Creating an expression to Track the History of Another Column (List has Elements of Mismatched Types)

[jthurston]

Hello,

We have a CLASS column (Type=REF) that tracks which class a student is currently in. I want to create a CLASS HISTORY (Type=EnumList) column that will show a list of all previous values in the CLASS column, and the date of change. So for example, maybe the CLASS value is Smith.Lit101, and the CLASS History would say Smith.Lit101 8/23/21, Harris.Mth200 4/15/21, Piper.Phil101 3/12/20, etc.

I don’t think that the “Change” column types will work for this (right?). So I’m trying to create a bot. The trigger is set to occur when a change is made to the CLASS column. Here’s my attempt at the expression used in the process part of the bot:

SORT( [Class History] + LIST([Class], Today()) - LIST(""), TRUE)

So, begin with the current CLASS HISTORY value, then add another list item that contains the current value of the CLASS column + today’s date.

AppSheet won’t accept this formula, since it says the list has elements of mismatched types. I’m not exactly sure what the cause of the mismatch is, or how to get around it. Is there a way to tell AppSheet to allow mismatched elements? Or is there a better way to do this?

Thank you!