public function unique($id = null, $idClumn = null, $extra = null)
    {
        $id = $id ?: $this->model->id ?: 'NULL';
        $idClumn = $idClumn ?: $this->model->getKeyName();

        $parts = [
            "unique:{$this->model->getConnectionName()}.{$this->model->getTable()}",
            $this->db_name,
            $id,
            $idClumn
        ];

        if ($extra) {
            $parts []= trim($extra, ',');
        }

        $this->rule(join(',', $parts));

        return $this;
    }