Rails modeling and inspection tools are rare. Based on the fact that Rdoc didn't handle the RoR models associations or "content columns" to his liking, and that other Rubyforge modeling projects don't handle complex systems, Javier Smaldone decided to do his own. He recently released RailRoad 0.3.2. It generates class diagrams from Ruby on Rails applications as DOT graphs. You'll then need tools like Graphviz, or SpringGraph to transform the DOT files into image output.
Javier is planning to add some options intended to deal with "large" applications (diagram clusters for modules, exclude some classes, etc.). It will be interesting to see how the project evolves in regard to Javier's responsiveness to feature requests.
RailRoad can produce:
Model diagrams, showing both inheritance hierarchy and models associations. You can choose to show the model "content columns" and its types.The graphics generated don't look like UML but are closer to BON. The documentation comes with examples of complex models from Rails applications like Typo or rTPlan.
Controller diagrams, showing inheritance hierarchy. You can include the controllers' methods, grouped by its visibility (public, protected, private.)
Javier is planning to add some options intended to deal with "large" applications (diagram clusters for modules, exclude some classes, etc.). It will be interesting to see how the project evolves in regard to Javier's responsiveness to feature requests.
