Chicken Scratches

Welcome to the third part in my series of posts about creating a Facebook application. I am using Django as my web development framework, and this post will focus on some of the backend techniques I have worked out to make this work easier. This is not a tutorial, but a set of tools that I have developed. This is a long post, with a lot of source code; I hope you find at least some of it useful.

Keep in mind as you read this that the Facebook platform is still very new, and likely to change. In fact, if you're a FB user, you are probably aware they recently completed a major transition to a new profile design. This included many changes behind the scenes for developers, some of which are still playing out. I recommend keeping up with the Facebook Platform Developer Forum and the Facebook Developer Blog.

Also, I will assume you have already read the API Documentation and the documentation for PyFacebook, and that you know how to create a web app using Django. If not, you will want to start there.

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Welcome to the second part in my series of posts about creating a Facebook application. I am using Django as my web development framework, but this post doesn't have much to do with Django, since it deals with the front end. In particular, it talks about how to write JavaScript that can work both in and out of Facebook.

As I mentioned last time, Facebook lets developers use a subset of JavaScript, which they call FBJS. The FBJS is transformed on the fly into JavaScript as the page is loaded. All variables and functions you define or reference are prepended with a string like "a123456789_", including calls to document.getElementById and setTimer and the like. This is done in order to restrict what you can do with DOM elements, to avoid cross-site-scripting attacks and unwanted user-hostile behavior. FBJS is fairly well documented, so if you plan to do some Facebook JavaScript development, you should start there.

The biggest restriction that FBJS imposes is that you can no longer access the attributes of DOM elements directly, but must go through an abstraction API consisting of a series of setters and getters. For example, instead of saying something like imageEl.src = myImageUrl, you instead need to call imageEl.setSrc(myImageUrl).

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Facebook made a splash a year or two ago when they opened up their API. Now developers could write applications that integrate with the site. Instantly, users -- many of whom had fled to Facebook from a spam-filled MySpace -- were inundated with Requests to battle ninjas and News Items bearing obscene pictures. To Facebook's credit, they did clamp down and put some restrictions on what apps can do. A few entertaining or useful applications have risen to the top, and the potential of the API is ready to be exploited. It's not an easy task for a developer, however. In the next few Chicken Scratches posts, I'll talk about my experience developing two Facebook apps from scratch: The Limerick Book, a site that works both in and outside of Facebook and allows users to share and rate Limericks, and Play Scopa, a traditional Italian card game that users can play against each other in realtime (this one is not yet launched to the public). This first post discusses some of the difficulties I have run into. In the next couple posts, I'll discuss how I dealt with them. First, to set the scene:

My setup

I am using the Django web framework for my backend development, the latest SVN version running with Python version 2.4 on a shared host at Dreamhost. In fact, it's the same server I use for this site and weblog. To connect Django to Facebook, I am using the nice PyFacebook library, which is pretty mature, though I had to modify the code to support some of the latest features of the Facebook API. And now, on to the perils. Read the rest of this entry »