RESTful Goodness - I declare!

Rails 1.2 was recently released, and I've been updating and upgrading Pikaplanner to take advantage of some of the new features in 1.2.

The highlight of Rails 1.2 is built-in REST support, and I've been updating my controllers to provide what amounts to a standard, easy-to use, web-services API.

My first step in the process was to work through some of the examples in Rob Orsini's terrific developer volume Rails Cookbook. Diego Scataglini's examples in Rob's book provide a simple and quick intro to REST support in Rails 1.2.

REST is a great example of Clayton Christensen's concept of a disruptive technology. I've worked with SOAP and RPC in the past, and at first blush REST is less powerful than either. Still, with Rails, REST is easy and cheap to adopt at the service-provider end, and easy to experiment with at the receiver end.

For example, one of the first code areas I worked through was a simple product listing. The goal here is to provide both a web (HTML) and web services (XML) interface to our (sample) product information.

The REST support in Rails makes it easy, and all we need to do to turn our web pages into a web-services interface is tell (though the URL) our application that we want XML (instead of HTML) back.

So: to see the web page listing our products, we'd use "/products", as shown below:

So far, so good, so common -- in Rails we've called up pages like this in the ":controller/:action/:id" form (that defaults to a GET on index.html here) zillions of times. What's new, with REST and Rails 1.2, is that all we have to do to have a web services interface is tell the application we want XML back, instead of HTML. So our URL is of the form ":controller/:action/:id.xml", as shown below:

and as you can see we get XML back - a web services interface practically for free (developer time-wise).

There is a lot of magic underlying this simple example, but a handful of key points stand out:

1) All we need for our "web services" interface is to tell our controller we want XML back.

2) We could have gotten JavaScript back (where that is appropriate) in the same manner

3) The key shift in development mindset is that the interface is not imperative (as SOAP and most web services are) but declarative -- everything important in the system a) has its own URL for CRUD access, b) exists as a stateless resource, in which complex actions can be created by changes in state of one resource triggering actions to change the state of other, related resources, and 3) is capable of varying the format of responses, depending on what is requested.

That third point is a mouthful, and the core of stuff on which theses have been written.

Declarative programming is a significant mind-shift, one I'll be writing more about in the future.