Unable to find column '_THISROW_BEFORE'

[LIUZheng]

I need better understanding of "_THISROW_BEFORE" and "_THISROW_AFTER". 

In my data table, I want to keep a record of the column with changes after the user save the form. I try to introduce an action in the Form Saved entry. But it doesn't work out. 

Column with change name "Status", column name for record "History". Expression as below:

CONCATENATE(
TEXT(NOW(),"dd/mm/yyyy HH:MM - "),
LOOKUP(USEREMAIL(),"Data_User","Email","_ShownName"), ":"
IF([_THISROW_BEFORE].[Status]<>[_THISROW_AFTER].[Status], CONCATENATE(" Status - ", [_THISROW_AFTER].[Status], ";"),""), "
", [History]
)

Where am I wrong?

[AleksiAlkio · Accepted solution]

"In my data table, I want to keep a record of the column with changes after the user save the form. I try to introduce an action in the Form Saved entry. But it doesn't work out. "

It doesn't work because after the form is saved, the before value is lost. Remember it's not saved to anywhere. When you open the form view, it remembers it. This pair of expressions were meant to work with automation Bots originally.. for example you can use them with the Event's condition rule.

[baba_sawane]

Hi LIUZheng,

Instead of using an action in the form saved entry, try with an automation with a data update trigger.

[LIUZheng]

@baba_sawane thank you for the advice.

I tried automation with data update trigger. The error doesn't pop up anymore, but the [_THISROW_AFTER].[Status] and [_THISROW_BEFORE].[Status] gives the same value, which is after update. So my "IF(before<>after,...)" doesn't work.

I finally succeeded by using ChangeCounter. I had ×10 columns needed to trace, and I created ×10 ChangeCounters for that, and it worked well.

I am still here without any  understanding to [_THISROW_BEFORE] and [_THISROW_AFTER]. Is there any helpful article?

[baba_sawane · Accepted solution]

https://support.google.com/appsheet/answer/11547057?hl=en

[LIUZheng]

thanks very much

[AleksiAlkio · Accepted solution]

"In my data table, I want to keep a record of the column with changes after the user save the form. I try to introduce an action in the Form Saved entry. But it doesn't work out. "

It doesn't work because after the form is saved, the before value is lost. Remember it's not saved to anywhere. When you open the form view, it remembers it. This pair of expressions were meant to work with automation Bots originally.. for example you can use them with the Event's condition rule.

[LIUZheng]

I tried in event condition, and it works. Thank you.