|By Joe Rinehart||
|April 13, 2005 12:00 AM EDT||
I saw a one-man band once, and it was quite a sight. He had a bass drum on his back, operated by a cog attached to one ankle, thumping as he stomped his foot. Shoestrings tied to the neck of his guitar would move drumsticks attached to a snare drum perched atop the bass drum.
Another string attached to his right elbow operated a cymbal clamped to the side of the snare drum. I spotted duct tape in more than one place. It was a little complicated, and changing anything was bound to affect everything else.
Does this sound like an application you may have worked on? I'll admit it: it sure sounds familiar to me.
Now, I've also seen some very good orchestras. The conductor runs the show. She doesn't necessarily know how to play the viola or the sousaphone, but she knows how to use her musicians, and trusts them to do their jobs.
I don't know about you, but I'd much rather be a conductor. My musicians could change how their instruments worked, but as long as they still played in tune, it wouldn't matter to me. More importantly, I can add new instruments without having to learn to play them or figuring out how to tie, clamp, tape, and/or tack weld them into place.
That's a powerful paradigm, and this power is what the Model-View-Controller (MVC) design pattern gives you.
What Is Model-View-Controller?According to James Dempsey's "Model-View-Controller Song," MVC is a way of organizing your code into "functional segments so your brain does not explode." MVC divides your application into three layers, each with a clearly defined task:
The Model contains all of the business logic and data in your application. It is not a stretch to say that your Model literally is your application. Typically, a Model consists entirely of objects or services such as CFCs, Java classes, and / or Web Services. A Model never has any knowledge of Views or Controllers.
A View is what the user sees, and is how the user interacts with your application. The View's job is to allow user input and display the "state of the Model," an Object-Oriented (OO) way of saying "your application's data." Most often, Views are traditional ColdFusion pages (.cfm). Other mediums such as Flash can also act as views. Because your Model isn't aware of the Views, you can interchange views without affecting your overall application.
The Controller is simply "glue" code that passes data back and forth between the View and the Model. The Controller takes data from the user, such as form data, and gives it to the Model for processing. The results are then given back to the View, which is shown to the user.
While some users of MVC may object to passing the data back through the Controller, it's a common way to implement the MVC pattern in a Web environment. In a desktop application, however, the View might be allowed to ask the Model for its state information directly. However, because of the nature of the Web, it's a lot easier to simply "push" the state information into the View through the Controller.
Why Use Model-View-Controller?I'm sure we've all heard talk about separating "business logic" from "presentation logic," and MVC does exactly that. By putting the Controller in between the Model (business logic) and View (presentation), we're insuring that they're not only separate, but highly reusable because they're not specific to a particular implementation. Additional Views can use the same Model without any modification. More importantly, the internal working of the Model can change without affecting the Views. This should sound familiar: we've arrived at the power described earlier when I said I'd rather be a conductor than a one-man band. Let's revisit what I said earlier, but change a few words:
"My components could change how their internals worked, but as long as they kept the same interface, it wouldn't matter to me. More importantly, I can add new components without having to learn how they work, just how to use them."
That's a very powerful statement to make about application design. Model-View-Controller utilizes Object-Oriented Design concepts known as "decoupling" and "separation of concerns" to achieve this power. In a "traditional" ColdFusion application, each page is responsible for a good deal: business logic, data access logic, presentation logic, and data validation. By isolating the business logic in the Model and the presentation logic in the View and having the two communicate through the Controller, we've "decoupled" the business layer from the presentation layer. Each of the three layers has a responsibility, or "concern" that is separate from the others. As long as the boundaries along which the layers communicate, or "interfaces," remain the same each layer can change its internal functionality without affecting other the other two.
Let's Code: An MVC ExampleBuilding an MVC application in ColdFusion isn't very hard. You'll just need a good understanding of ColdFusion Components (CFCs) and an open mind. If you're not up and running with ColdFusion Components, you may want to read Jeffry Houser's article entitled "ColdFusion Components" when you're through with this article (CFDJ vol. 6, issue 11).
First, we need a problem to Model. For a fun example, I've chosen to Model translation of English phrases into Pig Latin. For our first attempt, I'm implementing a very simple version of Pig Latin - for any given word, move all consonants until the first vowel to the end of the word, and then add "ay." For example, "Model-View-Controller" becomes "odelMay iewVay ontrollerCay."
It's easy enough to encapsulate all the logic for this into a CFC. Listing 1 shows the entire model for our application, contained in PigLatinizer.cfc. You'll see that it has a single method ("Translate") that receives a string, and returns a translated string. At this point, we have a working "Model" of our "problem domain" - translating phrases into Pig Latin.
Now, we need a View to interact with our model. Listing 2 shows our basic translator form. It has a form field that collects a phrase to translate, a submit button, and will optionally show results of the latest translation.
Well, that was easy. We have a Model and View. Now we need a Controller to glue the two together. One approach many have taken is to simply add pseudo-Controller code to the top of their View pages, closely mimicking the standard self-posting form architecture ColdFusion developers have used for years. However, this places the Controller code in your View, eliminating any chance of re-use. Instead of doing this, we're going to use a CFC called PigLatinController. The source code for PigLatinController.cfc is shown in Listing 3. Examining the code reveals that it's pretty simple. There's an empty constructor ("Init") and a single method ("Translate"). While our constructor here remains empty, in the real world, this may be a place to insert information, such as datasource names or other configuration data, that the controller will need to pass along to the Model.
Examining the Translate method shows a controller in action. It first creates the needed portions of the model - in this case, simply an instance of PigLatinizer.cfc. It then passes data from the View (form.phrase) to the Translate method of the PigLatinizer. The user is then redirected to the view, with the resulting translation passed as a URL variable.
Now we have a Model, a View, and a Controller. What we're still lacking, however, is a way to have them all "talk." This is a where a framework is needed.
Building a Simple FrameworkWhile there are two popular frameworks available for what we need to do (Fusebox and Mach-II), we're going to build our own mini-framework using about ten lines of code. It's going to be bare-bones, but it should get the job done while also introducing the need for more robust, application-agnostic frameworks.
Listing 4 shows our Pig Latin's Application.cfm file, where lines 3 - 13 represent our framework. First, we see if the application is initialized. If it's not, we create an instance of our Controller, placing it into the application scope. Second, we examine the URL scope to see if a parameter named "method" exists. If it does, we CFInvoke that method of our controller.
Running Our ApplicationWe've now built a complete MVC application for translating phrases to Pig Latin. Let's step through two page requests, initial and form post, to trace how the pieces of MVC work together.
Initially, the user requests Index.cfm. ColdFusion processes the Application.cfm file. Our framework insures that an instance of PigLatinController (the Controller) exists in the application scope, and then looks for URL.Method. Because URL.Method doesn't exist, no action is taken. Index.cfm (the View) then presents the user with the appropriate form.
The user then enters a phrase and clicks the submit button, and our next request cycle begins.
Again, ColdFusion processes the Application.cfm file and insures that our Controller exists. This time, however, URL.Method is defined, and its value is "Translate." Our mini-framework recognizes this, and invokes the "Translate" method of the Controller.
Inside the Controller, the "Translate" method creates an instance of PigLatinizer (our Model). It passes the data from the View (form.phrase) into the Model's "Translate" method, and collects the result. The Controller then CFLocates the user back to Index.cfm, appending the result of the translation to the URL. Index.cfm, the View, shows the "state of the model" (the translated phrase), and dutifully re-displays the translation form.
Modifying Our ApplicationBecause we've placed the Controller between the Model and the View, changes to the Model won't affect the View, and vice versa. Realizing our implementation of Pig Latin isn't complete and that there are additional rules for handling words beginning with vowels, we need to modify our Model. Luckily, there's a freely available Java class that translates English into Pig Latin. We can modify our Model to use this class instead of its own internal logic (Listing 5 shows this modification). Because we're only changing its internals, and not altering its interface, the rest of our application will remain unaffected. By isolating our changes, and decoupling our business logic from our presentation logic, we've given ourselves a both more powerful and safer way to alter or scale our application.
The Need for FrameworksOur bare-bones framework is fine for our Pig-Latin translator, but I wouldn't want to develop an enterprise application with it. On a low level, the method of processing input in the controller then CFLocating would make it hard to return meaningful validation results - the URL string could become huge! On a higher level, what if one method of the Controller needed to call another method? It'd be easy to add the code to do so, but this may begin to fall outside of the "concern" of the controller (passing data between the View and the Model) and may begin to fall into the realm of business logic or application design. Frameworks such as Fusebox and Mach-II help out in this problem. By removing this control of "flow" from the Controller and letting you organize your application using XML, they both allow the Controller to assume its proper role of passing data. Frameworks have a number of other advantages, but that's another article.
SummaryModel-View-Controller is an elegant way to divide your application into logical layers. Each layer has a single job, and does it well. The Model represents your application's business logic. The View presents data from the Model, and accepts user input. The Controller serves to pass data between the View and the Model. Most importantly, the Controller serves to decouple the View from the Model, isolating what changes to bring unprecedented power to your application's design.
Further ReadingThis article provided a high-level introduction to Model-view-controller. Hopefully, it's gotten you interested in using MVC to simplify and enhance your application designs. However, it's glossed over a good deal of Object-Oriented concepts and terminology. There's a lot to learn about the theory of MVC and the various design patterns that are used inside of it (MVC is technically a "compound" pattern, made up of other design patterns).
If you're ready to jump into using MVC for ColdFusion applications, I'd begin by taking a look at the Fusebox (www.fusebox.org), Model-Glue (www.model-glue.com) and Mach-II (www.mach-ii.com) frameworks.".
|Derek 05/04/05 10:45:24 AM EDT|
Where is the sample code for this?
"delaPlex is a software development company. We do team-based outsourcing development," explained Mark Rivers, COO and Co-founder of delaPlex Software, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Jul. 29, 2016 01:00 PM EDT Reads: 2,078
ReadyTalk has expanded the capabilities of the FoxDen collaboration platform announced late last year to include FoxDen Connect, an in-room video collaboration experience that launches with a single touch. With FoxDen Connect, users can now not only engage in HD video conferencing between iOS and Android mobile devices or Chrome browsers, but also set up in-person meeting rooms for video interactions. A host’s mobile device automatically recognizes the presence of a meeting room via beacon tech...
Jul. 29, 2016 12:15 PM EDT Reads: 212
On Dice.com, the number of job postings asking for skill in Amazon Web Services increased 76 percent between June 2015 and June 2016. Salesforce.com saw its own skill mentions increase 37 percent, while DevOps and Cloud rose 35 percent and 28 percent, respectively. Even as they expand their presence in the cloud, companies are also looking for tech professionals who can manage projects, crunch data, and figure out how to make systems run more autonomously. Mentions of ‘data science’ as a skill ...
Jul. 29, 2016 11:46 AM EDT Reads: 265
SYS-CON Events announced today that LeaseWeb USA, a cloud Infrastructure-as-a-Service (IaaS) provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. LeaseWeb is one of the world's largest hosting brands. The company helps customers define, develop and deploy IT infrastructure tailored to their exact business needs, by combining various kinds cloud solutions.
Jul. 29, 2016 11:15 AM EDT Reads: 1,337
Amazon has gradually rolled out parts of its IoT offerings in the last year, but these are just the tip of the iceberg. In addition to optimizing their back-end AWS offerings, Amazon is laying the ground work to be a major force in IoT – especially in the connected home and office. Amazon is extending its reach by building on its dominant Cloud IoT platform, its Dash Button strategy, recently announced Replenishment Services, the Echo/Alexa voice recognition control platform, the 6-7 strategic...
Jul. 29, 2016 11:15 AM EDT Reads: 673
The cloud market growth today is largely in public clouds. While there is a lot of spend in IT departments in virtualization, these aren’t yet translating into a true “cloud” experience within the enterprise. What is stopping the growth of the “private cloud” market? In his general session at 18th Cloud Expo, Nara Rajagopalan, CEO of Accelerite, explored the challenges in deploying, managing, and getting adoption for a private cloud within an enterprise. What are the key differences between wh...
Jul. 29, 2016 09:45 AM EDT Reads: 2,130
For basic one-to-one voice or video calling solutions, WebRTC has proven to be a very powerful technology. Although WebRTC’s core functionality is to provide secure, real-time p2p media streaming, leveraging native platform features and server-side components brings up new communication capabilities for web and native mobile applications, allowing for advanced multi-user use cases such as video broadcasting, conferencing, and media recording.
Jul. 29, 2016 09:45 AM EDT Reads: 1,031
SYS-CON Events announced today that Venafi, the Immune System for the Internet™ and the leading provider of Next Generation Trust Protection, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Venafi is the Immune System for the Internet™ that protects the foundation of all cybersecurity – cryptographic keys and digital certificates – so they can’t be misused by bad guys in attacks...
Jul. 29, 2016 09:45 AM EDT Reads: 1,468
There will be new vendors providing applications, middleware, and connected devices to support the thriving IoT ecosystem. This essentially means that electronic device manufacturers will also be in the software business. Many will be new to building embedded software or robust software. This creates an increased importance on software quality, particularly within the Industrial Internet of Things where business-critical applications are becoming dependent on products controlled by software. Qua...
Jul. 29, 2016 07:15 AM EDT Reads: 1,645
In addition to all the benefits, IoT is also bringing new kind of customer experience challenges - cars that unlock themselves, thermostats turning houses into saunas and baby video monitors broadcasting over the internet. This list can only increase because while IoT services should be intuitive and simple to use, the delivery ecosystem is a myriad of potential problems as IoT explodes complexity. So finding a performance issue is like finding the proverbial needle in the haystack.
Jul. 29, 2016 06:45 AM EDT Reads: 2,370
Machine Learning helps make complex systems more efficient. By applying advanced Machine Learning techniques such as Cognitive Fingerprinting, wind project operators can utilize these tools to learn from collected data, detect regular patterns, and optimize their own operations. In his session at 18th Cloud Expo, Stuart Gillen, Director of Business Development at SparkCognition, discussed how research has demonstrated the value of Machine Learning in delivering next generation analytics to imp...
Jul. 29, 2016 04:45 AM EDT Reads: 2,572
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
Jul. 29, 2016 04:15 AM EDT Reads: 2,684
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develo...
Jul. 29, 2016 02:45 AM EDT Reads: 1,617
SYS-CON Events announced today that MangoApps will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides modern company intranets and team collaboration software, allowing workers to stay connected and productive from anywhere in the world and from any device.
Jul. 29, 2016 02:30 AM EDT Reads: 1,470
Large scale deployments present unique planning challenges, system commissioning hurdles between IT and OT and demand careful system hand-off orchestration. In his session at @ThingsExpo, Jeff Smith, Senior Director and a founding member of Incenergy, will discuss some of the key tactics to ensure delivery success based on his experience of the last two years deploying Industrial IoT systems across four continents.
Jul. 29, 2016 02:00 AM EDT Reads: 1,700
Basho Technologies has announced the latest release of Basho Riak TS, version 1.3. Riak TS is an enterprise-grade NoSQL database optimized for Internet of Things (IoT). The open source version enables developers to download the software for free and use it in production as well as make contributions to the code and develop applications around Riak TS. Enhancements to Riak TS make it quick, easy and cost-effective to spin up an instance to test new ideas and build IoT applications. In addition to...
Jul. 29, 2016 12:15 AM EDT Reads: 2,015
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
Jul. 28, 2016 11:45 PM EDT Reads: 1,281
"We've discovered that after shows 80% if leads that people get, 80% of the conversations end up on the show floor, meaning people forget about it, people forget who they talk to, people forget that there are actual business opportunities to be had here so we try to help out and keep the conversations going," explained Jeff Mesnik, Founder and President of ContentMX, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Jul. 28, 2016 10:15 PM EDT Reads: 1,454
"There's a growing demand from users for things to be faster. When you think about all the transactions or interactions users will have with your product and everything that is between those transactions and interactions - what drives us at Catchpoint Systems is the idea to measure that and to analyze it," explained Leo Vasiliou, Director of Web Performance Engineering at Catchpoint Systems, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York Ci...
Jul. 28, 2016 10:00 PM EDT Reads: 2,109
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 19th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo Silicon Valley Call for Papers is now open.
Jul. 28, 2016 09:00 PM EDT Reads: 2,735