code: async def start_transaction(connection_name: Optional[str] = None) -> BaseTransactionWrapper:
      
      connection = _get_connection(connection_name)
      transaction = connection._in_transaction()
      await transaction.start()
      return transaction
docs: Function to manually control your transaction.
  
      Returns transaction object with ``.rollback()`` and ``.commit()`` methods.
      All db calls in same coroutine context will run into transaction
      before ending transaction with above methods.
  
      :param connection_name: name of connection to run with, optional if you have only
                              one db connection