Itemset from previous answers - select one from ${node}

[MartijnR]

Triggered by this question

It exposes the so-far-untapped XForm capability to create a choice list from previous answers (in a repeat).

It could have a wider implication by avoiding the more difficult indexed-repeat() or a combination of concat() and selected-at().

After discussion with @dorey we came up with the following initial syntax suggestion:

type	name	label	choice_filter
begin repeat	rep
text	name	Enter name
end repeat
select one from ${name}	choice	Choose	string-length(./name) > 0

<select1 ref="/data/choice">
   <label>Choose name</label>
   <itemset nodeset="/data/rep[string-length(./name) > 0]">
       <label ref="name"/>
       <value ref="name"/>
   </itemset>
</select1>

The ref attribute is the nodename of ${name} and the nodeset attribute is the parent of ${name} with an optional choice filter.

[MartijnR]

select multiple support might be difficult because we cannot allow spaces in the answers...

[dorey]

I like the idea of adding the ability to reference previous repeats. After thinking about the syntax a little more, I'm wondering if we could come up with a better way to specify it in the xlsform. Main reasons--

• select one from ${name} could require new regex changes for parsing the type field. Even if we went with select_one ${name} there's a high probability that parsers in pyxform and various xlsform form-builders and parsers () would need their regex fixed. And though we could do it on individual cases, it'd be cleaner if we could settle on a way of extending functionality that doesn't involve changing the regex.
• I vaguely remember people wanting to move away from { "type": "select_one listname" } towards something like { "type": "select_one", "list_name": "listname" }. Which would make parsing and validation of the form easier and more precise. (Note: I may have imagined this conversation)

How about:

type
select_one ${prev_name}

* still might need regex changes

or

type	list name
select_one	${prev_name}

[MartijnR]

I can see that would make sense from a developer perspective. Maybe move that discussion to a different issue, since it relates to all select type questions?

[ukanga]

I took the approach of using select one ${prev_name} in #381, it seemed the easiest way to implement without adding any additional syntax other than a reference to a previous field.

Any thoughts on the implementation?

[MartijnR]

Just happy thoughts about the feature from me and that test looks good.

[lognaturel]

@MartijnR you may want to check out @DavisRayM's progress at #472 and some of my comments to see whether you agree. I now see that in your initial example you weren't using ${} syntax in the choice_filter. Was that intentional? I initially thought it would be easier to let users use ${} but maybe it's reasonable to explain that fields within the target repeat are written as ./<field name>.

[MartijnR]

Thanks! I will do that. I believe that not using ${} syntax in the choice_filter was not intentional or maybe it was because pyxform wasn't producing relative paths at that time. Seems better to use the ${}syntax in examples (and support it).