Update:去掉多余代码

src/Driver/ConnBase.php

@@ -58,13 +58,12 @@ class ConnBase
                 $connection = $this->_connections['WRITE'] = $this->getWriteConnection();
 				break;
 		}
-        
+
         if(get_called_class() == 'Qii\Driver\Pdo\Connection'){
             $connection->setAttribute(\PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);
             $connection->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_WARNING);
             $connection->query('set names utf8');
         }
         return $connection;
-		throw new \Exception('Call undefined driver', __LINE__);
 	}
 }