CHGPF there's a quirk that can bite your...

The Change Physical File (CHGPF) is a useful command that allows you to change many attributes of a physical file. Many IBM i (AS400) programmers use it to add fields or change the existing fields without having to recompile file. I do too, as I don't have to do the following:

• Delete all the dependent logical files.
• Make a copy of the phyiscal file with all the data in it.
• Delete the phyiscal file.
• Compile the physical file.
• Copy the data from the copied file into the pysical file.
• Delete the copied file.
• Compile all the dependent logical files.

Generally the rule is in this IT department is that all dependent logical files have the same record format name as the physical. But there are a few odd-ball logical files with a different record format name.

When the physical file was changed using the CHGPF command it caused strange errors in programs that used some of the dependent logical files.

After scratching my head for awhile I worked out what had happened.

In this example I have a physical file, TESTPF, with two dependent logical files, TESTLF and TESTLF2.

The DDS source code for the physical file TESTPF was:

A UNIQUE A R TESTPFR A FLD01 1A TEXT('First field') COLHDG('1st' 'fld') A FLD02 1A TEXT('Second field') COLHDG('2nd' 'fld') A K FLD01

The first logical file, TESTLF, has the same record format name as the phyiscal file:

A R TESTPFR PFILE(TESTPF) A K FLD02

The second, TESTLF2. has a different record format name.

A R TESTLFR PFILE(TESTPF) A FLD01 A FLD02 A K FLD01

By using the Display File Field Description (DSPFFD) command to I confirm that the three files are identical, which they are.

Data Field Buffer Buffer Field Column Field Type Length Length Position Usage Heading FLD01 CHAR 1 1 1 Both 1st fld Field text . . . . . . . . . . . . . . . : First field Coded Character Set Identifier . . . . . : 37 FLD02 CHAR 1 1 2 Both 2nd fld Field text . . . . . . . . . . . . . . . : Second field Coded Character Set Identifier . . . . . : 37

I edit the DDS for TESTPF. I change FLD01 to be 2 alphanumeric, and add a new field called NEW.

A UNIQUE A R TESTPFR A FLD01 2A TEXT('First field') COLHDG('1st' 'fld') A FLD02 1A TEXT('Second field') COLHDG('2nd' 'fld') A NEW 1A TEXT('New field') COLHDG('New' 'fld') A K FLD01

Now I use Change Physical file (CHGPF) command to make the changes. Fill in the fields on the first screen as shown below, and press Enter.

Change Physical File (CHGPF) Type choices, press Enter. Physical file . . . . . . . . . TESTPF Library . . . . . . . . . . . MYLIB System . . . . . . . . . . . . . *LCL Source file . . . . . . . . . . QDDSSRC Library . . . . . . . . . . . MYLIB

And I press Enter a second time when the Additional Parameters are displayed.

After running the CHGPF command I go and check the that files changes were successful using DSPFFD. TESTPF and TESTLF have changed:

Data Field Buffer Buffer Field Column Field Type Length Length Position Usage Heading FLD01 CHAR 2 2 1 Both 1st fld Field text . . . . . . . . . . . . . . . : First field Coded Character Set Identifier . . . . . : 37 FLD02 CHAR 1 1 3 Both 2nd fld Field text . . . . . . . . . . . . . . . : Second field Coded Character Set Identifier . . . . . : 37 NEW CHAR 1 1 4 Both New fld Field text . . . . . . . . . . . . . . . : New field Coded Character Set Identifier . . . . . : 37

Now for the quirk: TESTLF2 is unchanged!

When I move a two character value into FLD01 in either TESTPF or TESTLF, for example ‘12’, only the first character, ‘1’ is displayed in FLD01 in TESTLF2. This could cause big problems for any programs using TESTLF2.

What is causing this? And how can we stop this from happening again?

The cause appears to be that TESTLF2's record format is not the same name as TESTPF's.

One way to fix the problem is to change the record format name in TESTLF2. But TESTLF2 may be designed to only have certain fields in it, and keep the rest unavailable. Once upon a time I built a logical file over the Payroll Employee Master file, it contained only the employee number, name, and department fields. This logical was then used by another application that needed the employees' name and which department they belonged to

I need to identify all of the dependent logical files that do not have the same record format name as the physical file. How do I do this?

First, I would run the Display Data Base Relations (DSPDBR) command. I would just type on a command line:   DSPFD MYLIB/TESTPF   and press Enter. On the screen displayed I type "B" in the Control field and press Enter, to go the bottom of the report. We only care about the ‘Files Dependent on Specified file’ section. In this scenario this is what is displayed:

Files Dependent On Specified File Dependent File Library Dependency JREF Constraint TESTLF MYLIB Data TESTLF2 MYLIB Data

Then I would use the Display File Description (DSPFD) command to get the record format names. I would type on a command line:   DSPFD FILE(MYLIB/TESTLF*) TYPE(*RCDFMT)   and press Enter. By using the wildcard TESTLF* the data for all logical files are included in the same “report”. When the output is displayed use the Find field to scan for the word “Format”:

File . . . . . : QPDSPFD Control . . . . . ________ Find . . . . . . Format *...+....1....+....2....+....3....+....4....+....5....+....6....+ Auxiliary storage pool ID . . . . . . . . . : 00001 Record Format List Record Format Level Format Fields Length Identifier TESTPFR 3 4 324444D952CAD Text . . . . . . . . . . . . . . . . . . . : Total number of formats . . . . . . . . . . : 1 Total number of fields . . . . . . . . . . . : 3 Total record length . . . . . . . . . . . . : 4 File Description Header File . . . . . . . . . . . . . . . . . . . : FILE TESTLF2 Library . . . . . . . . . . . . . . . . . . : MYLIB Type of file . . . . . . . . . . . . . . . : Logical File type . . . . . . . . . . . . . . . . . : FILETYPE *DATA Auxiliary storage pool ID . . . . . . . . . : 00001 Record Format List Record Format Level Format Fields Length Identifier TESTLFR 2 2 336F4C73C9A21

The output shows that TESTLF2's record format name is different from the physical files’s.

I would delete all the logical files with the record format name that are not the same as the physical file’s and then compiled.

To make it easier and quicker for me I have created a program that does the same as the two steps mentioned above that produces a report listing all of a physical file's dependent logicals with their record format names.

You can learn more about the CHGPF command from the IBM website here»

 

This article was written for IBM i 7.1, and it should work with earlier releases too.