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