_row['type'];
                    $rows[$index]['module'] = $field_row['module'];
                    $rows[$index]['weight'] = $field_row['weight'];
                    $rows[$index]['label'] = $field_row['display_settings']['label']['format'];
                    $rows[$index]['display_settings'] = $field_row['display_settings'][$view_mode];
                    $rows[$index]['widget_settings'] = $field_row['widget_settings'];
                }
            }
        }
        return new \ArrayIterator($rows);
    }
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        $query = $this->select('content_node_field_instance', 'cnfi')
            ->fields('cnfi', [
            'field_name',
            'type_name',
            'weight',
            'label',
            'display_settings',
            'widget_settings',
        ])
            ->fields('cnf', [
            'type',
            'module',
        ]);
        $query->join('content_node_field', 'cnf', '[cnfi].[field_name] = [cnf].[field_name]');
        $query->orderBy('cnfi.weight');
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        return [
            'field_name' => $this->t('The machine name of field.'),
            'type_name' => $this->t('Content type where this field is used.'),
            'weight' => $this->t('Weight.'),
            'label' => $this->t('A name to show.'),
            'widget_type' => $this->t('Widget type.'),
            'widget_settings' => $this->t('Serialize data with widget settings.'),
            'display_settings' => $this->t('Serialize data with display settings.'),
            'description' => $this->t('A description of field.'),
            'widget_module' => $this->t('Module that implements widget.'),
            'widget_active' => $this->t('Status of widget'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['type_name']['type'] = 'string';
        $ids['view_mode']['type'] = 'string';
        $ids['entity_type']['type'] = 'string';
        $ids['field_name']['type'] = 'string';
        return $ids;
    }

}