Lightswitch lookup from unused values
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I have an lightswitch application that is used for value mapping. i have my target table and a view for source values, which i want to map together in target. I define two relations in LS to have my lookup fields (Value1, Value2) and do the rest of data manipulation when user selects the values from the list.

What I want to do next is to have an ability to show only unused values in lookup (when choosing Value1 and Value2). The values that are not chosen and not in target table. I can manage that with additional JOIN in my view, but then when I launch my application, older records have empty cells Value1, Value2 (because they get filtered out by JOIN).

and i could not figure out any other way to show only unused values in lookup (I can not modify source tables) or have lookup functionality without table relations (in that case I think that JOIN on View solution would work)