Is it possible to link automatically (via a function) fields in two tables that contain the same text?

I'm a bit mystified.  This code compiles with no errors but doesn't work:

let ShipsLogRecordID := Id;
let StartDate := 'Log Start Date';
let EndDate := 'Log End Date';
for DeckLogRec in (select DeckLog)["Log Date" >= StartDate and "Log Date" <= EndDate] do
    DeckLogRec.(ShipsLogRef := ShipsLogRecordID)
end

The code is on a record level button in a table called ShipsLog.  The ShipsLog record has fields to specify a date range.  For every record in the DeckLog that falls within the date range specified by the fields in the ShipsLog, the code should set the ShipsLogRef (a reference field in the DeckLog) to link to the ShipsLog.  It doesn't seem to do anything.  What am I doing wrong?