Mini Project: Simple Order List Subfile

What We Are Building

A subfile screen listing every order for one customer, combining SETLL/READE native file I/O with the subfile load-display pattern covered throughout the Subfiles lesson group.

Business Scenario

Extending the Customer Inquiry Program mini project, imagine that customer service representative now also needing to see a specific customer's full order history in one scrollable list, rather than just their current balance, before deciding how to help them.

Concepts Used

• SETLL and READE for reading every record sharing a key value, from the SETLL in RPGLE and READE for Reading Matching Keys lessons.
• The subfile record format and control record format pair, from the Subfile Record Format vs Subfile Control Record Format lesson.
• The clear-load-display pattern, from the Simple Inquiry Subfile Pattern lesson.

Files and Programs Involved

• ORDHIST, the existing order history file from the RPGLE File I/O lessons, keyed by CUSTNBR, holding ORDNBR, CUSTNBR, and ORDAMT.
• ORDSFLD, a new display file containing the subfile record format, ORDSFL (one row per order), and its control record format, ORDCTL.
• ORDLSTR, the RPGLE program tying ORDSFLD and ORDHIST together.

Step-by-Step Build Outline

1. Design ORDSFLD's ORDSFL subfile record format with fields for order number and amount, and ORDCTL as its control record format with SFLCTL(ORDSFL), exactly as covered in the Subfile Record Format vs Subfile Control Record Format lesson.
2. Prompt for a customer number using a small input screen, or accept it as a parameter for simplicity.
3. Clear the subfile: turn SFLCLR on and SFLDSP off, then show ORDCTL once, exactly as covered in the SFLDSP, SFLDSPCTL, and SFLCLR Explained lesson.
4. Use SETLL custNbr ORDHIST; followed by a READE loop, writing one ORDSFL record per matching order, exactly the pattern covered in the READE for Reading Matching Keys lesson.
5. Turn SFLDSP and SFLDSPCTL on, then exfmt ORDCTL to display the loaded list.

Example Code

dcl-f ORDSFLD workstn;
dcl-f ORDHIST disk keyed;

dcl-s custNbr packed(6:0);

custNbr = 1042;

*in30 = *on;
*in40 = *off;
write ORDCTL;

*in30 = *off;
setll custNbr ORDHIST;
reade custNbr ORDHIST;
dow not %eof(ORDHIST);
  write ORDSFL;

  reade custNbr ORDHIST;
enddo;

*in40 = *on;
*in41 = *on;
exfmt ORDCTL;

*inlr = *on;

This is the same clear-load-display shape covered in the Simple Inquiry Subfile Pattern lesson, now using real SETLL/READE file I/O instead of a fixed illustrative loop.

How to Test It

Test with a customer who has several orders, confirming every one appears in the subfile; a customer with exactly one order; and a customer with no orders at all, confirming the subfile displays as empty without producing an unexpected error.

Common Mistakes

• Forgetting SETLL before the READE loop, which leaves the file positioned incorrectly.
• Writing ORDCTL for the clear step with SFLDSP still on, which would attempt to display a subfile that has not been loaded yet.
• Using CHAIN instead of SETLL/READE, which would only ever load one order rather than every matching one, exactly the mistake covered in the Processing Duplicate Keys in RPGLE lesson.

Debugging Checklist

If the subfile appears empty for a customer known to have orders, follow the Debugging Subfile Programs lesson's approach: dsply custNbr; right before the SETLL to confirm the key value is correct, then check %EOF immediately after the first READE to confirm whether any record actually matched at all.

Possible Extensions

A natural extension is adding page overflow handling so the column headings reprint on every page for a customer with enough orders to fill more than one screen, using the overflow indicator pattern covered in the Page Overflow Basics lesson, applied here to a subfile control record format instead of a printer file.

Quick Recap

• ORDLSTR combines SETLL/READE with the subfile clear-load-display pattern to list every order for one customer.
• SETLL must come before the READE loop begins.
• Testing should include a customer with several orders, exactly one order, and no orders at all.

Try Asking the AI Tutor

Use the AI Tutor to practice extending or troubleshooting this project. For example, try asking:

• "How would I add a running total of order amounts to ORDCTL, updated as each order loads into the subfile?"
• "What would happen in this program if SETLL were accidentally left out before the READE loop?"