Meaning of underscore( _ ) in a!pickerFieldCustom Component

RE: Meaning of underscore( _ ) in a!pickerFieldCustom Component

Chris — Thu, 07 Jul 2022 16:54:47 GMT

I would suggest to start a new thread with your issue as it is a bit different, and this thread is almost a year old.

Otherwise before doing so l would recommend to:

- Update your with() function as it has been superseded by a!localVariables()

- reduce the if() statement to if(len(ri!filter)<2.., as len() operates successfully on null or empty values

RE: Meaning of underscore( _ ) in a!pickerFieldCustom Component

pallavin0001 — Thu, 07 Jul 2022 16:38:12 GMT

Hi ,

I am trying achieve the same with above with extra requirement. Control the length of the search from the picker. If the length of the filter less than 2 (len(ri!filter)<2) i am trying not to query from the queryentity.Can u please Help me with this.I am getting below.Invalid index: Cannot index property 'data' of type String into type List of Variant after adding condition to the rule to fetch the data for picker component.

if(or(rule!APN_isBlank(ri!filter),and(not(rule!APN_isBlank(ri!filter)),len(ri!filter<2))),
{},
with(
local!output: a!queryEntity(
--filters to apply based on search
).data,
    local!matches: union(local!output, local!output),
    a!dataSubset(
      data: index(
        local!matches,
        ri!pickerDisplay,
        {}
      ),
      identifiers: index(
        local!matches,
        ri!identifier,
        {}
      )
    )
  )
))

RE: Meaning of underscore( _ ) in a!pickerFieldCustom Component

Spacetour — Wed, 13 Oct 2021 01:52:50 GMT

Thank you for the reply. It helped me understand.

RE: Meaning of underscore( _ ) in a!pickerFieldCustom Component

Peter Lewis — Tue, 12 Oct 2021 16:30:35 GMT

The technical term for the underscore is partial evaluation. It used to be something that was used pretty frequently in Appian. For example, the precursor to the a!forEach() function was called apply() and it often required using an underscore. However, with the introduction of newer functions, I believe this is the only place remaining that still uses an underscore.

Basically its purpose is that it allows you to evaluate the function without having that value defined yet. So if you add an underscore to the filter, it tells Appian that it doesn't need a value for that to render the component. However, once it does have a value for what the user typed in, this value will be inserted into the location where the underscore is provided and re-evaluated with the search text.

RE: Meaning of underscore( _ ) in a!pickerFieldCustom Component

Stefan Helzle — Tue, 12 Oct 2021 08:48:52 GMT

This will be the actual value at run-time. Check docs:

docs.appian.com/.../Expressions.html