book_admin/application/common/behavior/Polardb.php

<?php

namespace app\common\behavior;

use think\Config;

class Polardb
{

    public function run(&$request)
    {
        $adminPoladDb = Config::get('polardb.admin_hostname');
        if ($adminPoladDb) {
            Config::set('polardb.hostname', $adminPoladDb);
        }
    }
}