public function getOperation()
    {
        $direction = $this->getDirection();
        if ($direction === null) {
            return new DummyOperation();
        }
        if ($this->root !== null) {
            /** @var Grid $root */
            $root = $this->root;
            $fieldName = $root->getColumn($this->columnId)->getDataFieldName();
        } else {
            $fieldName = $this->columnId;
        }
        return new SortOperation($fieldName, $direction);
    }