code: public function getDriverName()
      {
          if ($this->_driverName === null) {
              if (($pos = strpos($this->dsn, ':')) !== false) {
                  $this->_driverName = strtolower(substr($this->dsn, 0, $pos));
              } else {
                  $this->_driverName = strtolower($this->getSlavePdo()->getAttribute(PDO::ATTR_DRIVER_NAME));
              }
          }
  
          return $this->_driverName;
      }
docs: Returns the name of the DB driver. Based on the the current [[dsn]], in case it was not set explicitly
  by an end user.
  @return string name of the DB driver