public function getDefaultDbData()
    {
        $class = get_called_class();
        if (!isset(self::$cachedDefaultDbData[$class])) {
            self::$cachedDefaultDbData[$class] = [];
            foreach (array_keys(static::$dbProperties) as $propertyName) {
                self::$cachedDefaultDbData[$class][$propertyName] = $this->getDefaultDbPropertyValue($propertyName);
            }
        }

        return self::$cachedDefaultDbData[$class];
    }