public function getSearchProperties()
    {
        static $props;
        if (null !== $props) {
            return $props;
        }

        $props = [];
        foreach ($this->getProperties() as $key => $property) {
            if (false === $property->isSearchProperty()) {
                continue;
            }
            $props[$key] = $property;
        }
        return $props;
    }