@classmethod
def find_by_id(cls, obj_id, **kwargs):
    """ Finds a single object from this collection. """
    if isinstance(obj_id, str):
        obj_id = obj_id
    args = {'_id': obj_id}
    result = cls.collection().find_one(args, **kwargs)
    if result is not None:
        return cls(result, from_find=True)
    return None
