def _lookup_used_entity_id(self, file_details):
        """
        Return the file_version_id associated with the path from file_details.
        The file_version_id is looked up from a dictionary in the activity.
        :param file_details: dict: response from DukeDS POST to /files/
        :return: str: file_version_id uuid
        """
        # Since this uses the response from POST to /files/ this will include the ancestors and not be
        # effected by exclude_response_fields that were used when listing the project
        name_parts = [ancestor['name'] for ancestor in file_details['ancestors']
                      if ancestor['kind'] == KindType.folder_str]
        name_parts.append(file_details['name'])
        remote_path = os.sep.join(name_parts)
        return self.activity.remote_path_to_file_version_id[remote_path]