You will be redirected in 30 seconds or close now.

ColdFusion Authors: Yakov Fain, Jeremy Geelan, Maureen O'Gara, Nancy Y. Nee, Tad Anderson

Related Topics: ColdFusion, Adobe Flex

ColdFusion: Article

Don't Talk to Strangers!

ColdFusion components and the Law of Demeter

"Don't talk to strangers" may sound like the advice your mother used to give you as a child, but as is so often the case, mother knows best. As we'll soon see, "don't talk to strangers" or "only talk to your friends" is advice that can apply to programming as well. In programming terms, this general concept is known as the Law of Demeter, and it's a great programming practice that facilitates a reduction in coupling between objects in object-oriented applications.

Before you turn to the next article and dismiss this as applicable to OO programming but having no relevance to your procedural Fusebox application, read on as you'll see that the benefits of the Law of Demeter can easily be gained in any application that uses ColdFusion components (CFCs). By applying the Law of Demeter, you can reduce coupling between your CFCs and make your application more flexible and easy to maintain.

First let's investigate the concept of coupling. Coupling is the degree to which one object is dependent upon another or, in the case of ColdFusion, the degree to which one CFC is dependent upon another CFC. For example, if CFC A is used by CFCs B and C and the CFCs are tightly coupled, a change to CFC A will also likely impact CFCs B and C. Minimizing coupling between CFCs is an important goal as you develop your applications.

Have you ever worked on an application in which you have changed something that appears to be quite a small, isolated part of the system, but changes to this seemingly isolated part result in the application grinding to a halt? Perhaps that's an extreme example, but you don't want to make a change to a ColdFusion component in an application and have it all come crashing down because of the huge amount of dependencies between that component and other components within the application.

Systems that have low coupling reduce the impact of changes, thus making them easier to maintain. We all like things to be easier to maintain, right?

With all this talk of coupling, you may be getting the impression that any coupling whatsoever is a bad thing to have in your application. A key point to remember, however, is that a small amount of coupling is necessary in order for your application to do anything. It is unnecessary coupling that we should strive to avoid. In addition, coupling to stable, well-designed components such as the components in the ColdFusion MX 7 Admin API is generally safe as these are unlikely to change significantly in a way that will break backward compatibility.

As you build CFCs and attempt to avoid unnecessary coupling, it's helpful to think of each CFC as exposing an API to other components in the system. By exposing a public API, each CFC can hide its inner workings from other components so that outside components need only know how to communicate with the CFC, but they don't need to know any of the details related to how the CFC performs its functions.

In ColdFusion, components can be coupled in one of the following ways:

  • If CFC X calls a function on CFC Y, component X is said to be coupled to component Y.
  • If CFC X contains a variable (either in a variables scope or locally inside a function) that is a reference to CFC Y, component X is said to be coupled to component Y.
  • If CFC X extends CFC Y, component X is said to be coupled to component Y.
  • If CFC X receives an instance of CFC Y as an argument to one of its functions or an instance of CFC Y is returned from a function called on another CFC, then...
Well, you're probably starting to get the picture. Recognizing coupling and avoiding unnecessary coupling is an important skill that you'll want to develop as you build your applications.

The Law of Demeter
The Law of Demeter was first defined by Ian Holland while working on The Demeter project at Northeastern University in 1987. In brief, the Law of Demeter states that an object should only call methods that:

  • Belong to itself (i.e., its own methods)
  • Are on objects passed in as a parameter
  • Are on objects created by the object
A full summary of the Law of Demeter can be found at www.cmcrossroads.com/bradapp/docs/demeter-intro.html. Translating this to ColdFusion, this means your component should only call its own functions, functions of components it contains, or functions of components passed in to its own functions. An easier way to remember this is basically a CFC should not call functions on components that are returned from other CFCs. For example, the following violates the Law of Demeter:

<cfset myPostalCode = person.getAddress().getPostCode() />

In the following example, we have a Person CFC that contains an address CFC held internally in the variables scope with a function named getPostCode, and getPostCode returns a postal code. To retrieve the person's postal code we may write something along the lines of this:

<cfset me = createObject("component","person") />
<cfset postcode = me.getAddress().getPostCode() />

Or maybe the following, which is really just a variation of the code above:

<cfset me = createObject("component","person") />
<cfset myHouse = me.getAddress() />
<cfset postcode = myHouse.getPostCode() />

More Stories By Kola Oyedeji

Kola Oyedeji is technical director of Vivid Lime, a London-based full services agency. Prior to that, he was a senior software developer for the Collinson Group, developing Enterprise Loyalty and Insurance Systems. Kola holds a BSc in Computer and Information systems. His blog is available at www.coolskool.blog-city.com.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

IoT & Smart Cities Stories
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...
DXWorldEXPO LLC announced today that Big Data Federation to Exhibit at the 22nd International CloudEXPO, colocated with DevOpsSUMMIT and DXWorldEXPO, November 12-13, 2018 in New York City. Big Data Federation, Inc. develops and applies artificial intelligence to predict financial and economic events that matter. The company uncovers patterns and precise drivers of performance and outcomes with the aid of machine-learning algorithms, big data, and fundamental analysis. Their products are deployed...
All in Mobile is a place where we continually maximize their impact by fostering understanding, empathy, insights, creativity and joy. They believe that a truly useful and desirable mobile app doesn't need the brightest idea or the most advanced technology. A great product begins with understanding people. It's easy to think that customers will love your app, but can you justify it? They make sure your final app is something that users truly want and need. The only way to do this is by ...
The challenges of aggregating data from consumer-oriented devices, such as wearable technologies and smart thermostats, are fairly well-understood. However, there are a new set of challenges for IoT devices that generate megabytes or gigabytes of data per second. Certainly, the infrastructure will have to change, as those volumes of data will likely overwhelm the available bandwidth for aggregating the data into a central repository. Ochandarena discusses a whole new way to think about your next...
CloudEXPO | DevOpsSUMMIT | DXWorldEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
Cell networks have the advantage of long-range communications, reaching an estimated 90% of the world. But cell networks such as 2G, 3G and LTE consume lots of power and were designed for connecting people. They are not optimized for low- or battery-powered devices or for IoT applications with infrequently transmitted data. Cell IoT modules that support narrow-band IoT and 4G cell networks will enable cell connectivity, device management, and app enablement for low-power wide-area network IoT. B...
The hierarchical architecture that distributes "compute" within the network specially at the edge can enable new services by harnessing emerging technologies. But Edge-Compute comes at increased cost that needs to be managed and potentially augmented by creative architecture solutions as there will always a catching-up with the capacity demands. Processing power in smartphones has enhanced YoY and there is increasingly spare compute capacity that can be potentially pooled. Uber has successfully ...
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things'). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing. IoT is not about the devices, its about the data consumed and generated. The devices are tools, mechanisms, conduits. This paper discusses the considerations when dealing with the...