Nesting resource - ruby-on-rails

Question

I'm trying to nest my messages controller into my channels controller. But when I go to my messages view i get the error "couldn't find channel with no id"
class MessagesController < ApplicationController
def index
#channel = Channel.find(params[:channel_id])
#messages = #channel.messages
end
def new
#channel = Channel.find(params[:channel_id])
#message = #channel.messages.build
end
def create
#channel = Channel.find(params[:channel_id])
#message = #channel.messages.build(params[:message])
if #message.save
flash[:notice] = "Successfully created message."
redirect_to channel_url(#message.channel_id)
else
render :action => 'new'
end
end
def edit
#message = Message.find(params[:id])
end
def update
#message = Message.find(params[:id])
if #message.update_attributes(params[:message])
flash[:notice] = "Successfully updated message."
redirect_to channel_url(#message.channel_id)
else
render :action => 'edit'
end
end
def destroy
#message = Message.find(params[:id])
#message.destroy
flash[:notice] = "Successfully destroyed message."
redirect_to channel_url(#message.channel_id)
end
end
Channels controller
class ChannelsController < ApplicationController
def index
#channels = Channel.find(:all)
end
def show
#channel = Channel.find(params[:id])
#message = Message.new(:channel => #channel)
end
def new
#channel = Channel.new
end
def create
#channel = Channel.new(params[:channel])
if #channel.save
flash[:notice] = "Successfully created channel."
redirect_to #channel
else
render :action => 'new'
end
end
def edit
#channel = Channel.find(params[:id])
end
def update
#channel = Channel.find(params[:id])
if #channel.update_attributes(params[:channel])
flash[:notice] = "Successfully updated channel."
redirect_to #channel
else
render :action => 'edit'
end
end
def destroy
#channel = Channel.find(params[:id])
#channel.destroy
flash[:notice] = "Successfully destroyed channel."
redirect_to channels_url
end
end
routes.rb
SeniorProject::Application.routes.draw do
resources :users
resources :channels, :shallow => true do |channels|
channels.resources :messages
end
root :channels
resources :users, :user_sessions
match 'login' => 'user_sessions#new', :as => :login
match 'logout' => 'user_sessions#destroy', :as => :logout
match ':controller(/:action(/:id(.:format)))'
end

Answer 1

What's going on here is that this line:
#channel = Channel.find(params[:channel_id])
Is falling over because there's no defined channel_id in the params hash. I see you're using shallow routes, which means your uri probably looks like this:
/messages
And you need it to look like:
/channels/1/messages
Try changing your url to be:
channel_messages_url(#channel)
instead of
messages_url
This is a guess btw, it could be because of the way you've defined your routes.rb, which looks a little odd because you're defining the messages routes twice, once with the has_many and again as a proper resource. You probably want something like:
# assuming you need shallow routes
resources :channels, :shallow => true do |channels|
channels.resources :messages
end