MODULE 9 · INDEXED FILES AND SORT · 5/8

REWRITE and DELETE

14 min30 XPExercise

A master file is not write-once. Customers move, balances change, accounts close. Open the file I-O and you get three verbs besides READ:

Verb	Does	Fails with
`WRITE`	Adds a new record	`22` key already exists
`REWRITE`	Replaces the record with the same key	`23` no such key (random/dynamic)
`DELETE file RECORD`	Removes the record with that key	`23` no such key

Read, change, rewrite

To change one field you must first READ the record (so the rest of it is in the record area), change the field, then REWRITE:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. PARTMNT.
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT PART-FILE ASSIGN TO PARTMAST
               ORGANIZATION IS INDEXED
               ACCESS MODE IS DYNAMIC
               RECORD KEY IS PART-NO
               FILE STATUS IS WS-FS.
       DATA DIVISION.
       FILE SECTION.
       FD PART-FILE.
       01 PART-REC.
          05 PART-NO      PIC X(4).
          05 PART-QTY     PIC 9(4).
       WORKING-STORAGE SECTION.
       01 WS-FS           PIC XX.
       PROCEDURE DIVISION.
           OPEN OUTPUT PART-FILE
           MOVE "A1000050" TO PART-REC
           WRITE PART-REC
           MOVE "B2000007" TO PART-REC
           WRITE PART-REC
           CLOSE PART-FILE

           OPEN I-O PART-FILE
           MOVE "A100" TO PART-NO
           READ PART-FILE
               NOT INVALID KEY
                   ADD 25 TO PART-QTY
                   REWRITE PART-REC
                   DISPLAY "A100 NOW " PART-QTY
           END-READ
           MOVE "B200" TO PART-NO
           DELETE PART-FILE RECORD
               NOT INVALID KEY DISPLAY "B200 DELETED"
           END-DELETE
           MOVE "B200" TO PART-NO
           DELETE PART-FILE RECORD
               INVALID KEY DISPLAY "B200 AGAIN: STATUS " WS-FS
           END-DELETE
           CLOSE PART-FILE
           STOP RUN.

Output:

A100 NOW 0075
B200 DELETED
B200 AGAIN: STATUS 23

Notice that DELETE takes the file name (DELETE PART-FILE RECORD) while WRITE and REWRITE take the record name. It is an old inconsistency and a favourite interview question.

Rules that bite

You cannot change the primary key with REWRITE. The key identifies which record to replace. To "rename" a key, WRITE a new record and DELETE the old one.
In ACCESS SEQUENTIAL, REWRITE and DELETE apply to the record you just read, so a successful READ must come first. If the key field changed in between you get status 21.
In RANDOM or DYNAMIC, DELETE needs only the key. No READ first.
Check the status every time. INVALID KEY covers 22/23; anything else, like a 9x hardware or logic error, needs a FILE STATUS check.

Transaction-driven maintenance

Real maintenance programs read a file of transactions, each carrying an action code, and apply them one by one:

           EVALUATE TR-CODE
               WHEN "A" PERFORM ADD-ACCOUNT
               WHEN "U" PERFORM UPDATE-ACCOUNT
               WHEN "D" PERFORM DELETE-ACCOUNT
           END-EVALUATE

Each paragraph moves the transaction key into the record key, issues one verb, and reports success or a rejection. The rejects go to an error report that someone in operations works through the next morning.

On the job

While your batch job has a KSDS open I-O, the online (CICS) region usually can't update it: VSAM share options, and whether CICS has the file open, decide who gets to write. That is why master-file updates run in the overnight batch window, and why a batch job that overruns into the morning is a phone call you don't want.

Your task

Apply the day's account maintenance to the account master in place.

DD TRANIN — line sequential, 36-byte transactions:

Field	PIC	Notes
`TR-CODE`	`X`	`A` add, `U` update, `D` delete
`TR-ID`	`X(6)`	account number
`TR-NAME`	`X(20)`	used by `A` only
`TR-AMOUNT`	`9(7)V99`	`A`: opening balance, `U`: amount to add

DD ACCTMAST — indexed, key ACCT-ID: ACCT-ID X(6), ACCT-NAME X(20), ACCT-BAL 9(7)V99. Open it I-O.

For each transaction, in file order:

A → write a new record: ADDED nnnnnn
U → read it, add TR-AMOUNT to the balance, rewrite: UPDATED nnnnnn
D → delete it: DELETED nnnnnn
any failure → REJECTED c nnnnnn STATUS ss with the real file status

Then display MASTER AFTER UPDATE: and list the whole master in key order: ACCT-ID, space, ACCT-NAME, space, balance edited Z,ZZZ,ZZ9.99. The starter already has the reject paragraph and the listing.

← Browsing with START and READ NEXT SORT with USING and GIVING →

Run your program to see its output here. The first visible test's input and datasets are used.

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