Ruby and Rails and all that stuff

At the suggestion of a recruiter, I'm learning Ruby on Rails this weekend. I was active on the comp.lang.python mailing list when Matz came around talking about Ruby. It seemed like a good thing, but I mostly ignored Ruby for years because it seemed to be solving problems that I already had solutions for with Python. Likewise, Rails seemed to retread the same ground already covered by Django.

Motivated to take another look because of the wild popularity of Rails, I see there's something in Ruby that deserves attention, which is blocks (anonymous closures, or what Lispers would call lambda expressions). They function as closures, and any language that makes a closure a first-class object is a good language. There are a ton of good Ruby tutorials. I myself am partial to Ruby in Twenty Minutes. There are also a good Rails tutorial (and I'm sure there are several others). Another notable thing in the Ruby community is RDoc, an unusually good documentation tool.

I'll be installing Ruby and Rails on an Ubuntu 12.04 machine. I don't like how old the packages are in the official Ubuntu repository, so I'll install from Ruby websites instead. The first thing to do is install RVM with these two commands:

$ curl -L https://get.rvm.io | bash -s stable --ruby

$ source /home/wware/.rvm/scripts/rvm
Later I reversed my decision about the official repositories, when I discovered I could install "ruby1.9.3". What RVM offers is an ability to run multiple Ruby environments on the same machine, like Python's virtualenv.

So now Ruby is installed and you can type "irb" to begin an interactive Ruby session. Next install Rails, and some additional things you'll need soon:

$ gem install -V rails

$ sudo apt-get install libsqlite3-dev nodejs nodejs-dev

Now you can jump to step 3.2 of the Rails tutorial and you should be good to go. Or you can go to the Github repository (README) which I cloned from the railsforzombies.org folks, and that's where I'm going to be tinkering for a while.

When debugging Rails controller code, you'll want to uncomment "gem debugger" in Gemfile, insert "debugger" into your code, and then reload the page in your browser, and it will stop the development server and put you into an interactive shell with all the variables available in mid-process. You'll also have GDB commands like "step", "next", "continue", and breakpoints.

When you're ready to deploy, consider Heroku, a Rails hosting service that lets you use one virtual machine for free. I've deployed my Zombie Twitter app there, and after a few initial bumps, things have gone pretty smoothly.

Here's a custom search for Ruby and Rails:

All web app frameworks lead to Rome

Earlier I blogged about how it seemed like web app development had just zoomed past me. Since then, I've buckled down and actually started to study this stuff. My earlier posting only talked about the presentation layer, HTML, Javascript, and CSS. I still have more to learn about those, but the really interesting stuff happens on the server.

In December I went to a two-day session on Hibernate and Spring, and it was full of mysterious jargon that made me sleepy: dependency injection, inversion of control, aspects, object-relational mapping, convention over configuration, blah blah blah. I kept at it, though, looking at Rails and later Django. I'm now waist-deep in building a MySQL-backed Django site. What I learned is that (A) all these web app frameworks are remarkably similar to one another, and (B) those jargon terms are a lot simpler than they seem.

Inversion of control means that the framework makes calls into your app code, rather than you calling the framework from a main() function. Dependency injection is a set of tricks to minimize dependencies between different Java source files. Aspects are Java tricks that you can do by wrapping your methods in other methods with the same signatures, a lot like decorators in Python. Object-relational mapping is creating classes to represent your DB tables: each instance represents a row, each column is represented by a setter and getter. The MVC pattern gives the lay of the land for all these frameworks, and all the presentation stuff I talked about before is limited to the "view" piece.

As I find my footing in the basics, I start to notice where the interesting bits of more advanced topics pop up. If I put a Django app and a Mediawiki on the same server, can I do a single sign-on for both of them? I think I can, by writing an AuthPlugin extension to make the Mediawiki accept Django's authentication cookie.

Don't ask Django to serve a PHP page because it doesn't include a PHP interpreter (what mod_php does for Apache). Your Apache config file must deal with PHP files before routing to Django.

    AliasMatch /([^/]*\.php) ..../phpdir/$1
    WSGIScriptAlias / ..../djangodir/django.wsgi

One thing I haven't quite understood is why the Django community seems to love Prototype and hate jQuery. Is that just because Prototype is included in the standard Django package? Is it purely historical, with jQuery the abandoned but superior Betamax to Prototype's VHS?