"~{fieldName f}" -> case (fromPathPiece $ filterJsonMsg_value fjm) of 
                    (Just v) -> where_ $ defaultFilterOp (filterJsonMsg_comparison fjm) (~{vn} ~{projectField (ctxIsMaybe ctx vn)} ~{entityFieldTypeName e f}) ~{makeJust (boolToInt (fieldOptional f) + boolToInt (ctxIsMaybe ctx vn)) "(val v)"} 
                    _        -> return ()