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Strange cheque-reading code in form

September 30, 2010

This is just a story about a really weird bit of code. It was the type of code you look at and say, “that’s obviously wrong” and delete straight away.

One of the requirements was to rebuild an Oracle form, a data-entry form for receipts (cash, cheque, credit card, etc). Some of the cashiers use these cheque readers to read the numbers off the MICR band, and with the first release of the new form they reported a defect – “the cheque readers don’t work”.

I didn’t have access to a cheque reader when I was developing the form, but assumed that it would be a normal cheque reader – they put the cheque in, it reads it, it sends a series of digits to the computer. The form should work no different than if the operator keyed in the numbers manually (which they have to do, anyway, if the cheque reader doesn’t work for a particular cheque).

So to investigate the defect I requisitioned a cheque reader, along with some test cheques; after some difficulty (turns out these things don’t work alongside my USB keyboard, I had to get a PS2 keyboard), it was working.

It didn’t take long to discover that the cheque reader was sending the cheque number and BSB in the wrong order, as far as the form is concerned; thus why the validation was failing.

I opened up the old form again, and had a good hard look at the fields. Turns out, what I missed originally is that there is a custom KEY-NEXT-ITEM trigger on the bank code field (which is where the operator puts the focus before using the cheque reader). It looks something like this:

DECLARE
  v_data VARCHAR2(50) := REPLACE(REPLACE(:rct.bak_code
                         ,' ','')
                         ,CHR(9),'');
BEGIN
  IF LENGTH(v_data) > 4 THEN
    IF LENGTH(v_data) < 14 THEN
       NULL;
    ELSE
      :rct.cheque_no := SUBSTR(v_data,1,6);
      :rct.bak_code := SUBSTR(v_data,7,3);
      :rct.branch := SUBSTR(v_data,10,3);
      go_field('RCT.CHEQUE_TYPE');
    END IF;
  ELSE
    go_field('RCT.BRANCH');
  END IF;
END;

It turns out that:

(a) the REPLACE(REPLACE( code to remove spaces and tab characters (CHR(9)) is redundant, since the cheque reader never sends spaces, and when it sends a TAB, Oracle Forms doesn’t put a CHR(9) into the field anyway; instead it fires the KEY-NEXT-ITEM trigger

(b) if the length of the data is between 5 and 13, the KEY-NEXT-ITEM trigger does nothing; which means the focus stays in the bak_code field

It’s (b) that is the reason this worked. The trigger fires three times when the cheque reader is used; the third time the trigger fires, it’s got enough digits lumped together in the bak_code field, which it then splits apart, and moves the relevant bits to the cheque_no and branch fields.

A normal, sane person, building this form, would have designed the form to accept the cheque number, bank code and branch in the same order that they are read from the cheque reader; that way, no special code is required – the cheque reader just tabs through the fields, filling them in as it goes.

Oh well – it’s too late to do a screen redesign now, so I’ve had to pretty much replicate the same behaviour in the new form; except that my new code is a little bit smarter – it can also read money orders, which I’ve been told will make the cashiers very happy.

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