One way would be to create two calcs. On the parent side you can have a calc which will return something when the other field is empty.
Case ( IsEmpty ( Field1 ); "All"; Field1 )
Then on the child side, you would have another calc with your current key field concatenated in multi-line with the string "All".
List ( ChildsideCompany; "All" )
I wasnt sure if you were using IDs to match or not so I just left the name as a generic ChildsideCompany for this example.
Now change your filtered relationship to be based off those 2 new calc field.
I now have a calculated field on the contacts side with
(1 being the ID)
and the calculated field on the other side is being updated with "All" fine. But when it is set to "All" it still cannot find anything..
do I need to tell filemaker to look on the second line aswell?
Sorry if this isn't very clear,
Sorry, Had my calculation result as a number - that ALWAYS gets me muddled.
Thanks for your help!