Reader X emailed me earlier this week with an interesting problem. He was looking into building a class scheduling system but wanted a way to hande time conflicts on the client. He was currently making use of Flash Forms (which I strongly urge everyone to avoid) but wanted to switch to a pure HTML/JavaScript solution instead. I built up the following demo as one possible way to solve the problem. As always, comments and suggestions are welcome, but remember that this is mainly a proof of concept.

To begin, I'm going to create an Application.cfc file that will create a static list of classes. I've intentionally creates a set of classes that are one hour long as well as another list of two hour classes. This will create two simulateneous set of classes and force a situation where we need to check for conflicts.

component { = "classes test"; this.sessionManagement = true;

public boolean function onApplicationStart(){ //hard coded static data var data = []; data[1] = { id=1, name="Class A", start="2/14/2009 8:00 AM", end="2/14/2009 9:00 AM" }; data[2] = { id=2, name="Class B", start="2/14/2009 9:15 AM", end="2/14/2009 10:15 AM" }; data[3] = { id=3, name="Class C", start="2/14/2009 10:30 AM", end="2/14/2009 11:30 AM" }; data[4] = { id=4, name="Class D", start="2/14/2009 11:45 AM", end="2/14/2009 12:45 PM" }; data[5] = { id=5, name="Class E", start="2/14/2009 1:00 PM", end="2/14/2009 2:00 PM" }; data[6] = { id=6, name="Class F", start="2/14/2009 2:15 PM", end="2/14/2009 3:15 PM" }; data[7] = { id=7, name="Class G", start="2/14/2009 3:30 PM", end="2/14/2009 4:30 PM" };

data[8] = { id=8, name="Class AA", start="2/14/2009 8:00 AM", end="2/14/2009 10:00 AM" }; data[9] = { id=9, name="Class BB", start="2/14/2009 10:15 AM", end="2/14/2009 12:15 PM" }; data[10] = { id=10, name="Class CC", start="2/14/2009 12:30 PM", end="2/14/2009 2:30 PM" }; data[11] = { id=11, name="Class DD", start="2/14/2009 2:45 PM", end="2/14/2009 4:45 PM" };

application.classes = data; return true; }

public boolean function onRequestStart(string req) { if(structKeyExists(url, "init")) { onApplicationStart(); onSessionStart(); } return true; }

public boolean function onSessionStart() { session.classes = []; return true; }


Notice that I've also used the onSessionStart method to initialize an array for the user's selected classes. Now let's move to the front end. I began with a simple design that contained a drop down of classes a user could add, a list of currently selected users, and a third block that was used for debugging purposes.

<h2>Add Class</h2> <form id="addclass"> <select id="classlistSelector"> <cfloop index="c" array="#application.classes#"> <cfoutput><option value=""> (#c.start# - #c.end#)</option></cfoutput> </cfloop> </select> <input type="button" id="addButton" value="Add Class"> </form>

<h2>Your Classes</h2> <div id="classlist"></div>

<p> <a href="index.cfm?init=true">Restart</a> </p> <cfdump var="#application#" label="Application" expand="false"> <cfdump var="#session#" label="Session" expand="false">

For the most part this should be pretty vanilla. You see me making use of the class list on top. I've got a blank div for my class list. We're going to take care of that next. All the bits are here - so now it's time to look at some jQuery that will handle making this work.

<script> function displayMyClasses() { var myclasses = $.getJSON("classes.cfc?method=getmyclasses&returnformat=json", {}, function(data) { var s = "" for(var i=0; i < data.length; i++) {$ s += "<p><b>" + data[i].NAME + "</b><br/>" s += data[i].START + " to " + data[i].END s += "</p>" } $("#classlist").html(s) }) }

$(document).ready(function() {


$("#addButton").click(function() { //get the value of the class var classid = $("#classlistSelector option:selected").val() //now try to add it $.getJSON("classes.cfc?method=addclass&returnformat=json", {classid:classid}, function(data) { if(data == true) displayMyClasses() else alert("Sorry, there is a time conflict with that class!") }) }) }) </script>

There are two main functions here. First, my document.ready block (I tend to assume my readers all use jQuery, which isn't fair, so just consider that block as a 'When I'm done, do this' block) and a displayMyClasses function. Let's focus on the document.ready area first. It begins by calling displayMyClasses. We will discuss that next. It then adds a listener for the button we had in our form. This will handle getting the selected item from the select tag and passing it to a CFC. This CFC will return true or false depending on if we were able to add the class. On a successful add, we just redraw the selected classes. On a failure we use an alert. (Let me just add - I freaking hate alerts. But for now it is a quick and dirty way to handle it.)

Going up a bit to displayMyClasses, you can see it calling the CFC again (which we will show next). It asks for the user's classes and simply displays it in HTML.

So far so good. For the final bit, let's open the CFC. This CFC is one big mess of bad - specifically I've got Application and Session variables in there. In a "properly architected application" this wouldn't be there, but I'd still be writing. Since the focus of this entry was on the front end, I felt it was good decision to make. That being said - here is the component:

component {

remote boolean function addClass(numeric classid) { //only add if I don't have it - return true just means ignore the re-add if(hasClass(arguments.classid)) return true;

if(!hasConflict(arguments.classid)) { arrayAppend(session.classes, arguments.classid); return true; } else { return false; }


public struct function getTheClass(numeric id) { var classes = getClasses(); for(var i=1; i <= arrayLen(classes); i++) { if(classes[i].id == return classes[i]; } }

public array function getClasses() { return application.classes; }

remote array function getMyClasses() { var result = []; for(var i=1; i <= arrayLen(application.classes); i++) { if(hasClass(application.classes[i].id)) arrayAppend(result, application.classes[i]); } return result; }

public boolean function hasClass(numeric id) { for(var i=1; i <= arrayLen(session.classes); i++) { if(session.classes[i] == return true; } return false; }

public boolean function hasConflict(numeric id) { var theclass = getTheClass(;

var myclasses = getMyClasses(); for(var i=1; i <= arrayLen(myclasses); i++) { //same start time? if(dateCompare(myclasses[i].start, theclass.start) == 0) return true; //is the start time before my start and end after my start? if(dateCompare(myclasses[i].start, theclass.start) == -1 && dateCompare(myclasses[i].end, theclass.start) == 1) return true; //does my new class end after the start of my class and also begin before the end? if(dateCompare(myclasses[i].start, theclass.start) == 1 && dateCompare(myclasses[i].start, theclass.end) == -1) return true;
} return false; }


There's a bunch of functions here - but most are pretty trivial, like getClasses and getTheClass. Both of these would use SQL/ORM instead of what I have here, but again, it's just a demo. The critical function is addClass. The logic is relatively simply - if we have the class already, silently fail. If we don't have a conflict, add it. I migrated the 'conflict' logic to it's own method in order to keep the logic simple.

hasConflict() uses 3 rules to determine if there is a conflict:

1) Do I have a class that starts at the same time as the one I want to add?

2) Do I have a class that starts before the one I want to add and ends after it begins?

3) Do I have a class that starts after the new one begins and ends before the new one ends?

There is a chance I may be missing something there. The good thing though is that if I do find a logic mistake, I can correct it here and keep addClass relatively simple.

You can play with a demo of this here:

So all in all - it works (until someone finds a bug :) but it's missing a few things that would make it nicer. First - the drop down should remove classes after you've added them. Sure the application just ignores a re-add, but it would be nice to make the list smaller. It would also be nice to default the list to classes you haven't added. If I reload the page then the drop down should only contain classes I haven't added. We can even go further - why not display a list of classes we can't add anymore because of conflicts? I'll explore these options and more in the next version.

p.s. I wrote this entry in Evernote, and when I pasted it in, my code blocks got a bit fubared. First I lost all my line breaks. I fixed that by emailing myself the note. However, when I pasted in from the email I seemed to have lost my tabbing. Please forgive the format of the samples above.