ThemeSettings.php

<?php

namespace Drupal\system\Plugin\migrate\source\d7;

use Drupal\migrate_drupal\Plugin\migrate\source\VariableMultiRow;

/**
 * Drupal 7 theme settings source from database.
 *
 * For available configuration keys, refer to the parent classes.
 *
 * @see \Drupal\migrate_drupal\Plugin\migrate\source\VariableMultiRow
 * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
 * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
 *
 * @MigrateSource(
 *   id = "d7_theme_settings",
 *   source_module = "system"
 * )
 */
class ThemeSettings extends VariableMultiRow {
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        return $this->select('variable', 'v')
            ->fields('v', [
            'name',
            'value',
        ])
            ->condition('name', 'theme_%_settings', 'LIKE');
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        return [
            'name' => $this->t('Theme settings variable for a theme.'),
            'value' => $this->t('The theme settings variable value.'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['name']['type'] = 'string';
        return $ids;
    }

}