'Check the existence of an object before an update or delete.
If the update or delete isn\'t applied, a LWTException is raised.'

def if_exists(self):

    if self.model._has_counter:
        raise IfExistsWithCounterColumn('if_exists    cannot    be    used    with    tables    containing    counter    columns')
    clone = copy.deepcopy(self)
    clone._if_exists = True
    return clone
