Question

I have develop this function which uses recursion to call itself. I need to generate a unique activation code.

It goes like this:
1. A random string is generated using the function in seperate class file. (See 2nd Code)
2. I am checking for uniqueness of that string in the activation table so that there are no duplicates.
3. In case if the random string is re-generated though I know that the chances are very less, but I dont want to take any chances. So I am checking it against the table records.

If the generated activated code is already there, then function should call itself again to generate a new activate code and the whole process goes on till we get a unique activation code which doesnt exist in the table records.

My question is that, Have I coded it correctly i.e. the recursion part. Please let me know if its not correct or if anybody has better or effective way to achieve this.

Note: I am calling these functions from a class file. Simply speaking I am using OOPs.
So I need to know the code to call the recursion should be

return generateUniqueActivationCode();

or

return $this->generateUniqueActivationCode();

Any help will be highly appreciated.

    // Generate Unique Activation Code
    //*********************************************************************************
    public function generateUniqueActivationCode()
    {
        $mysql = new Mysql();
        $string = new String();

        // This is coming from the 2nd part of code snippet that I have added
        $activation_code = $string->generateActivationCode();

        // Is Activation Code Unique Check
        $sql = "SELECT activation_id FROM ". TABLE_ACTIVATION_CODES ." WHERE activation_code='$activation_code' LIMIT 1";
        $query = $mysql->query($sql);

        if($mysql->rowCount($query) > 0)
        {
            // This function is calling itself recursively
            return generateUniqueActivationCode();
        }
        else
        {
            return $activation_code;
        }
    }

This is the code for generating Random Activation code

class String
{
    // Generates A Random String (Can be used for generating password etc.)
    //*********************************************************************************
    public function generateRandomString($noofchars=8)
    {
        $salt = "ABCDEFGHIJKLMNOPQRSTUVWXYZabchefghjkmnpqrstuvwxyz0123456789";
        srand((double)microtime()*1000000);
        $i = 0;
        while ($i <= $noofchars)
        {
            $num = rand() % 33;
            $tmp = substr($salt, $num, 1);
            $string = $string . $tmp;
            $i++;
        }
        return $string;
    }   
}
?>

Answer 1

I would have typed it like this:

public function generateUniqueActivationCode(){
        $mysql = new Mysql();
        $string = new String();
        do{
            $activation_code = $string->generateActivationCode();
            $sql = "SELECT activation_id FROM ". TABLE_ACTIVATION_CODES ." WHERE activation_code='$activation_code' LIMIT 1";
            $query = $mysql->query($sql);
        }while($mysql->rowCount($query) > 0);
        return $activation_code;
    }

Do (that runs ATLEAST one time), but repeats as long as your rowCount returns something bigger than 0.