Validate: Only one row set to boolean at any time

Rails
1

How can I validate that only one of the rows in my database is true and
rest are false at any give time?

I’ve already figured out to do this except if I try to update the row
that is true. Then it fails.

Here’s the code: http://rafb.net/paste/results/Ryjnbq78.html

What needs to be done to make it work?

2

Uh, messed the subject line. It should say “true” instead of “boolean”
of course.

3

Another way I figured is:

validates_uniqueness_of :is_visitor

And then add a check: If is_visitor is true, validate, if it’s false,
then don’t. That would work perfectly but I don’t know how to access the
data being submitted for validation.

Ideas on how to do that?

4

Anyone have any ideas? I’m pretty stuck with this now.