Limit dropdown options in a child table based on condition in parent table

[HelloFOlks]

Hello,

For the following tables, I want to limit the dropdown options so that when a record in the parent table's Completed? = Yes, it is no longer shown in the dropdown for MO# in the Child table. 

Parent table: MO# , Completed?

Child table: RowID, MO#

*Primary keys in bold

*The MO# in the Child table is a REF of of MO# in the Parent. "Is a part of" is selected

Please, if you can, write out the Select function to be used in the ValidIf to achieve this. I have seen the support page for "Drop-down on a Ref column", but I am still not having luck. Thanks!

[Denny774]

Hey,

maybe:
Valid_If= NOT([MO#].[Completed?])

[HelloFOlks]

Hey thanks for getting back to me! I just tried this solution (I've also tried contains()), but instead of limiting the dropdown options, it just tells me the entry is invalid. I am hoping to not have it show as an option. I haven't had this issue with Valid_if  before.

[HelloFOlks · Accepted solution]

Ok, turns out there is a very simple solution (which of course took like 3 hours to figure out lol).

Valid_If = FILTER("Parent table", [Completed?] <> "Yes")

Thanks for the help!