Welcome!

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

Related Topics: ColdFusion

ColdFusion: Article

Creating and Accessing Collection Files

Creating and Accessing Collection Files

In computer terms, objects are abstracts of real-world entities that are all around us in everyday life. Examples of such objects could be people, organizations, cars, animals, or even less tangible entities such as math or time.

Of these examples, only the first four can be considered collections. One or more persons is a collection of people; one or more organizations is a collection of organizations, and so on. However, math is not a collection of math and time is not a collection of time. They are just simple objects with methods and properties. Simply defined, a collection is a set of related objects.

Several languages already use built-in objects that mimic real-world entities. Many of you may already be familiar with some form of Visual Basic or JavaScript. In Visual Basic, a group of related objects is called a collection. Although the term collection is foreign to the JavaScript language, the language does have objects that act like collections. For instance, the forms object is a collection. You can loop through the collection and access the individual objects using array syntax such as document.forms[0].

Collections come with many advantages. First, they are objects, so any and all advantages of objects, such as encapsulation and reusability, are inherent to the collection. Second, you can access a group of objects easily by looping through the collection and executing the same code against each object in the collection. Finally, you can simplify a lot of the external data manipulation by using collections. For instance, instead of returning a query containing users (which might change in six months) you could use a Users collection. The User object that is stored in the Users collection would encapsulate all the code that goes into retrieving the user data. That way, when the database changes, you can change your User object while your collection and the code accessing the collection remain the same.

What Makes a Collection?
There are three hard and fast rules that an object (or in ColdFusion, a component) has to adhere to in order to be a collection:
1.   Every object in the collection can be accessed individually. Each object in the collection is unique in instance, if not data. If there are five objects in the collection, you should be able to call properties and methods from each object.
2.   Every object in the collection is the same type of object and has the same properties and methods. This means that you wouldn't have a collection called People with two types of objects: People and Computers. You would, in fact, have two collections, the People collection and the Computers collection.
3.   A collection usually has at least four methods: Add, Remove, Count, and Item.

Most collections can be completely accessed through the use of just four methods:

  • Add(): Adds a new object to the collection
  • Remove(): Removes an object from the collection
  • Item(): Retrieves an object from the collection (for use in the application)
  • Count(): Returns the number of objects in the collection (for looping purposes)

    Creating the Collection Files
    In order to create a collection we need to create two files, both of which are CFCs. The first CFC we'll create will be named ActiveUsers.cfc; the second will be named ActiveUser.cfc. The ActiveUser.cfc file will be the actual object that is contained in our collection. The collection filename is usually the plural term for the name of our object, hence, ActiveUser object and ActiveUsers collection. The ActiveUser.cfc file is shown in Listing 1.

    The ActiveUsers collection will have four methods: Add(strFirstName, strLastName), Remove(index), Item(index), and Count(). Our ActiveUser object will contain five methods: GetName(), SetName(strFirstName, strLastName), SetLoginTime(), GetLoginTime(), and GetMinutesActive().

    Our ActiveUsers collection will be used to display only users who are currently active on our Web site, similar to a "who's on" interface. Anytime you access a variable in a shared scope, such as the Application scope, you should lock it using CFLOCK.

    The first step is to set up a data structure to store our data in the ActiveUsers collection. We need only one private (or member) variable called arItems, which is an array. You can add that code just inside of your CFCOMPONENT tag as shown below.

    <CFCOMPONENT>
    <CFSET arItems = ArrayNew(1)>
    </CFCOMPONENT>

    Next we're going to add four methods to the component. The first method is the Add method. The Add method will take two arguments, FirstName and LastName, both string literals. The Add function simply adds an element to the private variable arItems using the intrinsic function, ArrayAppend(). The tricky part is that our Add method needs to add a value that represents an instance of an object. Since we can't use the CFOBJECT tag inside the ArrayAppend() function, we will use the CreateObject() function, shown below. After we add that element to the array, we also need to get the length of the array so we know the index of our recently added user. Again, locking is important here, because we want to add an element to the array and then get the length of the array before anyone else adds another element to it. This is sometimes called a race or race to commit, in database terminology. If we don't lock the actions, we will be racing against other requests to add elements to the array, potentially returning the wrong values to the calling page.

    <CFSET ArrayAppend(arItems, CreateObject("component","ActiveUser")>
    <CFSET idx = ArrayLen(arItems)>

    The next two lines of code in our function will be calling methods from the prebuilt ActiveUser object. These methods set three internal variables in the ActiveUser object: the user's first name, the user's last name, and the date the user logged in.

    <CFSET arItems[idx].SetName(Arguments.FirstName,Arguments.LastName)>
    <CFSET arItems[idx].SetLoginTime(Now())>
    <CFRETURN arItem[idx]>

    The last thing we do is return the current element of the array for the programmer to use in the calling page, if necessary. That was the hard part. The next three functions are short and sweet, so I'm going to spend more time describing why you need to do this, rather than stepping through the code line by line. Listing 2 shows the code for the entire collection object.

    With the Remove method, we require one argument that is an integer representing the index of the internal array, arItems. We need to check to make sure the value passed is less than or equal to the length of the array so there aren't any errors produced, and then we simply remove that element using the ArrayDeleteAt() function. Remember, you'll need to lock this action to prevent the wrong index of the array from being deleted. In a situation where the method is called twice, there will be a race to commit the deletion. In the event the deletion was not locked, the array would be resized after the first deletion and then the wrong index could potentially be deleted during the second deletion.

    The Item method also requires an index value, but the result is different. Instead of removing an item (or doing any type of action), we're just going to return the instance of the ActiveUser object that was stored at that index. This allows us to access each individual object from external ColdFusion templates easily, as you'll see later.

    The Count method accepts no arguments and returns an integer describing the number of objects in our collection. We use the ArrayLen() function to determine the return value.

    That's it for our collection. All of the internal code is written for our ActiveUsers collection to work properly. It's relatively easy to generate code for collections once you understand the concepts. Now we're going to look at how to use collections in ColdFusion templates.

    Making the Collection Persist
    In order for our "who's on" application to persist, we need to set up the ActiveUsers collection in the Application scope. Open the Application.cfm file in Listing 3 and add the following code:

    <CFIF NOT IsDefined("Application.objActiveUsers")>
    <CFOBJECT NAME="Application.objActiveUsers" COMPONENT="ActiveUsers">
    </CFIF>

    This code basically says to check whether the Application.objActiveUsers collection is defined at the beginning of every request. If it isn't defined, it will create the collection using the CFOBJECT tag.

    Accessing the Collection
    In the index.cfm file (see Listing 4) we're going to output the current number of users online and then loop through the ActiveUsers collection and output data pertaining to the users that are online. You can do all this using the code below:

    <CFSET iCount = Application.objActiveUsers.Count()>

    As you'll see, we've set the iCount variable to the value of the ActiveUsers collection's Count method. This lets us know how many active users are online right now. Now we can loop through the collection using a simple FROM/TO (or FOR) loop where the TO attribute is equal to the number of users online, or iCount.

    We can access the individual objects in the collection using the Item(index) property such as Application.objActiveUsers.Item(i). In the code below, we use that notation to call different methods of the object, such as GetName(), GetLoginTime(), and GetMinutesActive().

    <CFLOOP FROM="1" TO="#iCount#" INDEX="i">
    <CFSET stName = Application.objActive
    Users.Item(i).GetName()>
    #i# - #stName["FirstName"]#
    #stName["LastName"]# -
    #DateFormat(Application.objActiveUsers.Item(i).GetLoginTime(), 'm/d/yy')#
    #TimeFormat(Application.objActiveUsers.Item(i).GetLoginTime(), 'h:mm tt')# -
    #Application.objActiveUsers.Item(i).GetMinutesActive()#<BR>
    </CFLOOP>

    Running index.cfm at this point in time would result in the printing of "Number of Users: 0", since we haven't added any users to the collection. In order to add users to the collection we have to call the Add() method of the ActiveUsers collection. In this example, we'll make a ColdFusion page called AddUser.cfm (see Listing 5) that requires two URL variables called FirstName and LastName. The following code is all we'll use for our AddUser.cfm file:

    <CFSET objActiveUser = Application.objActive
    Users.Add(Trim(URL.FirstName),Trim(URL.LastName))>
    <CFLOCATION URL="index.cfm">

    If we access the AddUser.cfm page passing "Steve" and "Parks" through the query string such as

    AddUser.cfm?FirstName=Steve&LastName=Parks

    our page will then add the user to the collection and refresh us to the index.cfm page. You should now see that there is one user named Steve Parks in the collection. If your browser caches the index.cfm page, you may have to manually refresh the page. In the index.cfm file we called the GetName(), GetLoginTime(), and GetMinutesActive() methods from the ActiveUser object in the collection. You'll now see that data outputted through the collection. Try it again, adding another user using your name. You should now see that you are in the collection as well.

    The last file that needs to be created is the RemoveUser.cfm file, which will remove users from the collection. Instead of passing the FirstName or LastName of the user, you'll need to pass a valid index. In this example, we'll just remove the first index, but in theory you would remove users based on an algorithm possibly determined by a method called GetMinutesIdle(). To remove the first user from the application, call the file RemoveUser.cfm, shown in Listing 6, passing a value of 1 in the attribute index, as shown below:

    RemoveUser.cfm?Index=1

    We've now created our ActiveUsers collection in a simplified form. You can add properties and methods to the ActiveUser object to make the system more robust. I recommend adding locking and validation to the Application scope and methods, respectively.

  • More Stories By Steve Parks

    Steve Parks, CEO of Adept Developer Consulting, Inc (www.adeptdeveloper.com), is a Macromedia Certified Advanced Cold Fusion Developer. Steve has seven years experience developing web applications and relational databases.

    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.


    @ThingsExpo Stories
    SYS-CON Events announced today that SOA Software, an API management leader, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. SOA Software is a leading provider of API Management and SOA Governance products that equip business to deliver APIs and SOA together to drive their company to meet its business strategy quickly and effectively. SOA Software’s technology helps businesses to accelerate their digital channels with APIs, drive partner adoption, monetize their assets, and achieve a...
    SYS-CON Events announced today that Aria Systems, the recurring revenue expert, has been named "Bronze Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue business and deliver exceptional experiences to their customers.
    SYS-CON Events announced today that AgilePoint, the leading provider of Microsoft-centric Business Process Management software, will exhibit at SYS-CON's 2nd International @ThingsExpo which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. AgilePoint is the leading provider of Microsoft-based Business Process Management (BPM) software products, has 1,300+ on-premise and cloud deployments in 25+ countries and provides the same advanced BPM feature set as J2EE vendors like IBM and Appian for the Microsoft .NET native environment. AgilePoint customer...
    The Internet of Things (IoT) promises to evolve the way the world does business; however, understanding how to apply it to your company can be a mystery. Most people struggle with understanding the potential business uses or tend to get caught up in the technology, resulting in solutions that fail to meet even minimum business goals. In his session at Internet of @ThingsExpo, Jesse Shiah, CEO / President / Co-Founder of AgilePoint Inc., will show what is needed to leverage the IoT to transform your business. He will discuss opportunities and challenges ahead for the IoT from a market and tec...
    SYS-CON Events announced today that Utimaco will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Utimaco is a leading manufacturer of hardware based security solutions that provide the root of trust to keep cryptographic keys safe, secure critical digital infrastructures and protect high value data assets. Only Utimaco delivers a general-purpose hardware security module (HSM) as a customizable platform to easily integrate into existing software solutions, embed business logic and build s...
    One of the biggest challenges when developing connected devices is identifying user value and delivering it through successful user experiences. In his session at Internet of @ThingsExpo, Mike Kuniavsky, Principal Scientist, Innovation Services at PARC, will describe an IoT-specific approach to user experience design that combines approaches from interaction design, industrial design and service design to create experiences that go beyond simple connected gadgets to create lasting, multi-device experiences grounded in people’s real needs and desires.
    Samsung VP Jacopo Lenzi, who headed the company's recent SmartThings acquisition under the auspices of Samsung's Open Innovaction Center (OIC), answered a few questions we had about the deal. This interview was in conjunction with our interview with SmartThings CEO Alex Hawkinson. IoT Journal: SmartThings was developed in an open, standards-agnostic platform, and will now be part of Samsung's Open Innovation Center. Can you elaborate on your commitment to keep the platform open? Jacopo Lenzi: Samsung recognizes that true, accelerated innovation cannot be driven from one source, but requires a...
    The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at Internet of @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, will discuss how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money! Speaker Bio: Esmeralda Swartz, CMO of MetraTech, has spent 16 years as a marketing, product management, and busin...
    SYS-CON Events announced today that TeleStax, the main sponsor of Mobicents, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. TeleStax provides Open Source Communications software and services that facilitate the shift from legacy SS7 based IN networks to IP based LTE and IMS networks hosted on private (on-premise), hybrid or public clouds. TeleStax products include Restcomm, JSLEE, SMSC Gateway, USSD Gateway, SS7 Resource Adaptors, SIP Servlets, Rich Multimedia Services, Presence Services/RCS, Diame...
    Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, will address the big issues involving these technologies and, more important, the results they will achieve. How important are public, private, and hybrid cloud to the enterprise? How does one define Big Data? And how is the IoT tying all this together?
    We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
    The only place to be June 9-11 is Cloud Expo & @ThingsExpo 2015 East at the Javits Center in New York City. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT & Big Data companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic strategies that utility/cloud computing provides. Whether public, private, or in a hybrid form, clo...
    SYS-CON Events announces a new pavilion on the Cloud Expo floor where WebRTC converges with the Internet of Things. Pavilion will showcase WebRTC and the Internet of Things. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices--computers, smartphones, tablets, and sensors – connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades.
    SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridsto...
    SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...
    As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at Internet of @ThingsExpo, Andrew Bolwell, Director of Innovation for HP’s Printing and Personal Systems Group, will discuss how key attributes of mobile technology – touch input, senso...
    The Internet of Things (IoT) is making everything it touches smarter – smart devices, smart cars and smart cities. And lucky us, we’re just beginning to reap the benefits as we work toward a networked society. However, this technology-driven innovation is impacting more than just individuals. The IoT has an environmental impact as well, which brings us to the theme of this month’s #IoTuesday Twitter chat. The ability to remove inefficiencies through connected objects is driving change throughout every sector, including waste management. BigBelly Solar, located just outside of Boston, is trans...
    Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, will examine three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics...
    Internet of @ThingsExpo Silicon Valley announced on Thursday its first 12 all-star speakers and sessions for its upcoming event, which will take place November 4-6, 2014, at the Santa Clara Convention Center in California. @ThingsExpo, the first and largest IoT event in the world, debuted at the Javits Center in New York City in June 10-12, 2014 with over 6,000 delegates attending the conference. Among the first 12 announced world class speakers, IBM will present two highly popular IoT sessions, which will take place November 4-6, 2014 at the Santa Clara Convention Center in Santa Clara, Calif...
    From a software development perspective IoT is about programming "things," about connecting them with each other or integrating them with existing applications. In his session at @ThingsExpo, Yakov Fain, co-founder of Farata Systems and SuranceBay, will show you how small IoT-enabled devices from multiple manufacturers can be integrated into the workflow of an enterprise application. This is a practical demo of building a framework and components in HTML/Java/Mobile technologies to serve as a platform that can integrate new devices as they become available on the market.