code: def get_data_file_attachment(self, identifier, resource_id):
          
          # Get model run to ensure that it exists. If not return None
          model_run = self.get_object(identifier)
          if model_run is None:
              return None, None
          # Ensure that attachment with given resource identifier exists.
          if not resource_id in model_run.attachments:
              return None, None
          # Raise an exception if the attached resource is not a data file
          attachment = model_run.attachments[resource_id]
          filename = os.path.join(model_run.attachment_directory, resource_id)
          return filename, attachment.mime_type
docs: Get path to attached data file with given resource identifer. If no
          data file with given id exists the result will be None.
  
          Raise ValueError if an image archive with the given resource identifier
          is attached to the model run instead of a data file.
  
          Parameters
          ----------
          identifier : string
              Unique model run identifier
          resource_id : string
              Unique attachment identifier
  
          Returns
          -------
          string, string
              Path to attached data file on disk and attachments MIME type