02
Sat, Nov
2 New Articles

Practical RPG: Handling Flat Files with Multiple Record Formats

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

Sometimes an old technique with a new tweak is the best answer. This article shows you how to externally describe multi-format flat files from partners or legacy systems.

 

It's often the little things that can make a big difference in the world of RPG, and often an older technique can come to the rescue when dealing with the thorny issues of the real world. A perfect example is dealing with flat files having multiple formats. While externally described files can't handle them, a mix of old and new techniques can give you the next best thing.

The Setup

Let's take a simple situation. I've got a trading partner or a third-party package that is sending me order information. These orders come in a flat file, 256 bytes per record, with three different layouts: Order Header, Order Address, and Order Detail. The Order Header record has basic order information, such as customer information and order-level values. An order will have at least one Order Address record containing street address and contact information. The order might have multiple records--for example, one each for ship-to and bill-to addresses. Finally, the Order Detail record contains item number, quantity, and price information.

 

In order to minimize complexity, the order data is passed in a single file with different formats for each record type. One standard technique is to give all records an ID, usually in the first few bytes of the record. This ID specifies the format of the rest of the record. The data is also sequenced so that the highest-level record (in this case, the order header) is first, followed by all the details records. This allows the processing program to use the header information when processing the detail.

 

How the processing occurs is very dependent on the business requirements; it ranges from immediately trying to post the data to writing a transaction file, which is later posted in batch processing. This article isn't worried about the posting process; instead, it will focus more on reading the flat file data.

First Things First

The first thing to do is to create an externally described data structure for each format. For example, the order header information might be stored in a file called ORDHDR, like so:

 

R ORDHDRR                                         

  RECID          2A         TEXT('Record Type')   

  CUSTNUM        6S 0       TEXT('Customer Number')

  CUSTNAME      30A         TEXT('Customer Name') 

  CUSTNAME      25A         TEXT('Customer PO')   

  ORDERED        8S 0       TEXT('Ordered Date')  

  DELIVERY       8S 0       TEXT('Delivery Date') 

  TAX            9S 2       TEXT('Total Tax')     

  SHIPPER        4A         TEXT('Shipper Code')  

  FREIGHT        7S 2       TEXT('Freight')       

 

Here's the order address record:

 

R ORDADRR                                       

  RECID          2A         TEXT('Record Type') 

  ADDRTYPE       2A         TEXT('Address Type')

  ADDR1         30A         TEXT('Line 1')      

  ADDR2         30A         TEXT('Line 2')      

  ADDR3         30A         TEXT('Line 3')      

  CONTACT       30A         TEXT('Contact Name')

  PHONE         15A         TEXT('Contact Phone')

  EMAIL         80A         TEXT('Contact Email')

 

And finally the order detail:

 

R ORDDTLR                                         

  RECID          2A         TEXT('Record Type')   

  ITEMNUMBER    15A         TEXT('Item Number')   

  QUANTITY       7S 0       TEXT('Quantity')      

  UNITPRICE      9S 4       TEXT('Unit Price')    

  EXTAMOUNT     11S 2       TEXT('Extended Amount')

  WEIGHT         7S 2       TEXT('Weight')        

  TAXCODE        4A         TEXT('Tax Code')      

  SHIPCODE       4A         TEXT('Ship Code')     

 

In this particular example, you might notice that most of the information is calculated by the order system: for example, the price, tax, and freight information is all sent in the flat file. In this case, the posting process simply needs to verify the information and post in. In another environment, the posting process might be required to compute prices and dates. That wouldn't affect the use of this technique; it would simply mean that less information is sent in the flat file.

Implementing the Technique

Now for the program. As I normally do, I'll walk you through each piece of the program and explain what it does.

 

A    H OPTION(*NODEBUGIO:*SRCSTMT)

 

These are standard compile options that make debugging easier.

 

B    FORDERS    IF   F  256        DISK

 

OK, here we define the file. The file name is ORDERS and records are 256 bytes long. The file is internally described and not sequenced. Usually, this would involve creating input specifications, but through the magic of data structures we get to avoid that tedious and error-prone step.

 

C    d dsOrdHdr      e ds           256    extname('ORDHDR') qualified

 

This line defines the header as a data structure named dsOrdHdr. This is an externally described data structure with two important characteristics. First is that this particular record is not defined as BASED, meaning that RPG actually allocates space for this record. The other records, dsOrdAdr and dsOrdDtl, are defined as BASED, and I'll return to that momentarily. Second is that I've defined the length as 256. This ensures that the entire record is read.

 

D    d dsOrdAdr      e ds           256    extname('ORDADR') qualified

D    d                                     based(pOrder)

D    d dsOrdDtl      e ds           256    extname('ORDDTL') qualified

D    d                                     based(pOrder)

D    d pOrder          s               *   inz(%addr(dsOrdHdr))

 

These two records are defined just like the order header, except that they are defined as BASED with a pointer named pOrder. That pointer, pOrder, is specified to be initialized to the address of dsOrdHdr. The result of this is that all three data structures actually occupy the same 256 bytes. Thus, when you read into dsOrdHdr, you read into all three data structures.

 

      /free

E      read ORDERS dsOrdHdr;

E      dow not %eof(ORDERS);

 

The rest of the code is simple. This is a standard loop: read the record and end when you hit end of file.

 

F        select;

F          when dsOrdHdr.RECID = 'OH';

F            // ProcessHeader();

F          when dsOrdHdr.RECID = 'OA';

F            // ProcessAddress();

F          when dsOrdHdr.RECID = 'OD';

F            // ProcessDetail();

F        endsl;

 

Here, you use the RECID field to determine which procedure to call to process the record.

 

E        read ORDERS dsOrdHdr;

E      enddo;

 

This is the bottom of the read loop.

 

G      *inlr = *on;

      /end-free

 

This technique has pros and cons, and the use of BASED data structures may be overkill for your application. An alternative would be to have separate data structures for each record type. The program would read into a dummy data structure that defines only the record ID and then move the record into the appropriate data structure, based on the contents of the record ID field. Using separate data structures is simpler (not requiring BASED data structures), but it also requires more data movement. On the other hand, when the data structures share memory, as in this example, you have to remember to save everything you need from the current record because the next read will wipe out the previous record. It's up to you; I'm simply showing you the technique. It's always good to have as many options as possible.

Joe Pluta

Joe Pluta is the founder and chief architect of Pluta Brothers Design, Inc. He has been extending the IBM midrange since the days of the IBM System/3. Joe uses WebSphere extensively, especially as the base for PSC/400, the only product that can move your legacy systems to the Web using simple green-screen commands. He has written several books, including Developing Web 2.0 Applications with EGL for IBM i, E-Deployment: The Fastest Path to the Web, Eclipse: Step by Step, and WDSC: Step by Step. Joe performs onsite mentoring and speaks at user groups around the country. You can reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..


MC Press books written by Joe Pluta available now on the MC Press Bookstore.

Developing Web 2.0 Applications with EGL for IBM i Developing Web 2.0 Applications with EGL for IBM i
Joe Pluta introduces you to EGL Rich UI and IBM’s Rational Developer for the IBM i platform.
List Price $39.95

Now On Sale

WDSC: Step by Step WDSC: Step by Step
Discover incredibly powerful WDSC with this easy-to-understand yet thorough introduction.
List Price $74.95

Now On Sale

Eclipse: Step by Step Eclipse: Step by Step
Quickly get up to speed and productivity using Eclipse.
List Price $59.00

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: