This is more of a PSA post rather than a question, but I thought I'd put it up here to a) help anyone else out who is confused by this and b) hopefully get Appian's attention to fix this (I will also make a support case for this issue).
This is regarding how the XOR node in the process modeler evaluates multiple conditions. Looking at how the Decision tab is laid out (with IF...ELSE IF...ELSE IF labels and the ability to change the order of the conditions) my first thought would be that the conditions evaluate in order from top to bottom.
However, in the documentation for this node it states:
But then in other places the same page states:
The actual behavior of the XOR node indicates that the order of the conditions does not matter, all are evaluated simultaneously. I hope that Appian changes the behavior of the node to execute conditions in order as this would be much more useful.
If I have misunderstood anything in the documentation, please feel free to correct me, because as of now I don't really see any value to an XOR node when compared to an OR node.
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Yeah it's unfortunate that it doesn't work like "and()", where conditions that might throw an error can be safely "hidden" underneath prior checks against that condition. I've just accepted this as one of those foibles you need to get used to - i assume it's in their "process modeler quality of life common sense enhacements" back-lot dumpster.
It's actually done this way purposefully, so that if you have some expressions that take a while, we evaluate them in parallel.
that kinda makes sense I suppose - it's just unfortunate that we are thus forced to do some (sometimes unexpected and sometimes painful) bending-over-backwards to redundantly error-check in multiple subsequent evaluation conditions to prevent crashes. it seems like a little bit of try() trickery in the back-end could magic this away, in such a way that we only see errors generated when the row in question is actually reached(?!?)