Subfile Record Format vs Subfile Control Record Format

Learning Objective

By the end of this lesson, you will be able to clearly explain the difference between a subfile record format and a subfile control record format, and why every subfile actually needs both.

Simple Explanation

This is the single most important distinction to get right before working with subfiles, and it is worth being especially careful about, since it is a common early point of confusion. A working subfile is always built from two separate record formats, not one:

• The subfile record format defines the layout of a single row within the list, the fields that repeat once for every record shown, such as an order number and order date in an order list. This record format is marked as a subfile using the DDS keyword SFL.
• The subfile control record format manages the subfile as a whole: it defines the fixed parts of the screen around the list, such as column headings, a title, and function key instructions, and it contains the keywords, covered in the next lesson, that actually control whether the subfile is displayed and how many rows are shown. This record format is tied to its subfile record format using the DDS keyword SFLCTL, naming the subfile record format it manages.

A helpful way to keep these straight: the subfile record format is the repeating row, one for each record in the list. The subfile control record format is the surrounding frame, appearing once, that holds everything else on the screen and governs how the list behaves. Neither one works on its own; a subfile is always this pair, working together.

Why It Matters

Every subfile keyword and pattern covered in the lessons that follow assumes you already know which of these two record formats it belongs to. Column headings, titles, and function key indicators generally belong on the control record format; the fields that repeat for each record belong on the subfile record format itself. Getting this pairing backwards is one of the most common early mistakes beginners make with subfiles.

Practical Example

Imagine building the order list screen described in the previous lesson. The subfile record format, perhaps named ORDSFL, would define fields for one order's number and date, repeating for each order shown. A separate subfile control record format, perhaps named ORDCTL, tied to ORDSFL using SFLCTL(ORDSFL), would define the screen's title, "Order List," column headings above the list, and a note at the bottom about which function keys are available.

This is a simplified, illustrative example rather than a specific real screen, but it reflects exactly how every subfile is structured: one record format for the repeating rows, one for the surrounding frame.

Common Confusions

"Can I combine the subfile record format and the control record format into one?" No. A subfile always requires both as separate record formats; DDS does not support combining them into a single record format. This separation is a fundamental part of how subfiles work.

"Does the RPGLE program show both record formats separately?" Not exactly separately in the way you might expect. The subfile record format's individual rows are loaded one at a time, but the actual screen display, the subfile alongside its surrounding frame, happens through the control record format, using exfmt on the control record format's name, covered in the next lesson.

"Do the subfile record format and control record format need to look similar in name?" Not strictly, but choosing clearly related names, such as ORDSFL and ORDCTL in the example above, makes it much easier for anyone reading the DDS later to see at a glance which control record format manages which subfile record format.

Quick Recap

• A subfile is always built from two record formats: the subfile record format, marked with SFL, defining one repeating row, and the subfile control record format, marked with SFLCTL, managing the subfile as a whole.
• The subfile record format holds the fields that repeat once per record; the control record format holds the surrounding frame: titles, headings, and function key information.
• SFLCTL names the specific subfile record format a control record format manages, tying the pair together.
• Mixing up which fields or keywords belong on which of these two record formats is one of the most common early subfile mistakes.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "What happens if I put a column heading on the subfile record format instead of the control record format?"
• "Can one subfile control record format manage more than one subfile record format?"