public function dbObject($field)
    {
        $fields = $this->compositeDatabaseFields();
        if (!isset($fields[$field])) {
            return null;
        }

        // Build nested field
        $key = $this->getName() . $field;
        $spec = $fields[$field];
        /** @var DBField $fieldObject */
        $fieldObject = Injector::inst()->create($spec, $key);
        $fieldObject->setValue($this->getField($field), null, false);
        return $fieldObject;
    }