Mini Project: Subfile Row Selection with Detail Screen

What We Are Building

An extended version of the Simple Order List Subfile mini project's ORDLSTR, adding an option field so a user can select one order from the list and drill into a separate detail screen showing that order's full information.

Business Scenario

The Simple Order List Subfile mini project let a representative see every order for a customer, but only as a flat list of order numbers and amounts. This project adds the natural next step: selecting one specific order from that list to actually look at it more closely.

Concepts Used

• Option fields and a READC loop, from the Option Fields in Subfile Screens and Selecting a Row in a Subfile lessons.
• CHAIN and %FOUND, reused from the Customer Inquiry Program mini project.
• Calling a second display file from RPGLE, extending the single-screen pattern used throughout this batch.

Files and Programs Involved

• ORDHIST, already used by ORDLSTR.
• ORDSFLD, extended from the Simple Order List Subfile mini project with an added option field on its ORDSFL subfile record format.
• ORDDTLD, a new, small display file with one record format, ORDDFMT, showing one order's full detail.
• ORDLSTR, extended to read the selected option and call the detail screen.

Step-by-Step Build Outline

1. Add an option field to ORDSFLD's ORDSFL subfile record format, exactly as covered in the Option Fields in Subfile Screens lesson.
2. Design ORDDTLD's ORDDFMT record format showing order number, amount, and an F12 "return" key.
3. Load the subfile exactly as in the Simple Order List Subfile mini project, then exfmt ORDCTL.
4. After exfmt, loop through the subfile with READC, checking each row's option field for a selection, covered in the Selecting a Row in a Subfile lesson.
5. On a selected row, exfmt ORDDFMT to show that order's detail, then return to the subfile screen.

Example Code

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

exfmt ORDCTL;

readc ORDSFL;
dow not %eof(ORDSFLD);
  if OPTION = 1;
    chain ORDNBR ORDHIST;
    if %found(ORDHIST);
      exfmt ORDDFMT;
    endif;
  endif;

  readc ORDSFL;
enddo;

Here, readc ORDSFL; reads only the rows a user actually changed on screen, exactly as covered in the Selecting a Row in a Subfile lesson. OPTION = 1 checks whether that row was flagged for selection; if so, chain ORDNBR ORDHIST; retrieves that exact order's full record, and exfmt ORDDFMT shows it on the separate detail screen.

How to Test It

Load the subfile with several orders, select one with option 1, and confirm the detail screen shows the correct order's information. Select a different order on a later pass and confirm the detail screen updates to match. Test with no selection at all, confirming the loop completes without unnecessarily calling the detail screen.

Common Mistakes

• Using READ instead of READC, which would process every subfile row rather than only the ones the user actually changed.
• Forgetting to CHAIN and check %FOUND before calling exfmt ORDDFMT, risking showing stale or blank detail fields for a row that somehow no longer matches.
• Forgetting to reset the option field after handling a selection, which could cause the same row to be treated as selected again later.

Debugging Checklist

If selecting a row does not open the detail screen, follow the Debugging Subfile Programs lesson's approach: add a temporary dsply showing OPTION's value inside the READC loop to confirm the selection is actually being read as expected.

Possible Extensions

A natural extension is adding a second option, such as 2 for editing the order directly from the detail screen, following the same option- field pattern already covered in the Option Fields in Subfile Screens lesson.

Quick Recap

• This project adds row selection and a detail screen to the Simple Order List Subfile mini project's flat list.
• READC reads only changed subfile rows; checking the option field identifies which one was selected.
• Testing should cover selecting different rows and selecting none 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 second option letting the user delete an order directly from this subfile?"
• "What would happen if the option field were never reset after being handled?"