class Field

class Field extends DrupalSqlBase {
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        $query = $this->select('content_node_field', 'cnf')
            ->fields('cnf', [
            'field_name',
            'type',
            'global_settings',
            'required',
            'multiple',
            'db_storage',
            'module',
            'db_columns',
            'active',
            'locked',
        ])
            ->distinct();
        // Only import fields which are actually being used.
        $query->innerJoin('content_node_field_instance', 'cnfi', '[cnfi].[field_name] = [cnf].[field_name]');
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        return [
            'field_name' => $this->t('Field name'),
            'type' => $this->t('Type (text, integer, ....)'),
            'widget_type' => $this->t('An instance-specific widget type'),
            'global_settings' => $this->t('Global settings. Shared with every field instance.'),
            'required' => $this->t('Required'),
            'multiple' => $this->t('Multiple'),
            'db_storage' => $this->t('DB storage'),
            'module' => $this->t('Module'),
            'db_columns' => $this->t('DB Columns'),
            'active' => $this->t('Active'),
            'locked' => $this->t('Locked'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareRow(Row $row) {
        // The instance widget_type helps determine what D8 field type we'll use.
        // Identify the distinct widget_types being used in D6.
        $widget_types = $this->select('content_node_field_instance', 'cnfi')
            ->fields('cnfi', [
            'widget_type',
        ])
            ->condition('field_name', $row->getSourceProperty('field_name'))
            ->distinct()
            ->orderBy('widget_type')
            ->execute()
            ->fetchCol();
        // Arbitrarily use the first widget_type - if there are multiples, let the
        // migrator know.
        $row->setSourceProperty('widget_type', $widget_types[0]);
        if (count($widget_types) > 1) {
            $this->migration
                ->getIdMap()
                ->saveMessage([
                'field_name' => $row->getSourceProperty('field_name'),
            ], $this->t('Widget types @types are used in Drupal 6 field instances: widget type @selected_type applied to the Drupal 8 base field', [
                '@types' => implode(', ', $widget_types),
                '@selected_type' => $widget_types[0],
            ]));
        }
        // Unserialize data.
        $global_settings = unserialize($row->getSourceProperty('global_settings'));
        $db_columns = $row->getSourceProperty('db_columns');
        $db_columns = is_string($db_columns) ? unserialize($db_columns) : FALSE;
        $row->setSourceProperty('global_settings', $global_settings);
        $row->setSourceProperty('db_columns', $db_columns);
        return parent::prepareRow($row);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['field_name'] = [
            'type' => 'string',
            'alias' => 'cnf',
        ];
        return $ids;
    }

}