Trying to understand local/scoping of variables

Question

Hi: 
 I was experimenting with the Grid example in Appian Tutorials ( https://docs.appian.com/suite/help/23.1/Grid_Tutorial.html ) and noticed that I had some rows with no firstName and LastName. So, I thought I would use "fv!row.firstName" as part of the showWhen-attribute to prevent those rows from being show (see image below). However, I am getting "scoping error" messages. I know I can use query to filter out those rows but thought I would experiment with this approach because I have had issues with understanding local-variable scoping. For example, when I use {} right after a!localVariables (), I get scoping error (see second image. 
 Any responses to helping me understand local-variables/scoping would be appreciated. 
 Thank you. 
 Ma

Abhay Dalsaniya · Answer

It's simple. The variable is accessible within the block into which it is defined. 
 See the following to understand it better -

a!localVariables(
 local!a: 1,
 {
 a!localVariables(local!b: 2, local!a),
 local!b
 }
)

Abhay Dalsaniya · Answer

looks like fv!raw can only be used in the value parameter. Remove it from showWhen:a!isNotNullOrEmpty(fv!row.firstName) 
 Instead do following. 
 1. Define local variable (e.g. local!data) and capture the query result set into it. 
 2. Refer local!data into gridField -> data. 
 3. For showWhen condition Use local!data.firstName = <something>

Abhay Dalsaniya · Answer

Please try to understand the syntax of a!localVariables(). 
 a!localVariables ( localVar1, localVarN , expression ) 
 
 In your image2, you have defined local!productsList without using localVariable() which is violating the syntax because it is the expression portion. 
 use something like following. 
 a!localVariables(
 {
 a!localVariables(
 local!productList: rule!abc(),
 a!gridField()
 )
 }
) 
 
 See the color coding to understand it better.

Mike Schmitt · Answer

MaNa said: that would allow me to hide an entire row if one or more columns have is empty/null 
 You might want to think a bit more about this. Why would you want to hide a row when a column has an entirely empty/null value? What would this even look like / accomplish?

Mike Schmitt · Answer

Yes, if the requirement is that your form should show GPA and that the only rows which appear are those where it's non-blank, then the key is to filter your data in advance of feeding it into your grid. 
 If you're querying the data from the DB, then you would simply provide a query filter and filter out rows where that value is not populated. 
 If, on the other hand, you are passing the whole data set (with a mixture of rows) like as a process PV array, then you could instead create an on-form temp variable consisting only of the rows you'd like to display. Something along the lines of, local!myTemp Array: a!forEach(ri!myWholeArray, if(a!isNullOrEmpty(fv!item.GPA), {}, fv!item) within your local variables declaration. Then you'd simply pass that local variable into the data parameter of your grid, and you'd be displaying only the rows which have a value populated here.

Abhay Dalsaniya · Answer

MaNa said: As for the syntax in image 2, isn't the a!localVariable() on line 1, similar to the example in your response? 
 No it is not. The {} start the expression part and you cannot define local variable in the expression part directly the way you did it. To do that you need to have another nested localvariable() function, as I mentioned in my previous response. Hope this helps!

Trying to understand local/scoping of variables

Top Replies