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
    The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
    Cultural, regulatory, environmental, political and economic (CREPE) conditions over the past decade are creating cross-industry solution spaces that require processes and technologies from both the Internet of Things (IoT), and Data Management and Analytics (DMA). These solution spaces are evolving into Sensor Analytics Ecosystems (SAE) that represent significant new opportunities for organizations of all types. Public Utilities throughout the world, providing electricity, natural gas and water, are pursuing SmartGrid initiatives that represent one of the more mature examples of SAE. We have s...
    The security devil is always in the details of the attack: the ones you've endured, the ones you prepare yourself to fend off, and the ones that, you fear, will catch you completely unaware and defenseless. The Internet of Things (IoT) is nothing if not an endless proliferation of details. It's the vision of a world in which continuous Internet connectivity and addressability is embedded into a growing range of human artifacts, into the natural world, and even into our smartphones, appliances, and physical persons. In the IoT vision, every new "thing" - sensor, actuator, data source, data con...
    The Internet of Things is tied together with a thin strand that is known as time. Coincidentally, at the core of nearly all data analytics is a timestamp. When working with time series data there are a few core principles that everyone should consider, especially across datasets where time is the common boundary. In his session at Internet of @ThingsExpo, Jim Scott, Director of Enterprise Strategy & Architecture at MapR Technologies, discussed single-value, geo-spatial, and log time series data. By focusing on enterprise applications and the data center, he will use OpenTSDB as an example t...
    How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it's a mix of architectural styles ...
    An entirely new security model is needed for the Internet of Things, or is it? Can we save some old and tested controls for this new and different environment? In his session at @ThingsExpo, New York's at the Javits Center, Davi Ottenheimer, EMC Senior Director of Trust, reviewed hands-on lessons with IoT devices and reveal a new risk balance you might not expect. Davi Ottenheimer, EMC Senior Director of Trust, has more than nineteen years' experience managing global security operations and assessments, including a decade of leading incident response and digital forensics. He is co-author of t...
    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 @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, discussed 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!
    The Internet of Things will put IT to its ultimate test by creating infinite new opportunities to digitize products and services, generate and analyze new data to improve customer satisfaction, and discover new ways to gain a competitive advantage across nearly every industry. In order to help corporate business units to capitalize on the rapidly evolving IoT opportunities, IT must stand up to a new set of challenges. In his session at @ThingsExpo, Jeff Kaplan, Managing Director of THINKstrategies, will examine why IT must finally fulfill its role in support of its SBUs or face a new round of...
    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, described 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.
    Enthusiasm for the Internet of Things has reached an all-time high. In 2013 alone, venture capitalists spent more than $1 billion dollars investing in the IoT space. With "smart" appliances and devices, IoT covers wearable smart devices, cloud services to hardware companies. Nest, a Google company, detects temperatures inside homes and automatically adjusts it by tracking its user's habit. These technologies are quickly developing and with it come challenges such as bridging infrastructure gaps, abiding by privacy concerns and making the concept a reality. These challenges can't be addressed w...
    The Domain Name Service (DNS) is one of the most important components in networking infrastructure, enabling users and services to access applications by translating URLs (names) into IP addresses (numbers). Because every icon and URL and all embedded content on a website requires a DNS lookup loading complex sites necessitates hundreds of DNS queries. In addition, as more internet-enabled ‘Things' get connected, people will rely on DNS to name and find their fridges, toasters and toilets. According to a recent IDG Research Services Survey this rate of traffic will only grow. What's driving t...
    Scott Jenson leads a project called The Physical Web within the Chrome team at Google. Project members are working to take the scalability and openness of the web and use it to talk to the exponentially exploding range of smart devices. Nearly every company today working on the IoT comes up with the same basic solution: use my server and you'll be fine. But if we really believe there will be trillions of these devices, that just can't scale. We need a system that is open a scalable and by using the URL as a basic building block, we open this up and get the same resilience that the web enjoys.
    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, examined 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 is e...
    We are reaching the end of the beginning with WebRTC, and real systems using this technology have begun to appear. One challenge that faces every WebRTC deployment (in some form or another) is identity management. For example, if you have an existing service – possibly built on a variety of different PaaS/SaaS offerings – and you want to add real-time communications you are faced with a challenge relating to user management, authentication, authorization, and validation. Service providers will want to use their existing identities, but these will have credentials already that are (hopefully) i...
    "Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
    P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at @ThingsExpo, Robin Raymond, Chief Architect at Hookflash, will walk through the shifting landscape of traditional telephone and voice services ...
    Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at Internet of @ThingsExpo, James Kirkland, Chief Architect for the Internet of Things and Intelligent Systems at Red Hat, described how to revolutioniz...
    Bit6 today issued a challenge to the technology community implementing Web Real Time Communication (WebRTC). To leap beyond WebRTC’s significant limitations and fully leverage its underlying value to accelerate innovation, application developers need to consider the entire communications ecosystem.
    The definition of IoT is not new, in fact it’s been around for over a decade. What has changed is the public's awareness that the technology we use on a daily basis has caught up on the vision of an always on, always connected world. If you look into the details of what comprises the IoT, you’ll see that it includes everything from cloud computing, Big Data analytics, “Things,” Web communication, applications, network, storage, etc. It is essentially including everything connected online from hardware to software, or as we like to say, it’s an Internet of many different things. The difference ...
    Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world.