def pymongo_formatter(credentials):
    """Returns a DSN for a pymongo-MongoDB connection.

    Note that the username and password will still be needed separately in the constructor.

    Args:
        credentials (dict):
            The credentials dictionary from the relationships.

    Returns:
        (string) A formatted pymongo DSN.

    """
    return '{0}:{1}/{2}'.format(
        credentials['host'],
        credentials['port'],
        credentials['path']
    )