Beginner Tutorial: Hello World
In this tutorial, we'll be writing a simple application to make sure we have Wheels installed properly and that everything is working as it should. Along the way, you'll get to know some basics about how applications built on top of Wheels work.
Testing Your Install
Let's make sure we're all on the same page. I'm going to assume that you've already downloaded the latest version of Wheels and have it installed on your system. If you haven't done that, stop and read the Installation chapter and get everything setup. It's okay, this web page will wait for you.
Okay, so you have Wheels installed and can see the Wheels "Congratulations!" page as shown in Figure 1 below. That wasn't that hard now, was it?
Figure 1: Wheels congratulations screen.
Hello World: Your First Wheels App
Okay, let's get to some example code. We know that you've been dying to get your hands on some code!
To continue with Programming Tutorial Tradition, we'll create the ubiquitous Hello World! application. But to keep things interesting, let's add a little Wheels magic along the way.
Setting up the Controller
Let's create a controller from scratch to illustrate how easy it is to set up a controller and plug it into the Wheels framework.
First, create a file called Say.cfc in the controllers directory and add the code below to the file.
Congratulations, you just created your first Wheels controller! What does this controller do, you might ask? Well, to be honest, not much. It has no functions defined so it doesn't add any new functionality to our Wheels application. But because it extends the base Controller component, it inherits quite a bit of powerful functionality and is now tied into our Wheels application.
So what happens if we try to call our new controller right now? Lets take a look! Open your browser and point your browser to the new controller. Because my server is installed on port 80, my URL is http://cfwheels.1.0/index.cfm/say. You may need to enter a different URL, depending on how your web server is configured. In my case, I will be using the host name cfwheels.1.0, so my URL will look like:
If you did everything right, you will get the Wheels error shown below in Figure 2. (Ironic that getting an error is doing something right, huh? Don't get used to it, buddy!)
Figure 2: Wheels error after setting up your blank say controller.
The error says "Could not find the view page for the 'index' action in the 'say' controller." Where did "index" come from? The URL we typed in only specified a controller name but no action. When an action is not specified in the URL, Wheels assumes that we want the default action. Out of the box, the default action in Wheels is set to
index. So in our example, Wheels tried to find the
index action within the
say controller, and it threw an error because it couldn't find its view page.
Setting up an Action
But let's jump ahead. Now that we have the controller created, let's add an action to it called hello. Change your say controller so it looks like the code block below:
As you can see, we created an empty method named hello.
Now let's call our new action in the browser and see what we get. To call the
hello action we simply add /hello to the end of the previous URL that we used to call our
Once again, we get a ColdFusion error. Although we have created the controller and added the
hello action to it, we haven't created the view.
Setting up the View
By default, when an action is called, Wheels will look for a view file with the same name as the action. It then hands off the processing to the view to display the user interface. In our case, Wheels tried to find a view file for our say/hello action and couldn't find one.
Let's remedy the situation and create a view file. View files are simple CFML pages that handle the output of our application. In most cases, views will return HTML code to the brower. By default, the view files will have the same name as our controller actions and will be grouped into a directory under the view directory. This new directory will have the same name as our controller.
Find the views directory in the root of your Wheels installation. There will be a few directories in there already. For now, we need to create a new directory in the views directory called say. This is the same name as the controller that we created above.
Now inside the say directory, create a file called hello.cfm. In the hello.cfm file, add the following line of code:
Save your hello.cfm file, and let's call our say/hello action once again. You have your first working Wheels page if your browser looks like Figure 3 below.
Figure 3: Your first working Wheels action.
You have just created your first functional Wheels page, albeit it is a very simple one. Pat yourself on the back, go grab a snack, and when you're ready, let's go on and extend the functionality of our Hello World! application a little more.
Adding Dynamic Content to Your View
We will add some simple dynamic content to our
hello action and add a second action to the application. We'll then use some Wheels code to tie the 2 actions together. Let's get get to it!
The Dynamic Content
The first thing we are going to do is to add some dynamic content to our say/hello action. Modify your say controller so it looks like the code block below:
<cfset time = Now()>
All we are doing here is creating a variable called time and setting its value to the current server time using the basic ColdFusion
Now() function. When we do this, the variable becomes immediately available to our view code.
Why not just set up this value directly in the view? If you think about it, maybe the logic behind the value of
time may eventually change. What if eventually we want to display its value based on the user's time zone? What if later we decide to pull it from a web service instead? Remember, the controller is supposed to coordinate all of the data and business logic, not the view.
Displaying the Dynamic Content
Next, we will modify our say/hello.cfm view file so that it looks like the code block bellow. When we do this, the value will be displayed in the browser.
<p>Current time: <cfoutput>#time#</cfoutput></p>
Now call your say/hello action again in your browser. Your browser should look like Figure 4 below.
Figure 4: Hello World with the current date and time.
This simple example showed that any dynamic content created in a controller action is available to the corresponding view file. In our application, we created a
time variable in the say/hello controller action and display that variable in our say/hello.cfm view file.
Adding a Second Action: Goodbye
Now we will expand the functionality of our application once again by adding a second action to our
say controller. If you feel adventurous, go ahead and add a goodbye action to the say controller on your own, then create a goodbye.cfm view file that displays a "Goodbye" message to the user. If you're not feeling that adventurous, we'll quickly go step by step.
First, modify the the
say controller file so that it looks like the code block below.
<cfset time = Now()>
Now go to the view/say directory and create a goodbye.cfm page.
Add the following code to the goodbye.cfm page and save it.
If we did everything right, we should be able to call the new say/goodbye action using the following URL:
Your browser should look like Figure 5 below:
Figure 3: Your new
Linking to Other Actions
Now let's link our two actions together. We will do this by adding a link to the bottom of each page so that it calls the other page.
Linking Hello to Goodbye
Open the say/hello.cfm view file. We are going to add a line of code to the end of this file so our say/hello.cfm view file looks like the code block below:
<p>Current time: <cfoutput>#time#</cfoutput></p>
<p>Time to say <cfoutput>#linkTo(text="goodbye", action="goodbye")#?</cfoutput></p>
linkTo() function is a built-in Wheels function. In this case, we are passing 2 named parameters to it. The first parameter,
text, is the text that will be displayed in the hyperlink. The second parameter,
action, defines the action to point the link to. By using this built-in function, your application's main URL may change, and even controllers and actions may get shifted around, but you won't suffer from the dreaded dead link. Wheels will always create a valid link for you as long as you configure it correctly when you make infrastructure changes to your application.
Once you have added the additional line of code to the end of the say/hello.cfm view file, save your file and call the say/hello action from your browser. Your browser should look like Figure 6 below.
Figure 6: Your say/hello action with a link to the
You can see that Wheels created a link for us and added an appropriate URL for the say/goodbye action to the link.
Linking Goodbye to Hello
Let's complete our little app and add a corresponding link to the bottom of our say/goodbye.cfm view page.
Open your say/goodbye.cfm view page and modify it so it looks like the code block below.
<p>Time to say <cfoutput>#linkTo(text="hello", action="hello")#?</cfoutput></p>
If you now call the say/goodbye action in your browser, your browser should look like Figure 7 below.
Figure 7: Your say/goodbye action with a link to the
Much More to Learn
You now know enough to be dangerous with ColdFusion on Wheels. Look out! But there are many more powerful features to cover. You may have noticed that we haven't even talked about the M in MVC.
No worries. We will get there. And we think you will enjoy it.