Most field types, allow the option for must be unique so the table would accept another record with that same value in that field (such as record Id)
In my use case if a facility exists in the onboarding table I do not want to allow that facility another record in the onboarding table – hence, as I understand, the “connected field” Must be unique
You can check for uniqueness using validation rules in a form component. Is that what you’re looking for?
Thanks @tim.young, I’m honestly not sure I knew about that and that validation
“Facility is not unique” does work in the for – in my use case I was using an action button on the table from the parent page to create the new record - and there doesn’t seem to be any such condition in the action button.
p.s. even though we’ve selected to “insert a new record” in the action rule we can still only set conditions based on the fields on the “current record”
But, thank you – this is another great possibility.
Glad that helped! Validation Rules exist for Form Components only so you will not find them anywhere else.
I do think the idea of having field level uniqueness is interesting though so I’m going to leave this open for future review 
Another option would be to have a rollup on the facilities table that counts the amount of connected onboarding records and use that value to see if another onboarding record can be created. How you implement this would depend on how the onboarding records are created.
