Welcome!

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

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 IoT is changing the way enterprises conduct business. In his session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, discuss how businesses can gain an edge over competitors by empowering consumers to take control through IoT. We'll cite examples such as a Washington, D.C.-based sports club that leveraged IoT and the cloud to develop a comprehensive booking system. He'll also highlight how IoT can revitalize and restore outdated business models, making them profitable...
    In his session at 18th Cloud Expo, Bruce Swann, Senior Product Marketing Manager at Adobe, will discuss how the Adobe Marketing Cloud can help marketers embrace opportunities for personalized, relevant and real-time customer engagement across offline (direct mail, point of sale, call center) and digital (email, website, SMS, mobile apps, social networks, connected objects). Bruce Swann has more than 15 years of experience working with digital marketing disciplines like web analytics, social med...
    IoT generates lots of temporal data. But how do you unlock its value? How do you coordinate the diverse moving parts that must come together when developing your IoT product? What are the key challenges addressed by Data as a Service? How does cloud computing underlie and connect the notions of Digital and DevOps What is the impact of the API economy? What is the business imperative for Cognitive Computing? Get all these questions and hundreds more like them answered at the 18th Cloud Expo...
    SYS-CON Events announced today that ContentMX, the marketing technology and services company with a singular mission to increase engagement and drive more conversations for enterprise, channel and SMB technology marketers, has been named “Sponsor & Exhibitor Lounge Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York City, New York. “CloudExpo is a great opportunity to start a conversation with new prospects, but what happens after the...
    SYS-CON Events announced today the How to Create Angular 2 Clients for the Cloud Workshop, being held June 7, 2016, in conjunction with 18th Cloud Expo | @ThingsExpo, at the Javits Center in New York, NY. Angular 2 is a complete re-write of the popular framework AngularJS. Programming in Angular 2 is greatly simplified. Now it’s a component-based well-performing framework. The immersive one-day workshop led by Yakov Fain, a Java Champion and a co-founder of the IT consultancy Farata Systems and...
    Customer experience has become a competitive differentiator for companies, and it’s imperative that brands seamlessly connect the customer journey across all platforms. With the continued explosion of IoT, join us for a look at how to build a winning digital foundation in the connected era – today and in the future. In his session at @ThingsExpo, Chris Nguyen, Group Product Marketing Manager at Adobe, will discuss how to successfully leverage mobile, rapidly deploy content, capture real-time d...
    SYS-CON Events announced today that BMC Software has been named "Siver Sponsor" of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. BMC is a global leader in innovative software solutions that help businesses transform into digital enterprises for the ultimate competitive advantage. BMC Digital Enterprise Management is a set of innovative IT solutions designed to make digital business fast, seamless, and optimized from mainframe to mo...
    What a difference a year makes. Organizations aren’t just talking about IoT possibilities, it is now baked into their core business strategy. With IoT, billions of devices generating data from different companies on different networks around the globe need to interact. From efficiency to better customer insights to completely new business models, IoT will turn traditional business models upside down. In the new customer-centric age, the key to success is delivering critical services and apps wit...
    Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
    In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, will provide an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life ...
    SYS-CON Events announced today that MobiDev will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex software systems for startups and enterprises. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 200 develope...
    SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from Web startups to global enterprises. SoftLayer's modular architecture, full-featured API, and sophisticated automation provide unparalleled performance and control. Its flexible unified platform seamlessly spans physical and virtual devices linked via a world...
    Companies can harness IoT and predictive analytics to sustain business continuity; predict and manage site performance during emergencies; minimize expensive reactive maintenance; and forecast equipment and maintenance budgets and expenditures. Providing cost-effective, uninterrupted service is challenging, particularly for organizations with geographically dispersed operations.
    SYS-CON Events announced today TechTarget has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. TechTarget is the Web’s leading destination for serious technology buyers researching and making enterprise technology decisions. Its extensive global networ...
    SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
    SYS-CON Events announced today Object Management Group® has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
    As cloud and storage projections continue to rise, the number of organizations moving to the cloud is escalating and it is clear cloud storage is here to stay. However, is it secure? Data is the lifeblood for government entities, countries, cloud service providers and enterprises alike and losing or exposing that data can have disastrous results. There are new concepts for data storage on the horizon that will deliver secure solutions for storing and moving sensitive data around the world. ...
    SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. 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. For more information, please visit https://www.mangoapps.com/.
    The essence of data analysis involves setting up data pipelines that consist of several operations that are chained together – starting from data collection, data quality checks, data integration, data analysis and data visualization (including the setting up of interaction paths in that visualization). In our opinion, the challenges stem from the technology diversity at each stage of the data pipeline as well as the lack of process around the analysis.
    The IoTs 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, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...