You can’t select and assign in the same line. You must first select the record you are trying to update, then update it. The code you provided is non-sense though…I’m completely lost at what you are trying to do.
select forupdate dupCust where dupCust.LineNum == (This is where you put the line number of the record you are trying to update);
I have no idea what you are trying to accomplish though.
You’re getting into infinite recursion, because the update() method always calls itself.
You don’t need any explicit update at all - simply set the value to this.LineNum above super() - the record is saved in super(). Also, you’ll probably want to use this.QtyOrdered and this.SalesPrice instead of your empty variables.