code: def add_condition(self, field_name, op, value):
          
          if not isinstance(op, SQL_OP):
              if op not in SQL_OP.txt2op:
                  raise SQLOperatorInvalid(op)
              else:
                  op = SQL_OP.txt2op.get(op)
          self.conditions.append([field_name, op, value])
docs: Add a query condition and validate it.
          raise ParamsException if failed.
          self.view required
          :param field_name:
          :param op:
          :param value:
          :return: None