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

Implementing a Nested Set Model in ColdFusion

Building and using a flexible categorization system

When building applications, from content management to product catalogs, your project will typically be impacted by the method you choose for categorization. Designing code that is flexible enough to allow for ease of reuse, but simple enough to allow for ease of implementation, can often tie a developer in knots. The nested set model can help you fulfill both those goals.

This article will cover a simple implementation of this model, and draws extensively from two sources, Joe Celko's SQL for Smarties and Benjamin Elmore's Dynamic Publishing with ColdFusion MX. Both are recommended reading for a more in-depth look at the nested set model.

What Is the Nested Set Model?
In order to better understand the advantages of the nested set model in representing category trees within relational databases, we will first look at an alternate, commonly used method, the adjacency list model. The standard adjacency list model can be comprised of simply a categoryID, category, and parent field (see Figure 1).

 

Using the adjacency list model, a root node - a category that has no parent - is signified by a null value in the parent field (from here on out, node and category will often be used interchangeably). A leaf node is a category that has no children and can be determined through the use of a simple query. Determining the immediate parent or children of a given category also requires only a simple query. However, any function that would require traversing the tree beyond either the immediate parent or children of a given category would require complex recursive queries that are difficult to code, particularly when the depth of the tree is unknown. Similar problems occur when you wish to create functions for removing a sub tree. As adjacency list models are quite common, most experienced developers are well aware of their many deficiencies.

Rather than depend upon explicitly defined parents, the nested set model uses a set of left and right position integers to establish any given category's position within the tree structure. The left and right positions establish a range within which the left and right positions of any children will fall. The range between the left and right positions can easily be expanded to accommodate growth of the tree, and can be contracted just as easily when nodes are removed. In addition, determining the parents or children of a given node within a tree or even determining a given node's depth within the tree is a simple process regardless of the total depth of the tree.

In order to visualize this concept, let's take a root node (i.e., a node that has no parent) named "Macromedia," which is assigned the left and right positions of 1 and 20 respectively. A child of Macromedia called "ColdFusion" could have a left position of 2 and a right position of 9. Furthermore, a child of ColdFusion called "MX" could have a left position of 7 and a right position of 8, in which case it would be automatically recognizable as a leaf node given that the difference between the left and right positions is 1. See Figure 2 for a visual representation of a nested set model.

 

Building the CFC
Before I begin delving into the code of our component, I would first like to cover some assumptions I used in building it. Although the code is based upon examples from Dynamic Publishing with ColdFusion MX and SQL for Smarties, it has been modified in part to allow for compatibility with an Access database and also so that all public methods of the component return queries. While there are certainly benefits to using a more object-oriented approach within your components, and this component could be easily modified to meet that goal, I am choosing to return queries as I believe this makes the component easier to understand and implement for beginners and advanced users alike.

Before using this component, you first must create a table named "categories" in your database. If you are using Access, you would structure it as follows (see Figure 3):

 
  1. CategoryID is your primary key and has a data type of text with a field size of 40.
  2. Category has a data type of text with a field size of 255.
  3. Lpos has a data type of number and a field size of long integer.
  4. Rpos has a data type of number and a field size of long integer.
The first method of our component is called new (see Listing 1: categories.cfc)). This method is designed to simply create an empty query containing the columns defined within our table. A row is then inserted and a value set for categoryID, which is a ColdFusion UUID. When building components structured to return queries, I always add this method. The primary function of this method is to make it easier to build a form to update the database. Later we will cover building this form, at which time the purpose of this method will be more obvious.

The save method is fairly straightforward as it simply determines whether to call the Add or the Edit method depending on whether the categoryID sent already exists in the database.

The add, edit, and delete methods are fairly standard representations of their SQL counterparts (insert, update, and delete respectively), except for a few important points that we will cover. The first is that before a category is inserted, either the createRootNode or the createChildNode method must be called depending upon whether a parent category ID has been sent, keeping in mind that a root node is a node without a parent. We will discuss both methods in more detail later, but it is important to note that they both return a structure containing the left and right position integers.

Second, you should be aware that the edit method only allows changing of the text in the category field. This is because, as we discussed before, one of the few drawbacks of the nested set model is that it is extremely difficult to move a sub tree. Therefore, for simplicity's sake, this component simply disallows moving a category once it has been created.

Third, you will note a series of queries within the delete function called CloseGap 1, 2, 3, and 4. To understand the reason for these queries, you must first understand the logic behind including them, which is that, rather than delete a node (category) along with its entire subtree, I have chosen to promote the child nodes of any deleted node. For instance, let's take a category tree containing Grandpa Abe, which has a child, Homer; and Homer has three children, Bart, Lisa, and Maggie. Should something befall Homer, say an accident at the nuclear plant, Bart, Lisa, and Maggie would be adopted by Grandpa Abe. Thus the CloseGap queries are designed to do just that, close any gaps in the left and right position fields within the database, thereby promoting any children of the deleted node.

The get function within our component has been customized to implement a variety of different common queries required when integrating the category system into your site. This method takes four arguments: categoryID, children, parents, and immediate, all of which are optional. Due to the structure of the if statement, the Boolean argument children takes precedence over the Boolean argument parents. In addition, the Boolean argument immediate relates specifically to the children argument but is ignored otherwise. The method is as follows:

  • If children is true and a categoryID is supplied, then the component will retrieve the children of a given node
    -If immediate is true, only the immediate children are returned (i.e., one level below the level of a given node), otherwise all children are returned
  • If parents is true and a categoryID is supplied, then the component will return all parents of a given node
  • If only a categoryID is supplied, then only the information for the specific node is returned
  • If no arguments are supplied, then a raw query of all category data is returned
We will discuss later how this method is implemented within your application.

The getAllNodes method is a variation on the get method that returns all categories, with the difference being that getAllNodes returns a lvl column in the query that specifies the depth within the tree of any given node. For instance, given our example from earlier, the Bart category would have a value for lvl equal to 3, as it is three levels deep in the category tree. In addition, you can specify a lvl argument that will filter the returned results by a given depth. Again, using our previous example, specifying the value of 3 in the lvl argument would return only the categories of Bart, Lisa, and Maggie. Being able to retrieve the depth information for categories is a useful feature that you will find yourself using repeatedly throughout your application.

The remaining methods, createRootNode and createChildNode are both private methods, meaning they can only be called from inside the component. They are both designed to return the pos structure used within the add method as we saw earlier. The createChildNode method also updates the tree structure to make room for the node to be created.

Using the Component
Let's cover some basic implementations of the categories component by first looking at how to build a form to update the category tree. We will do this in the context of creating and organizing categories for Web site navigation. The form we will create is missing a lot of niceties, which I will leave for you to add at your leisure. For these examples to work, you must first create the database as explained earlier in this article and add that as a dsn within the ColdFusion administrator called CFDJ.

Our form is self-submitting and includes only two fields, one a text field to enter the name of the category and the other a select box to choose a parent category if applicable (see Listing 2: addCategories.cfm). The select box uses the lvl integer returned by the getAllNodes method to structure the list so that the depth within the category tree is visible (see Figure 4). The form is prefilled with either the value of a category determined by URL.categoryID or by the values returned by the new method, which is empty except for the categoryID. Note that when the form is prefilled with an existing category, the parent category select box is disabled because, as we discussed earlier, the component disallows changing the parent of an existing category.

 

When the form is submitted, we first run it through basic server-side error processing. Then we remove any empty values from the form structure so that they are not passed on to our component through the argumentCollection (this is simply a shortcut I prefer to use for submitting forms to a component). Finally, we call the save method, which, if you recall, determines whether the category should be added or edited.

Once submitted, you can view your category added to the tree within your select box, or view the test page, the basic code which I have also included (see Listing 3: index.cfm). The test page shows some standard uses for the different get methods within the component, such as getting the root level categories to propagate a category menu, getting the immediate children of a given category to propagate a submenu, and getting the parents of a given category to propagate breadcrumbs (see Figure 5). As you can see, all of these functions are exceedingly easy to use, as they require very little coding.

 

Conclusion
Using the nested set model, we have built a component and category structure that is flexible enough to use in a variety of applications with little to no modification. In addition, by abstracting this model into a component, we have made it portable enough to reuse relatively effortlessly.

More Stories By Brian Rinaldi

Brian Rinaldi, a member of the Editorial Board of CFDJ, is a web developer at Hasbro. He is also a member of the Adobe Community Experts program, the manager of the Boston ColdFusion User Group and an Advanced Certified ColdFusion MX Developer, as well as a Microsoft Certified Professional. Brian is most well known for his efforts promoting open-source projects in ColdFusion, especially for maintaining the ColdFusion open-source list as well as the weekly updates, both of which you can find via his web site at remotesynthesis.com.

Comments (1) View Comments

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.


Most Recent Comments
Abraham Lloyd 01/15/04 09:42:27 AM EST

Having worked quite a bit with this model in the past, one point to note is that this model should only be recommended for hierarchies that are static (never change) or that infrequently change. Inserting new nodes or moving nodes require that all elements in hierarchy that are affected be renumbered and ordered.

If you have a hierarchy that contains several hundred/thousand rows, this could result in every record in the hierarchy being updated (which clearly is less than ideal). If your hierarchies are static, however, then this model will scale and perform well under heavy load.

@ThingsExpo Stories
"My role is working with customers, helping them go through this digital transformation. I spend a lot of time talking to banks, big industries, manufacturers working through how they are integrating and transforming their IT platforms and moving them forward," explained William Morrish, General Manager Product Sales at Interoute, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
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.
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 business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
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...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. 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 - comp...
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...
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, will deep dive into best practices that will ensure a successful smart city journey.
SYS-CON Events announced today that 910Telecom 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. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long dev...
In today's uber-connected, consumer-centric, cloud-enabled, insights-driven, multi-device, global world, the focus of solutions has shifted from the product that is sold to the person who is buying the product or service. Enterprises have rebranded their business around the consumers of their products. The buyer is the person and the focus is not on the offering. The person is connected through multiple devices, wearables, at home, on the road, and in multiple locations, sometimes simultaneously...
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.
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, will discuss the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
Akana has announced the availability of version 8 of its API Management solution. The Akana Platform provides an end-to-end API Management solution for designing, implementing, securing, managing, monitoring, and publishing APIs. It is available as a SaaS platform, on-premises, and as a hybrid deployment. Version 8 introduces a lot of new functionality, all aimed at offering customers the richest API Management capabilities in a way that is easier than ever for API and app developers to use.
Personalization has long been the holy grail of marketing. Simply stated, communicate the most relevant offer to the right person and you will increase sales. To achieve this, you must understand the individual. Consequently, digital marketers developed many ways to gather and leverage customer information to deliver targeted experiences. In his session at @ThingsExpo, Lou Casal, Founder and Principal Consultant at Practicala, discussed how the Internet of Things (IoT) has accelerated our abil...
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
SYS-CON Events announced today that CDS Global Cloud, an Infrastructure as a Service 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. CDS Global Cloud is an IaaS (Infrastructure as a Service) provider specializing in solutions for e-commerce, internet gaming, online education and other internet applications. With a growing number of data centers and network points around the world, ...
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.