HOT TIPS: DDS (7 Tips)

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RTNDTA Keyword Trick

The DDS keyword Return Data (RTNDTA) can eliminate the need to create separate variable names in display files used for database file updates. The display file can reference the database fields instead. No need to worry about field attributes matching between the database file and the display file. I don't have to code any MOVEs or Z-ADDs, and my program size is smaller since there are not as many variables. Here's how it's done.

DDS coding:

Place the RTNDTA keyword at the record level on the appropriate record of the display file. Use the database field names and reference the database file. This will bring the database fields into the display file automatically when you retrieve the database record.

RPG coding:

1. CHAIN and release the database record (place an N in position 53).

2. Display the screen.

3. Perform a READ or EXFMT operation on the screen and determine if the user has made any changes. If so, CHAIN again to the database record.

4. Reread the display format using the READ operation. This is what makes this technique work. (Normally, if I CHAINed again to the database record, the internal representation of the display file record would be overlaid and any changes to the display record would be lost.) By reading the display record again with the RTNDTA keyword, you retrieve the values from the screen.

5. Update the database record.

The DDS manual is a good reference where this keyword is concerned.

Color My World Windows

We write all of our maintenance programs as DDS windows. While in an application, the user has the ability to call up one or more maintenance program windows. The DDS WINDOW keyword allows you to dynamically control the position of the window on your screen, but doesn't allow the color to be controlled. A way around this is to use the WDWBORDER keyword in your display file. We allow up to seven different colors to be chosen by coding seven WDWBORDER keywords, each conditioned by a different indicator.

To give each window displayed a different border color, the first time the program is called, pass it a one-byte decimal field initialized to zero. The window program receives this window color parameter, adds one to it, then sets the indicator for that particular color. On subsequent program calls, pass it the same parameter, making sure you don't change it. Each time the program is called, it adds one to get a different color. If the color exceeds seven (the limit), the program resets it to one. This gives each successive window a different color.

Creating a View over a Packed MDY Date

If you are stuck with a packed MMDDYY date field and need to create a logical access path by date over the file, you can break it down using the substring feature in DDS. To do this you must first override its definition to zoned, because technically you cannot substring a packed numeric field. The Substring (SST) keyword uses three parameters: the field name, the starting position and the result length. The result must be defined as input only and is always character. (Note that since you are specifying at least one field, you must list all of the other fields from the physical file.)

Physical File Definition:

 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 . A R RECORD A FLD1 3 0 COLHDG('FIELD #1') A FLD2 1 COLHDG('FIELD #2') A MMDDYY 6 0 COLHDG('DATE') A K FLD1 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 . 

Logical by YYMMDD Date:

 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 A R RECORD PFILE(FILENAME) A FLD1 A FLD2 A MMDDYY S A FLDYY I SST(MMDDYY 5 2) A FLDMM I SST(MMDDYY 1 2) A FLDDD I SST(MMDDYY 3 2) A K FLDYY A K FLDMM A K FLDDD ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 

An Easy Way to Handle the SFLEND Indicator

If you've ever used the SFLEND keyword in your subfiles, you know that this keword requires an indicator. There is an easy way to handle this requirement. Assign your response indicator (F3, F12, etc.) to your SFLEND statement and use its negative condition as illustrated below.

 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 A CA03(03) * A N03 SFLEND(*MORE) 

With this method, you don't have to search for an unused indicator and your RPG program doesn't have to set the indicator on. The F3 response indicator will never be on while the record is displayed; therefore, the SFLEND keyword will always be active.

DDS Keyword for System Name and User Profile

The DDS keyword SYSNAME automatically incorporates the system name into your display files. It works much like the two other DDS keywords, DATE and TIME, which have been in existence for years.

By the same token, there's a DDS keyword, USER, which brings the user profile name to your display files. Both SYSNAME and USER can be easily added to your display files while in SDA by using the *SYSNAME and *USER commands; again, this works like *DATE and *TIME.

It's too bad IBM didn't take this a bit further and make SYSNAME and USER available to printer files as well as display files. After all, DATE and TIME can be included in printer files.

Resetting DDS PAGNBR

For those of you who use externally described printer files and want an easy way to reset your file's page number (PAGNBR), you may not be aware of a technique that allows you to do it quite easily. There are three parts to the technique:

1. Use two statements instead of one to define the PAGNBR field: one for the end position and one for the PAGNBR keyword.

2. Condition the PAGNBR keyword with an indicator.

3. When you want to reset the page number to 1, set on the PAGNBR conditioning indicator. When the indicator is off, the page number increments by one each time it is written. The page number always prints, whether the indicator is off or on. After resetting the page number, be sure to set the indicator off to continue with automatic page numbering. The following code illustrates this technique.

Page Numbering DDS:

 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 . A R HDR SKIPB(5) A 115'PAGE....:' A 129 A 02 PAGNBR A EDTCDE(Z) A SPACEA(1) ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 . 

RPG Code to Reset DDS PAGNBR:

 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 . C MOVEL*ON *IN02 C WRITEHDR C MOVEL*OFF *IN02 

Add Meaning to Display File Indicator

A good way to make your programs more readable and easier to maintain is to use the simple technique of renaming display file response indicators. Response indicators are those that are assigned to keywords (e.g., ROLLUP, ROLLDOWN, CFxx, CAxx). By using an RPG "I" specification with the applicable display file record format name, you can rename any *IN response indicator to a descriptive name such as ROLLUP, EXIT or PROMPT. Not only will your programs be more readable, but by looking at your "I" specifications, you can instantly cross-reference all of your command keys. Unfortunately, option indicators (the indicators that condition display file fields) cannot be renamed.

 ... 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+ IDSPFL01 I *IN03 EXIT I *IN04 PROMPT I *IN61 ROLLUP 
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