Sidebar

How MVC Can Simplify and Modernize Your IBM i Applications

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

Want to make your big ol’ RPG programs more modular and easier to maintain? Then give the MVC design pattern a try.

Editor’s note: This article is excerpted from chapter 24 of 21st Century RPG: /Free, ILE, and MVC.

Model-View-Controller (MVC) is a design pattern. Unlike many of the design patterns that have been defined, it is not uniquely oriented to object-oriented (OO) programming, but can easily be used with procedural languages as well.

Nor is it related to some sort of programming or communication issue. Instead, it is uniquely suited to the types of applications we run in the business world: applications where we access data, display it somewhere, make changes to it, take it back in, edit it in various ways, and write it back out to the spot it originally came from.

Now before I go any further, I want to make one thing clear. When I use the term “MVC” I am using it in a generic, not specific sense. That is, in a specific sense, MVC is a very specific design pattern that has very specific requirements and attributes.

It is actually part of a family that is loosely called “MVC.” This family consists of MVC plus MVP (Model-View-Presenter), MVA (Model-View-Adapter), MVVM (Model-View-ViewModel), HMVC (Hierarchical Model-View-Controller), and others. Each of these has very specific properties; the particular format I will be using is probably more MVP than MVC.

For more information about MVC specifics, I suggest Martin Fowler’s excellent article “GUI Architectures” on his website).

What Is MVC?

At a practical level, MVC is a pattern consisting of a number of separate modules of the following types:

  • The Model is somewhat misnamed in my opinion, but it’s too late to do anything about that now. Essentially the model is the business rules, the logic, that you want to apply in your application. It may or may not contain the access code to get to the data.
  • View is pretty self-explanatory; it is the code required to display the information that we have accessed or the user wants to enter.
  • Controller is the code that ties the other two together, acting as the traffic cop that tells the logic flow when to go to the appropriate module.

Generally, you will have multiple model and view modules. That is, it’s quite probable that you will have a number of screens in this function, and each one would be a separate view module. Similarly, you could easily have several models, each one oriented around retrieving or processing a specific type of data. Usually, however, there is only one controller module, although that is a guideline, not a rule. (Although now that I am editing this, I can’t imagine you needing two controller segments. Maybe it should be a rule.)

What is a rule is that whatever you code up, it should fit into one, and only one, of these categories (model, view, or controller). And it should be true to the spirit of ILE: each module should have basically one and only one logical idea behind it.

After that, it is a bit of a judgment call.

For example, some people feel very strongly that you need to separate out your data access logic from the model code. And in some ways that makes sense, particularly if there is much chance that you will change the database or platform that you are on. If you separate the data access, it makes the app much more portable. For us on the IBM i, that is probably not going to happen (unless you switch from DDS to DB2), and so for simplicity I believe in keeping the data access code in with the logic statements in the model. But that’s just me. And most normal people.

Other people get fixated on the relationship between the model and the view.

In theory, the controller should be the intermediary between the model and the view, but the fact that MVC is always shown as a triangle lets some people build connections between the logic and the display.

There is a version of MVC called MVP—Model-View-Presenter—that is specifically designed to not allow communication between the model and the view. Everything has to go through the controller. I sort of prefer this.

There is also MVA—Model-View-Adapter, which to me seems identical to MVP, although I would never suggest that to a partisan of either.

There is also the MVVM—Model-View-ViewModel, which allows the unthinkable to happen, for the model and the view to communicate with each other via slightly different types of view modules.

I hate to be blunt about this, but I really find it very hard to care. I guess I am more in favor of not allowing the logic (model) and the display (view) to talk to each other, but if it happens I am not going to consider my life a failure. I’ve got a lot of other reasons besides that. No, we are going to look at a middle-of-the-road implementation of MVC and get on with our lives.

Why MVC Is Important

OK, MVC breaks things into specific pieces. Big hairy deal. Like the whole world is about to explode, and they changed the cast for the third Fantastic Four movie, and Peter Jackson just won’t stop making crummy movies that rewrite the two greatest books ever written, and you think I care about MVC? Hey, pal, I got real things to worry about.

But the truth is, we should care at least a little about MVC. And I’ll tell you why.

I do not believe in the wholesale rewriting of applications to make them “modern.” Or at least, I don’t believe in rewriting the whole thing in terms of some other language, such as Java. And yet, RPG is incapable of producing those cute little GUI screens that are so in today. What’s a body to do?

What I am in favor of is taking the big ol’ programs (BOPs) that are out there for an application and breaking them down into model, controller, and view modules. Then I would redo the model and controller RPG code using /Free and ILE. And I would then be free to redo the view portion in whatever Web language is the most exciting at the time.

And so, for me, MVC is a requirement for any modernization.

But it goes beyond modernization. MVC is a requirement to get your programs set so that they are maintainable into the future.

I mean, forget modernization. You don’t need to do that to have your RPG programs continue to function just as they are today. And you can add additional functionality to them to make them even more valuable. But doing that to many BOPs is easier said than done, and when you are done, the program will undoubtedly look even worse than it did before. Going to MVC simplifies and cleans up these programs.

Quite simply, MVC is the next iteration in i program structure. It is replacing the more or less single program app structure with the MVC format. That should be the basis of any modernization that you do.

Everybody Loves MVC, but ...

At this point, you may be tempted to go out to the Web, google MVC, and see what you get. I guarantee it will be a ton. MVC is very widely used, extremely well known, and very effective. And yet, most of the articles that you see will probably be some variation of “MVC is great, but this is what’s wrong with it.”

The reason for that is that most of the articles on MVC are written by Web language people. And things on the Web are more complicated than things in the i world. There are a lot of issues and situations that are standard for them, which just don’t come up for us. As a result, there are a lot more things that can “go wrong” with the relatively simple MVC design pattern. Things like inversion of control and dependency injection. Some of the implementations of MVC, like MVVM, tend to be slow and difficult to implement (don’t even get Dave Bush started). And, since MVC is a design pattern, it does not really force you to do anything. So you can use MVC and still write very complex and disjointed programs. Or have a high degree of data coupling. Or intermix functionality, so that view logic is somehow embedded in the model or model logic shows up in the controller.

OK, so MVC isn’t perfect. If you are determined to screw it up, you will. Common sense and basic programming disciplines are still necessary.

But, MVC does provide a framework to allow you to write applications with a couple of very important characteristics.

First, MVC does force you to be modular, and in an RPG world that is still heavily involved with BOPs, that is an important fact.

Second, it makes a pretty strong effort to separate business logic from the view process from the program flow (control) actions. Yes, you can mess that up, but if you are paying even just a little attention, that shouldn’t happen.

Third, it provides the only way to have flexibility to change your view method and maybe even your database, without having to go through a major rewrite.

And those are the things that I want us to focus on as we develop an example of a /Free-based, ILE-using MVC design pattern application: specifically, modularity and separation of function, two of the keys to developing truly modern applications.

What Ya Shoulda Learned

  • You should know how to spell MVC.
  • And you should know what it stands for: Model (business logic), View (the display of the data), Controller (application flow control).
  • The real thing you need to know is how to create an MVC application rather than doing a BOP. And that is what we will look at next.
David Shirey

David Shirey is president of Shirey Consulting Services, providing technical and business consulting services for the IBM i world. Among the services provided are IBM i technical support, including application design and programming services, ERP installation and support, and EDI setup and maintenance. With experience in a wide range of industries (food and beverage to electronics to hard manufacturing to drugs--the legal kind--to medical devices to fulfillment houses) and a wide range of business sizes served (from very large, like Fresh Express, to much smaller, like Labconco), SCS has the knowledge and experience to assist with your technical or business issues. You may contact Dave by email at dave@shireyllc.com or by phone at (616) 304-2466.


MC Press books written by David Shirey available now on the MC Press Bookstore.

21st Century RPG: /Free, ILE, and MVC 21st Century RPG: /Free, ILE, and MVC
Boost your productivity, modernize your applications, and upgrade your skills with these powerful coding methods.
List Price $69.95

Now On Sale

More Articles By This Author
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.