Small Select Bug Fix

I'm reminded that when ColdFusion 7 was released, it shipped with a small bug in the XForms implementation which caused multiple-select input elements to display with none selected if a user had previously selected multiple options. It had turned out to be something fairly simple, an oversight in their default XSL sheet and at the time I'd provided the fix for Jeff Small (although at the moment I can't find his blog entry where he posted it for everyone else -- send me the url if you have it and I'll post it here). I'm sure it was something the folks on the CF development team just hadn't antiscipated, after all how often do you use a multiple-select? (Of course, I say this expecting a quick response from the couple of folks who use them frequently.) :)

It's sort of come back to haunt me... In the previous versions of the onTap framework, I'd built in query-driven select input elements. The first iteration of these were unfortunately painfully slow. The problem at the time was that I was making it create a whole new html element structure for each option, instead of simply holding on to the query until display time. It turned out to be far too much overhead, and just as well most of the data in those structures was going unused anyway. So I then moved to the more logical approach of storing the query in the element structure for the select input and looping over them to create the options at time of display. This worked pretty well and even allowed me an easier way of fetching the current value of the select input by using the native ValueList() function. However, when setting the current value, I was still looping over each record in the query, like this:

<cfloop query="input.query">
<!--- get the value of the current option --->
<cfset thisvalue = input.query.inputvalue[currentrow] />
<!--- check to see if it's selected --->
<cfset isselected = ListFindNoCase(input.selected,thisvalue) />
<!--- reset the option selection --->
<cfset input.query.selected[currentrow] = iif(isselected,"thisvalue",de("")) />

You can see from this code how I can then use ValueList(input.query.inputvalue) to fetch the list of currently selected options. Well this was great, and then shortly after I started working on version 3.0 of the framework I realized that there may be an even more efficient way. Instead of looping over the query one record at a time, I could set the entire query all at once and it could potentially be much more efficient. Something like this:

<!--- reset all the options --->
<cfset ArraySet(input.query["selected"],"",1,input.query.recordcount) />
<!--- get the indexes of the selected options --->
<cfset selected = getSelectedIndexes(input.query,input.selected) />
<!--- set the selected flag for selected options --->
<cfloop index="i" list="#selected#">
<cfset input.query.selected[i] = input.query.inputvalue[i] />

So in this case the loop only processes one iteration for each selected option, instead of for each record in the query. In some cases where there are a lot of options in the list this can be much more efficient. I tested this after I implemented it and it is much more efficient when the select list is excessively large: hundreds of options or more, which may not be the best idea in the first place, but that's another blog. For most uses though, the efficiency probably won't change much from the last version.

The problem lies in that getSelectedIndexes() function (which is a simplification for the sake of the blog -- suffice to say that it creates a list of query indexes that should be selected without looping over the query). The algorithm I had for determining which query indexes were selected turned out to have a minor flaw in it and so where I had a query containing the values "en,en_CA,en_US" (and a few others), it was selecting all options beginning with "en", so the options for CA and US were being additionally selected when only "en" should have been. Of course I fixed this yesterday and uploaded a new build of the framework core code a few minutes ago.

I will give one caveat and that's the form tools do assume that you won't have any linefeed characters (ASCII char(10)) in your option values. So if for some reason you need that particular character in your data, you'll have to replace them with something else before displaying the form and after submitting it. Probably most people won't have any issues with that, since the inputvalue column will usually contain either integers, UUID strings or some other equivalent. Speaking of which, this is probably why I didn't catch this sooner, because I tend not to use autonumber / identity columns (though they're better supported now), and since most of my select elements contain a UUID equivalent, the values generally don't offer that kind of overlap.

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