Lookups in input processing

[Mitch Theophila/MGT Computer Solutions]

hello all, 

although i've been coding fP for four years, i still get the occasional brain 
lockup when i'm working with the product.  with that preface, here is today's 
simple question.  apologies in advance if this has already been asked a few 
hundred times (which it probably has).

i've a client with a fairly traditional filepro app that they use for customer 
accounts receivable and other functions.

they would like an enhancement to their application as follows:  When they 
begin to enter a new invoice for a customer, they want to know if that customer 
has any open invoices outstanding, and be given the option to proceed (or not) 
with the new invoice.  They envision seeing this information in a prompt or 
message box that appears near the beginning of the new-invoice process, 
immediately after they specify which customer they are invoicing.  A y/n 
response would determine whether the new invoice should be created.

it's an easy lookup to write: the invoice record contains a field for 'balance 
due', which is decremented when payments are posted.  when the invoice is 
fully paid, the 'balance due' field goes to zero.  so all that the lookup 
logic would need do is look for records for a particular customer that had a 
nonzero balance due.

but if i were to add to their invoice file input processing a new lookup to 
examine other records in their invoice file, wouldn't such a lookup move the 
"current record pointer" away from the new record being created?  in such a 
case, wouldn't the data for the "new" invoice overwrite whatever record was 
currently "current"? 

perhaps fP handles this automatically, as it does so much else, but i'm 
familiar with lots of other database packages where it isn't .. in other 
words, i'm wondering whether fP requires the input process table to "remember 
the location" of the record being created, and "re-establish that location" 
when the changes are ready to be committed.

just askin' .. thanks in advance for any replies.   

.mitch theophila/MGT Computer Solutions