ObjectiveResource is an Objective-C port of Ruby on Rails’ ActiveResource. It provides a way to serialize objects to and from Rails’ standard RESTful web-services (via XML or JSON) and handles much of the complexity involved with invoking web-services of any language from the iPhone.
I’ve had a chance to play with it this weekend and have found it to be pretty easy to work with. The developers of Objective Resource have created a pretty good Getting Started Guide you can follow, or you can watch a screencast of it as well. They even offer an example project for you to work with that gives you both the iPhone app (via Xcode) and the Rails app so you can see how everything works together.
One thing the example project does not include is accessing a Rails app that has authentication. Of course I was thinking I was all setup for this, but soon realized that I did not add my Active Resource functions in so that my app would work with XML/JSON requests. Luckily, while I was out in Denver, CO for iPhone Development Training (by Pragmatic Studio) I was able to get my hands on a copy of Advanced Rails Recipes by Mike Clark. I was extremely pleased that Mike graciously gave me the copy he had laying there for free. The particular recipe in the book that helped me was the Authenticate REST Clients. After I rewrote my authentication piece of my Rails app, I was getting data back and into my iPhone app. It was a very good feeling!
I thought I would include the screencast that the Objective Resource developers created. It runs about 6 minutes and is definitely worth a watch if you are looking at using Objective Resource for your next iPhone app backed by a Rails app.