Looking up data Online

Situatution

You may find yourself using large reference files to lookup choices using the search() function; or individual data items using the pulldata() function. If these files become large and they are updated often then you may experience the following issues:

  • Every time a user of fieldTask opens a form that uses the reference data then all of that data has to be loaded into memory which can be slow.
  • When the reference data is changed it has to be downloaded onto all the enumerator phones. So if the file was say 5 MB in size and you had 100 enumerators that would be 500MB of data downloading. This will become a major issue if the reference file is updated multiple times per day.

Solution

Use online search and lookup:

search()  =>  lookup_choices()
pulldata()  =>  lookup()

You just need to change the function name, the parameters can remain the same. However lookup_choices has some extensions and can do more than search()

lookup_choices extensions

This is available with Smap Server version 20.09.

In addition to the parameters available with search() (Looking up Data), you can use ‘eval’ to evaluate an expression:

lookup_choices('linked_s10_231', 'eval', '#{q4} > now()')

In the above example all choices in the survey with the ident ‘linked_s_231’ where q4 is a date in the future are returned.

Note

What’s with the #{q4} instead of ${q4}? The #{question name} means to get the question in the survey that is being looked up. If you use ${question name} then the question is assumed to be in the survey that the user is filling in.

An example using both ${} and #{}:

lookup_choices('linked_s10_231', 'eval', '#{end_date} < ${project_date}')

in the above example choices are rturned where the end_date question in the looked up survey has a date earlier than the answer to the project_date question.

Comments

  1. There is a minor delay when looking up the data however overall performance should be faster as all the data does not need to be loaded when the form is opened.
  2. The enumerator has to be online and will need a data sim in the phone

This solution will suit a dynamic survey with large reference files that are constantly being updated and that is conducted in an areas with a mobile data network.

If your project requires work to be done offline then you should design is so that updates to the reference data are not too frequent and are managed to minimise the impact of downloading the data. For example you could schedule updates to the reference data when the data collectors are all at the base location with good wifi.