13
Wed, Nov
5 New Articles

RPG Academy: UI Modernization, Part 3—Introducing the MVC

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

Time to introduce a conceptual (but rather useful) new tool for your arsenal: the MVC. No, it’s not a new type of vehicle! It’s the model-view-controller model.

The multi-tier architecture implementations shown in the previous TechTip are a step in the right direction, but they have its limitations:

  • You’re still bound by the DDS limits—Your UIs will still be text-based and limited to a 24x80 or 27x132 green-screen resolution.
  • Your code is not truly separated—Code for screen handling and control flow is still intertwined. It’s true that this approach makes it much easier to maintain, but you still have some code that is not where it should be. This also means that your “UI expert” also has to be the “control flow expert,” when these can be different tasks.

As you can see, this is not a perfect solution. It can work in a lot of situations, but to truly modernize your UI, for instance via a graphical user interface (GUI), you need to completely isolate it from the rest of the code. One proven way to do that is to apply the model-view-controller (MVC) paradigm to your IBM i application. Historically, developers, particularly developers of object-oriented languages, have used the MVC paradigm to implement clear divisions between various components of an application. The term components here refers to the more general definition, not exactly a module, but a group of code pieces of the same type: UI (presentation), processing (business rules enforcement and so on), and data access. The function of most applications is to retrieve data from a database and display it to the user, allowing the user to interact with the data and store updates in the database.

The MVC pattern was developed, as many other great things in IT, by Smalltalk programmers trying to determine the best way to couple event-driven UI objects with the classes that represent the state of the business model. This pattern was adopted by the Java community and incorporated into the Java Swing classes. Many other languages came up with their own implementation of the MVC, such as Microsoft’s ASP.NET MVC, for example.

In today’s fast-paced business world, UIs change much more frequently than the database portions of applications. While this is true for an IBM i-only application, it is even more true in a Web-connected application. Coupling the data and UI of a business application tends to require business logic that goes far beyond the application’s data transmission (or view). Following good design principles pays off when it comes time to make changes to an application’s structure, as you usually do in a modernization initiative. Web services and design paradigms such as the MVC, shown in Figure 1, go a long way in developing and maintaining applications that are feature-rich and capable of handling dynamic content, while supporting a rapid development model to match the business needs.

RPG Academy: UI Modernization, Part 3—Introducing the MVC - Figure 1 

Figure 1: The MVC design pattern (adapted from Sun Microsystem’s original model)

The MVC design pattern splits a program into three layers:

  • The model provides the business logic and data access capabilities of the application and exposes business services.
  • The view displays and collects information from users.
  • The controller intercepts input and translates it into actions performed by the model. In other words, it controls the main flow of the program.

The MVC is somewhat similar to the multi-tier model, but it separates the data access layer from the interface so that the view (i.e., the UI) can be easily replaced or expanded. In the MVC, changes to the model data are reflected in all interfaces, because all views are observers of the data. However, you can change the view (or presentation layer) without any impact to the other two layers. This design pattern also helps ease the maintenance burden by ensuring that changes to the business logic layer are less likely to break the presentation layer, and conversely, that changes to the presentation layer are less likely to break the business logic.

Where the modular approach allowed several RPG programmers to work on different parts (modules) of the same program, the MVC approach facilitates multi-disciplined team development. Developers can focus on creating robust business code without having to worry about breaking the UI, and designers can focus on building useful and engaging UIs without worrying about the language their colleagues are using to develop the business code. As I said before, the “UI experts” don’t need to know RPG at all; they just need to have ways to access the data. The MVC approach facilitates the use of the best tools for each aspect of the development process, such as using RPG for creating the business logic and a combination of HTML, CSS, and JavaScript for creating the UI.

As this is probably new for some readers, it’ll require some additional explanations for the concept of MVC to really sink in and become something useful. Over the next few TechTips, I’ll be talking about each of the layers and how to reengineer an ILE program using the MVC.

Until then, feel free to comment, using the Comments section below.

Rafael Victoria-Pereira

Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.

Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.


MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.

Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Evolve Your RPG Coding: Move from OPM to ILE...and Beyond
Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques.
List Price $79.95

Now On Sale

Flexible Input, Dazzling Output with IBM i Flexible Input, Dazzling Output with IBM i
Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains.
List Price $79.95

Now On Sale

SQL for IBM i: A Database Modernization Guide SQL for IBM i: A Database Modernization Guide
Learn how to use SQL’s capabilities to modernize and enhance your IBM i database.
List Price $79.95

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: