public function getAdapter()
    {
        if (is_null($this->adapter) || ! $this->adapter instanceof AdapterInterface) {
            $class = '\\Wslim\\Db\Adapter\\' . $this->options['adapter'] . 'Adapter';
            if (!class_exists($class)) {
                throw new DbException('database adapter is not exists:' . $class);
            }
            
            $this->adapter  =   new $class($this->options);
        }
        
        return $this->adapter;
    }