public function addCondition($validation)
    {
        if (!$this->property) {
            throw new Exception\InvalidArgumentException(
                "Condition can be called only on properties!"
            );
        }
        $condition = new Validator\Condition(
            $this->_getValidation($validation),
            $this
        );
        $this->rules[] = $condition;
        return $condition->getValidator();
    }