Generating a unique ID to pass to Payment Provider?

Question

Hi.
I have a site that has "orders" from customers which have a
unique ID (PK).
I'm using ASP / SQL.
I was passing this ID to my payment service provider but have
discovered
that, if a customer for some reason cancels the order (highly
likely), then
that ID cannot be passed to the payment provider again.
Therefore, when the
customer logs back in to our site, they'll still see the
order as "requiring
payment" but when they try to re-submit the order, the
payment provider
won't allow it! Groan!
Anyway, that is the way their system works, and I understand
why I suppose
(unique identifier 'an all that).
So, my solution is to simply pass a unique value (which
doesn't have to
relate to my unique order ID) to the payment provider.
My question is....how can I create/generate a unique value on
my checkout
page and ensure that the same value is never generated twice?
Is there a
feature in DW?
Oh yes, and I need it to be a numerical value! :o)
Thanks.
Nath.
Brain < Pea

Answer 1

Here is a guaranteed unique algorithm for any string (sequence of characters.)
   String createMyId(String stringToEncode)
      String uniqueId = stringOfChars;
      return uniqueId;
   }The code above guarantees the following properties (expressed as psuedo logic code, not java code.)
For any given sequence of chars A and B.
If A = B is true if and only if createMyId(A) = createMyId(B)
And of course
If A != B is true if and only if createMyId(A) != createMyId(B)
Of course the problem with the above algorithm is that it produces a variable sized value. But if you use a char array of of size Integer.MAX_VALUE then you can guarantee that it will work for any String in java. There is still a downside to this in that it requires a lot of data.
Of course someone who is particularily observant might note that this suggests that one might as well just store the string. That however is just an optimization in the above algorithm and as nothing to do with the validity of the algorithm itself.