I followed the YouTube video to create a dere...

expressions
(G Man) #1

I followed the YouTube video to create a dereference table to link two databases and create a drop-down entry list. Everything works as expected. How can I stop my form from allowing the same data to be entered more than once? I want to avoid duplicate rows in my main table. Can I use a Valid_If

expression. I have tried

the expression =NOT(IN([_THIS],Table1[FirstLastName])).

(Praveen Seshadri (AppSheet)) #2

It sounds like you logically want a 1:1 references rather than a 1:N reference, right?

Yes you can use a Valid_If. If you set it up that way, it checks the value after the fact and will mark it as invalid.

Instead, you could do something like this for the Valld_If. You’re providing a list of values that effectively acts as the validity constraint.

Table2[KeyColumn] - Table1[RefColumn]

(replace the column names with the correct column names)

(G Man) #3

Praveen, thanks for your help. I’ve tried this but for some reason it’s not working for me - still getting duplicate rows. I’ll keep working on it. When I try =(IN([_THIS],Checkin Zone[_ComputedName]))=false it blocks duplicate entries but it also blocks any updates to the existing rows.