private function parentIs($conjunction, ModelId $parentModelId)
    {
        if (!empty($this->expression)) {
            $this->expression[] = $conjunction;
        }

        $index              = \count($this->variables);
        $this->expression[] = \sprintf(self::PARENT_IS_EXPRESSION, $index);
        $this->variables[]  = $parentModelId;
        $this->compiled     = null;

        return $this;
    }