16. Subfiles – ILE RPG in Easy Bytes

You learned how to write inquiry and maintenance programs whose logic required the display of information one record at a time. Some kinds of applications require the use of list panels, in which data from many records is displayed on a screen for review, selection, or update. RPG has a special feature called subfiles to handle this type of program requirement.

Programmers use several different approaches to defining this interrelationship and to loading data into the subfile. The method used depends in part on a program’s anticipated processing requirements: Loading the subfile a page at a time SFLSIZ greater than SFLPAG SFLSIZ equal to SFLPAG Loading the entire subfile When the program loads the subfile a page at a time, each page loads rapidly because the program does not have to read all the records in the file to initially build the list.

Response time is consistent, regardless of the number of records viewed. With this method, the subfile stores only one page of records at a time. Scrolling forward requires replacing the existing page with the next page to be loaded; scrolling backward requires replacing the existing page by reloading the previous page.

Although this method is the easiest to code, it results in the slowest initial response time. Once display begins, however, paging through the subfile is fast because the system handles all paging functions. Using this technique is appropriate when the entire list is relatively small, especially if users may want to see most of the list; it is least appropriate when a large number of records must be loaded and users are unlikely to want to see most of those records.