How to place an Auto-increment id in v3.1

[sharan1]

when we updated factory muffin from v2.1 to v3.1

For auto-incrementing ids, we used to use the following function:

function () {
        static $last;
         if ($last === null) {
             return $last = 1;
         }
         return ++$last;
}

But after upgrading the same function always started returning 1, resulting in errors for duplication of primary key in our test database.

Any idea what could be the issue and how to resolve it?

Originally posted by @sharan1 in #382 (comment)

[GrahamCampbell]

Thanks for the report. I can't quite remember why this would have been broken. I'll have a think. ;)