I have a function like the following, used to get the total for a single invoice.

PROCEDURE GetInvoiceTotal()
This.SelectAlias("Invoice")
SUM Amount TO Total
RETURN Total

Now, I want to call GetInvoiceTotal() from a global object, and specify the invoice it should total. If I change the function to the one below,

PROCEDURE GetInvoiceTotal(InvoiceID)
This.GetInvoiceLines(InvoiceID)
This.SelectAlias("Invoice")
SUM Amount TO Total
RETURN Total

the problem is that GetInvoiceLines() by definition reloads the Invoice cursor, destroying any pending changes. This means I can't use it within the context of a single invoice anymore.

I need to be able to total an invoice in progress without losing changes, but I'd also like to be able to total a specified invoice at will. What's the easiest/best way to get the best of both worlds?

Chris.