Being RESTful and avoiding redundancy question

[akiryk]

I've been reading about building RESTful applications and it sounds like a good approach that I want to use (great overview: http://softiesonrails.com/2007/3/28/...ding-resources )

Question: how do I avoid redundancy if I have several controllers that do similar but slightly distinct things?

For example, let's say I'm building a forum site with 2 categories: music and cars. People can click on the "music" tab to see discussions and add comments about music; they can click on the "cars" tab for discussions about cars.

I create a model called Discussion and two controllers -- carDiscussion_controller and musicDiscussion_controller. Each controller has the standard 7 RESTful methods (index, show, new, edit, update, create, destroy). Thus, the index method of musicDiscussion could be customized to list only discussions related to music.

This seems good and maybe it is, but I'm afraid there will some redundancy. For example, the destroy method will always do the same thing -- destroy a discussion. Is this a problem? Is there a better way to do this?

[Fenrir2]

Just create one DiscussionConrtroller.

Create special actions like:

your-site.com/discussions/music
your-site.com/discussions/cars

That list discussions about music and cars.

[akiryk]

Are you saying that in addition to methods like index and show, I'd have a method named music in DiscussionController? The music method would, say, list all the discussions in the music topic.
Wouldn't this be non-RESTful? Does that matter?

[Fenrir2]

Yes, you could do that. I think this is RESTful. You can do this without adding extra actions too:

your-site.com/discussions?topic=music
your-site.com/discussions?topic=cars

You can extract the topic like this:

class DiscussionController < ApplicationController
  def index
     topic = params[:topic]
     if topic
       @discussions = Discussion.find_by_topic(topic)
     else
       @discussions = Discussion.find(:all)
     end
   end
 
   ...
end

You could also use the more Rails-like way: add an extra model Topic.

class Topic < ActiveRecord::Base
  has_many :discussions
end

Now create a TopicController, and add a nested route:

map.resources :topics do |topics|
  topics.resources :discussions
end

This gives you these urls:

your-site.com/topics/[the-topic]/discussions

This presentation is interesting: http://media.rubyonrails.org/present...fresources.pdf
Video: http://www.scribemedia.org/2006/07/09/dhh/

[akiryk]

Cool -- these links look great.

I also found a document from March 2007 called RESTful RAILS Development by Wirdemann and Baustert:
http://www.b-simple.de/documents
It agrees with your recommendation above to use a nested route. This makes a lot of sense -- a Topic has many discussions. When a user views or manipulates a discussion, it should be in the context of a topic. One thing I hadn't realized, however, is that my generated controller won't know that it is responsible for a nested resource. Thus, the index action of my DiscussionsController would have to be changed to look like this:

def index
	topic = Topic.find(params[:topic_id])
	@discussions = topic.discussions.find(:all)
	…
end

(ReggieB in this forum recommended I follow this strategy a few days ago, but I didn't understand it the first time; now I think I do).

One syntax question: why not make topic an instance variable? (as in topic = Topic.find(params[:topic_id])
Is it simply considered a local variable?

[Fenrir2]

If you don't need it in the view then it's better to use a local variable: you don't clutter your namespace this way.

Your code is not as efficient as it could be: you're executing two SQL selects, but it can be done with one:

def index
  @discussions = Discussion.find_by_topic(params[:topic_id])
end

[akiryk]

If I wanted to list comments associated with a given discussion, would my show action would be something like the following?
def show
@comments = Comment.find_by_discussion(params[:discussion_id])
end

It doesn't like this: says "undefined method `find_by_discussion' for Comment:Class"

I say "has_many :comments" in Discussion class and "belongs_to :discussion" in Comment class.

[akiryk]

Actually, I think it should say find_by_discussion(params[:id]) -- but that doesn't work. Nor does what you suggested above for index -- although the inefficient code does work. What am I missing? Do I need to add a find_by_topic method to my model? I tried Discussion.find_by_topic_id as well, since my discussions table has a column called "topic_id"