getNextOrderNumber.php

<php

class NameClass {
    /**
     * Genera numero secuencial de solicitud
     */
    public function getNextOrderNumber()
    {
        // Get the last created order
        $lastOrder = TuModelo::orderBy('created_at', 'desc')->first();

        if (!$lastOrder)
            // We get here if there is no order at all
            // If there is no number set it to 0, which will be 1 at the end.
            $number = 0;
        else
            $number = substr($lastOrder->nunfactura, 3);
        // If we have SOL0000001 in the database then we only want the number
        // So the substr returns this 0000001

        // Add the string in front and higher up the number.
        // the %07d part makes sure that there are always 7 numbers in the string.
        // so it adds the missing zero's when needed.

        return 'SOL' . sprintf('%07d', intval($number) + 1);
    }
}