def get_id_str(objects, delimiter='_'):
    """
    Get a string of sorted ids, separated by a delimiter.
    
    Args:
        objects (Model): An iterable of model instances.
    
    Keyword Args:
        delimiter (str): The string the ids will be joined on.
        
    Returns:
        str: The joined and sorted id string.
    """
    ids = [obj.id for obj in objects]
    ids.sort()
    ids = [str(identifier) for identifier in ids]
    id_str = delimiter.join(ids)
    return id_str