Get fully-qualified parent path and prefix for this collection.

        Returns:
            Tuple[str, str]: Pair of

            * the fully-qualified (with database and project) path to the
              parent of this collection (will either be the database path
              or a document path).
            * the prefix to a document in this collection.

def _parent_info(self):
        """Get fully-qualified parent path and prefix for this collection.

        Returns:
            Tuple[str, str]: Pair of

            * the fully-qualified (with database and project) path to the
              parent of this collection (will either be the database path
              or a document path).
            * the prefix to a document in this collection.
        """
        parent_doc = self.parent
        if parent_doc is None:
            parent_path = _helpers.DOCUMENT_PATH_DELIMITER.join(
                (self._client._database_string, "documents")
            )
        else:
            parent_path = parent_doc._document_path

        expected_prefix = _helpers.DOCUMENT_PATH_DELIMITER.join((parent_path, self.id))
        return parent_path, expected_prefix