private function doValidateMinMax($rule, $key, $isValid)
    {
        $rule = explode(':', $rule);

        $method = Inflector::camelize($rule[0]);

        if (is_callable([$this, $method]) === false) {
            throw new \Exception('Undefined method '.__CLASS__.' '.$method.' called.');
        }

        if ($isValid === false) {
            $this->setErrors($key.self::ERROR, Inflector::camelize(str_replace('_', ' ', $key)));
        }

        return $this->$method($key, $rule[1]);
    }