Sidebar

Practical RPG: APIs, Part 2 - Changing Objects Using the QLICOBJD API

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

APIs are one of the most powerful tools provided by the IBM i; here is a practical example of using one.

In my previous article, I explained the basics of error reporting when calling APIs. This next installment brings those basics into focus with a real-world illustration that you can experiment with on your own and also use as a practical addition to your development environment.

Object Descriptions and User-Defined Attributes

We start this project by reviewing the concept of the object description. Remember that, in the IBM i operating system, everything is an object. Programs are objects. Files are objects. Commands, data areas, and job descriptions are all objects. And everything that is an object has a number of common attributes that, taken collectively, form the object description. The operating system provides a command to view those attributes, the humble DSPOBJD command. Figure 1 shows the output.

Practical RPG: APIs, Part 2 - Changing Objects Using the QLICOBJD API - Figure 1

Figure 1: The DSPOBJD command shows basic information about an object.

DSPOBJD shows a lot of object information. The highlighted piece is the user-defined attribute, a 10-character field that is generally blank. This field can be used for anything you need, which can be very useful indeed when you're trying to manage a large system. You can put things like a PTF number in there, or a revision (although for revision I prefer to use a different object field, the eight-character object control level, or OCL). As of version 7.1, you can also use a new 16-character build identifier field.

Today, we're going to take a look at a program that can change the user-defined attribute. In so doing, we're going to review how the various API reporting options work in a real-world situation. If you'd like to use the PTF number or build number, this same program can be easily modified to update any of them.

The Program, CHGUDA

The program we're looking at is CHGUDA, which calls the API QLICOBJD. The complete definition of the API can be found on IBM's website here. The program is very simple, although I've made it a bit more complex than it needs to be in order to showcase the various error-handling techniques. You'll be able to select the error-handling mode via the first parameter. The program calls QLICOBJD, so let's take a look at the prototype for that program.

dcl-pr QLICOBJD extpgm;            

  oLib   char(10);                

  iObjLib char(20) const;      

  iType   char(10) const;      

  iData   like(dsParm) const;      

  iErr   char(1) options(*varsize);

end-pr;                            

                        

dcl-s wLib char(10);              

                                  

dcl-ds dsParm;                    

  num int(10) inz(1);              

  key int(10) inz(9);              

  len int(10) inz(10);            

  data char(10);                  

end-ds;                            

The prototype is relatively simple. The only unusual piece is the first parameter, which is an output field. If you specify a special value for the library name (such as *LIBL), then this parameter will show you the library where the object was found. It's a nice feature. After that, the parameters are pretty straightforward. In the IBM i, objects are identified by two components: the qualified object name and the object type. As is usual in the IBM i APIs, the qualified object name (the iObjLib parameter) is a 20-character field in which the first 10 characters are the object name and the second 10 are the library. The object type is next. After that is the iData field, a variable-length record that is defined in the dsParm data structure. Finally, we have the error data structure.

An important point here is that both iData and iErr can have variable formats. Variable-length records like iData are very common in IBM i APIs. They typically start with a 4-byte integer that specifies the number of entries, followed by one or more variable-length entries. For this particular API, each record has a key number (identifying the field to update), a data length, and then the data itself. Those three valueskey, len, and datacan be repeated as many times as necessary to update multiple fields.

If you require multiple entries in the variable-length record, you need a more sophisticated approach to defining the data than is shown in this program. We're going to go into that in much more detail in a subsequent article on retrieving journal entries. But since we're updating only one field here, we can simplify the process into the single data structure shown in dsParm. The value num is initialized to 1 because there is only one record. Then the three following values come from the API definition: key is initialized to 9, which specifies the user-defined attribute; len is initialized to 10 because the attribute can accept up to 10 characters; and the data field is an uninitialized 10-character field. The data field is the only uninitialized field because it will contain the value that the user wants to be stored in the user-defined attribute.

dcl-ds ApiThrow;                      

  *n int(10) inz(0);                  

  *n int(10) inz(0);                  

end-ds;                                

                                      

dcl-ds ApiIgnore qualified;            

  BytPrv int(10) inz(%size(ApiIgnore));

  BytAvl int(10) inz(0);              

end-ds;                                

                                      

dcl-ds ApiError qualified;            

  BytPrv   int(10) inz(%size(ApiError));

  BytAvl   int(10) inz(0);            

  MsgID   char(7);                    

  reserved char(1);                    

  MsgDta   char(80);                  

end-ds;                                

This section of the program should be familiar if you read the previous article. I've created the three basic error-handling structures. ApiThrow is the most basic and is typically used only when an error is a fatal error. Errors cause a hard halt in the program, just like any other unhandled exception. ApiIgnore is also quite simple and is used when any errors are going to be ignored. You can check for an error; if one occurs, the BytAvl field will be set to a non-zero value. But that's the only information you get. If you need to condition your logic based on the specific error encountered, then you need to use the ApiError structure. Now let's see how this all fits together in the program.

dcl-pi *n;                                                    

  iMode char(1);                                              

  iLib char(10);                                              

  iObj char(10);                                              

  iType char(10);                                            

  iAttr char(10);                                            

end-pi;                                                      

                                                              

dcl-s wLib char(10);                                          

dcl-s wMsg char(50);                                          

                                                              

data = iAttr;                                                

                                                              

select;                                                      

  when iMode = 'T';                                          

    QLICOBJD( wLib: iObj+iLib: iType: dsParm: ApiThrow);      

  when iMode = 'I';                                          

    QLICOBJD( wLib: iObj+iLib: iType: dsParm: ApiIgnore);    

    if ApiIgnore.BytAvl <> 0;                                

      wMsg = %char(ApiIgnore.BytAvl) + ' bytes of error data.';

    endif;                                                    

  when iMode = 'E';                                          

    QLICOBJD( wLib: iObj+iLib: iType: dsParm: ApiError);      

    wMsg = ApiError.MsgID + ' ' + ApiError.MsgDta;            

endsl;                                                        

                                                              

if wMsg <> '';                                                

  dsply wMsg;                                                

endif;                                                        

                                                              

*inlr = *on;                                                  

return;                                                      

As you can see, the program is not complicated. The first portion is the procedure interface (if you're unfamiliar with the concept, the procedure interface in the main section of the program performs the same function as the *ENTRY PLIST in an older RPG program). This program has five parameters: the mode (which we'll cover in a moment), the library of the object, the object name, the object type, and finally the value we want placed in the user-defined attribute. You could call it from the command line like this:

CALL CHGUDA PARM(T MYLIB MYPGM *PGM MYATTR02)

After the procedure interface, a couple of work fields are defined. Then the work starts.

Remember that we noted that the data field in the dsParm structure was the only field not pre-initialized. That's because it was intended to send whatever value the user specified to the QLICOBJD API. The next line does just that. And then we begin a big select statement base on the mode. The idea here is that you can experiment with the API error-handling by changing the mode that you send to the program. If you specify T as the first parameter, then any errors cause a hard halt. The halt itself is not particularly informative (it just says that an error occurred calling QLICOBJD), but the joblog will tell you what actually happened.

CALL PGM(CHGUDA) PARM(T MYLIB MYPGM *PGM ATTR002)                  

Library MYLIB not found.

Function check. CPF9810 unmonitored by CHGUDA at statement 0000000052

  instruction X'0000'.

The call to *LIBL/QLICOBJD ended in error (C G D F).              

Mode I (selected by specifying I, for Ignore, for the first parameter) uses the ApiIgnore structure, which will ignore the error, but the program will display that an error occurred.

DSPLY 26 bytes of error data.

In this case, you would be checking for an error. For example, you might try to create a data area and assume that any error means it already exists. Then you try to change the data area and use the ApiThrow, so any errors cause a halt.

Finally, you can use mode E (for Error), which shows the error information. While this program simply displays the message ID and message data, you could actually retrieve the formatted message or write the information to disk to a log file for later retrieval. Here's what the result of that call looks like:

DSPLY CPF9810 MYLIB

You may notice that this is the same message ID we saw in the joblog using the T (Throw) mode.

So now that we've gone through all the possible error-handling cases, let's see what happens when we call the program with good parameters.

 

CALL PGM(CHGUDA) PARM(T PBDUTIL CHGUDA *PGM ATTR002)                  

No errors are thrown, so the program ran successfully. If I run the DSPOBJD command again, I see this as the user-defined data:

User-defined information:                                                  

Attribute . . . . . . . . . . . . . : ATTR002                                  

Text . . . . . . . . . . . . . . . . : Change User Defined Attribute

And that's exactly the result we wanted. So to conclude, this article shows you how to call an API and use the various API error techniques to condition your code. We used the powerful variable-length record format, but we used a very simplified version of it. Next we're going to see how to build up complex parameters using a similar technique.

Have fun with your APIs!

 

 

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 joepluta@plutabrothers.com.


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

More Articles By This Author
Related Articles
BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

RESOURCE CENTER

  • WHITE PAPERS

  • WEBCAST

  • TRIAL SOFTWARE

  • White Paper: Node.js for Enterprise IBM i Modernization

    SB Profound WP 5539

    If your business is thinking about modernizing your legacy IBM i (also known as AS/400 or iSeries) applications, you will want to read this white paper first!

    Download this paper and learn how Node.js can ensure that you:
    - Modernize on-time and budget - no more lengthy, costly, disruptive app rewrites!
    - Retain your IBM i systems of record
    - Find and hire new development talent
    - Integrate new Node.js applications with your existing RPG, Java, .Net, and PHP apps
    - Extend your IBM i capabilties to include Watson API, Cloud, and Internet of Things


    Read Node.js for Enterprise IBM i Modernization Now!

     

  • Profound Logic Solution Guide

    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 companyare not aligned with the current IT environment.

    Get your copy of this important guide today!

     

  • 2022 IBM i Marketplace Survey Results

    Fortra2022 marks the eighth edition of the IBM i Marketplace Survey Results. Each year, Fortra captures data on how businesses use the IBM i platform and the IT and cybersecurity initiatives it supports.

    Over the years, this survey has become a true industry benchmark, revealing to readers the trends that are shaping and driving the market and providing insight into what the future may bring for this technology.

  • Brunswick bowls a perfect 300 with LANSA!

    FortraBrunswick is the leader in bowling products, services, and industry expertise for the development and renovation of new and existing bowling centers and mixed-use recreation facilities across the entertainment industry. However, the lifeblood of Brunswick’s capital equipment business was running on a 15-year-old software application written in Visual Basic 6 (VB6) with a SQL Server back-end. The application was at the end of its life and needed to be replaced.
    With the help of Visual LANSA, they found an easy-to-use, long-term platform that enabled their team to collaborate, innovate, and integrate with existing systems and databases within a single platform.
    Read the case study to learn how they achieved success and increased the speed of development by 30% with Visual LANSA.

     

  • Progressive Web Apps: Create a Universal Experience Across All Devices

    LANSAProgressive Web Apps allow you to reach anyone, anywhere, and on any device with a single unified codebase. This means that your applications—regardless of browser, device, or platform—instantly become more reliable and consistent. They are the present and future of application development, and more and more businesses are catching on.
    Download this whitepaper and learn:

    • How PWAs support fast application development and streamline DevOps
    • How to give your business a competitive edge using PWAs
    • What makes progressive web apps so versatile, both online and offline

     

     

  • The Power of Coding in a Low-Code Solution

    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:

    • Discover the benefits of Low-code's quick application creation
    • Understand the differences in model-based and language-based Low-Code platforms
    • Explore the strengths of LANSA's Low-Code Solution to Low-Code’s biggest drawbacks

     

     

  • Why Migrate When You Can Modernize?

    LANSABusiness 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.
    In this white paper, you’ll learn how to think of these issues as opportunities rather than problems. We’ll explore motivations to migrate or modernize, their risks and considerations you should be aware of before embarking on a (migration or modernization) project.
    Lastly, we’ll discuss how modernizing IBM i applications with optimized business workflows, integration with other technologies and new mobile and web user interfaces will enable IT – and the business – to experience time-added value and much more.

     

  • UPDATED: Developer Kit: Making a Business Case for Modernization and Beyond

    Profound Logic Software, Inc.Having trouble getting management approval for modernization projects? The problem may be you're not speaking enough "business" to them.

    This Developer Kit provides you study-backed data and a ready-to-use business case template to help get your very next development project approved!

  • What to Do When Your AS/400 Talent Retires

    FortraIT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators is small.

    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:

    • Why IBM i skills depletion is a top concern
    • How leading organizations are coping
    • Where automation will make the biggest impact

     

  • Node.js on IBM i Webinar Series Pt. 2: Setting Up Your Development Tools

    Profound Logic Software, Inc.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. In Part 2, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Attend this webinar to learn:

    • Different tools to develop Node.js applications on IBM i
    • Debugging Node.js
    • The basics of Git and tools to help those new to it
    • Using NodeRun.com as a pre-built development environment

     

     

  • Expert Tips for IBM i Security: Beyond the Basics

    SB PowerTech WC GenericIn this session, IBM i security expert Robin Tatam provides a quick recap of IBM i security basics and guides you through some advanced cybersecurity techniques that can help you take data protection to the next level. Robin will cover:

    • Reducing the risk posed by special authorities
    • Establishing object-level security
    • Overseeing user actions and data access

    Don't miss this chance to take your knowledge of IBM i security beyond the basics.

     

     

  • 5 IBM i Security Quick Wins

    SB PowerTech WC GenericIn today’s threat landscape, upper management is laser-focused on cybersecurity. You need to make progress in securing your systems—and make it fast.
    There’s no shortage of actions you could take, but what tactics will actually deliver the results you need? And how can you find a security strategy that fits your budget and time constraints?
    Join top IBM i security expert Robin Tatam as he outlines the five fastest and most impactful changes you can make to strengthen IBM i security this year.
    Your system didn’t become unsecure overnight and you won’t be able to turn it around overnight either. But quick wins are possible with IBM i security, and Robin Tatam will show you how to achieve them.

  • Security Bulletin: Malware Infection Discovered on IBM i Server!

    SB PowerTech WC GenericMalicious programs can bring entire businesses to their knees—and IBM i shops are not immune. It’s critical to grasp the true impact malware can have on IBM i and the network that connects to it. Attend this webinar to gain a thorough understanding of the relationships between:

    • Viruses, native objects, and the integrated file system (IFS)
    • Power Systems and Windows-based viruses and malware
    • PC-based anti-virus scanning versus native IBM i scanning

    There are a number of ways you can minimize your exposure to viruses. IBM i security expert Sandi Moore explains the facts, including how to ensure you're fully protected and compliant with regulations such as PCI.

     

     

  • Encryption on IBM i Simplified

    SB PowerTech WC GenericDB2 Field Procedures (FieldProcs) were introduced in IBM i 7.1 and have greatly simplified encryption, often without requiring any application changes. Now you can quickly encrypt sensitive data on the IBM i including PII, PCI, PHI data in your physical files and tables.
    Watch this webinar to learn how you can quickly implement encryption on the IBM i. During the webinar, security expert Robin Tatam will show you how to:

    • Use Field Procedures to automate encryption and decryption
    • Restrict and mask field level access by user or group
    • Meet compliance requirements with effective key management and audit trails

     

  • Lessons Learned from IBM i Cyber Attacks

    SB PowerTech WC GenericDespite the many options IBM has provided to protect your systems and data, many organizations still struggle to apply appropriate security controls.
    In this webinar, you'll get insight into how the criminals accessed these systems, the fallout from these attacks, and how the incidents could have been avoided by following security best practices.

    • Learn which security gaps cyber criminals love most
    • Find out how other IBM i organizations have fallen victim
    • Get the details on policies and processes you can implement to protect your organization, even when staff works from home

    You will learn the steps you can take to avoid the mistakes made in these examples, as well as other inadequate and misconfigured settings that put businesses at risk.

     

     

  • The Power of Coding in a Low-Code Solution

    SB PowerTech WC GenericWhen 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:

    • Discover the benefits of Low-code's quick application creation
    • Understand the differences in model-based and language-based Low-Code platforms
    • Explore the strengths of LANSA's Low-Code Solution to Low-Code’s biggest drawbacks

     

     

  • Node Webinar Series Pt. 1: The World of Node.js on IBM i

    SB Profound WC GenericHave 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.
    Part 1 will teach you what Node.js is, why it's a great option for IBM i shops, and how to take advantage of the ecosystem surrounding Node.
    In addition to background information, our Director of Product Development Scott Klement will demonstrate applications that take advantage of the Node Package Manager (npm).
    Watch Now.

  • The Biggest Mistakes in IBM i Security

    SB Profound WC Generic The Biggest Mistakes in IBM i Security
    Here’s the harsh reality: cybersecurity pros have to get their jobs right every single day, while an attacker only has to succeed once to do incredible damage.
    Whether that’s thousands of exposed records, millions of dollars in fines and legal fees, or diminished share value, it’s easy to judge organizations that fall victim. IBM i enjoys an enviable reputation for security, but no system is impervious to mistakes.
    Join this webinar to learn about the biggest errors made when securing a Power Systems server.
    This knowledge is critical for ensuring integrity of your application data and preventing you from becoming the next Equifax. It’s also essential for complying with all formal regulations, including SOX, PCI, GDPR, and HIPAA
    Watch Now.

  • Comply in 5! Well, actually UNDER 5 minutes!!

    SB CYBRA PPL 5382

    TRY 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.

    Request your trial now!

  • Backup and Recovery on IBM i: Your Strategy for the Unexpected

    FortraRobot automates the routine 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:
    - Simplified backup procedures
    - Easy data encryption
    - Save media management
    - Guided restoration
    - Seamless product integration
    Make sure your data survives when catastrophe hits. Try the Robot Backup and Recovery Solution FREE for 30 days.

  • Manage IBM i Messages by Exception with Robot

    SB HelpSystems SC 5413Managing messages on your IBM i can be more than a full-time job if you have to do it manually. 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:
    - Automated message management
    - Tailored notifications and automatic escalation
    - System-wide control of your IBM i partitions
    - Two-way system notifications from your mobile device
    - Seamless product integration
    Try the Robot Message Management Solution FREE for 30 days.

  • Easiest Way to Save Money? Stop Printing IBM i Reports

    FortraRobot 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:

    - Automated report distribution
    - View online without delay
    - Browser interface to make notes
    - Custom retention capabilities
    - Seamless product integration
    Rerun another report? Never again. Try the Robot Report Management Solution FREE for 30 days.

  • Hassle-Free IBM i Operations around the Clock

    SB HelpSystems SC 5413For over 30 years, Robot has been a leader in systems management for IBM i.
    Manage your job schedule with the Robot Job Scheduling Solution. Key features include:
    - Automated batch, interactive, and cross-platform scheduling
    - Event-driven dependency processing
    - Centralized monitoring and reporting
    - Audit log and ready-to-use reports
    - Seamless product integration
    Scale your software, not your staff. Try the Robot Job Scheduling Solution FREE for 30 days.