TITLE: Dynamic lists from user-added choices within repeats and
groups, in ODK
DATE: 2021-02-15
AUTHOR: John L. Godlee
====================================================================
For the tree data collection form I have been creating in ODK with
XLSForm, I wanted to allow users to quickly re-use species names
from previous species identified within the plot to cut down on
typing. It stands to reason that if a species is encountered within
a plot, there are likely other trees of the same species within the
plot. My mental model for the ODK form was to present the user with
a repeating question, one iteration for each individual, which
said: "from the choices listed below, choose the species of tree",
where the list of choices was populated by answers given by the
user during previous iterations. If the list didn't contain the
correct species the user could enter it manually in a question
below and the name would be added to the list of choices for future
iterations of the repeat. Currently XLSForm+pyxform lack a method
to accomplish this, so I posted a reply to a similar question on
the ODK support forums. I got an incredibly helpful response from a
member of the core developer team which involved editing the raw
xml after the form had been converted. Here is a rundown of the
method posted using an example where users are asked to record the
names of animals encountered. First, the .xls file, approximated
using a markdown table:
[similar question on the ODK support forums]:
https://forum.getodk.org/t/generate-multiple-choice-alternatives-bas
ed-on-the-answers-in-a-repeat/10269/16
type name label
choice_filter
required appearance relevance
calculation
--------------------------- ---------------
---------------------------------------------------------
------------------------------------------------------ ----------
-------------- ----------------------- -----------------
begin_repeat pet Pet
begin_group pet_group Pet
field-list
calculate pos
position(../..)
select_one ${animal_type} animal_select Select the animal
type. If not in the list, type below. position() !=
current()/../pos and animal_type != '' autocomplete
text animal_type Animal type
yes ${animal_select} =
''
end_group pet_group
end_repeat pet
Technically this file is invalid in its specification. It can be
awkward to produce XForm .xml from an invalid .xls. I used
xls2xform from pyxform:
xls2xform --pretty_print --skip_validate pets.xls pets.xml
pretty_print creates un-minified .xml that is easier to edit,
--skip_validate allows the .xml file to be produced, where
otherwise it would be discarded.
After the XML is created it is necessary to edit it. These are the
offending lines:
<itemset nodeset="..[position() != ./pos and animal_type !=
'']">
<value ref="animal_type"/>
<label ref="animal_type"/>
</itemset>
Which must be amended to:
<itemset nodeset="/data/pet[position() != current()/../pos and
pet_group/animal_type != '']">
<value ref="pet_group/animal_type"/>
<label ref="pet_group/animal_type"/>
</itemset>
This update basically changes the references to take into account
the nested grouping within the repeat, and changes where the pos
item updates from.
