Why my code takes me to different URL? - ruby-on-rails

Question

First of all, My resource is nested using to_param for slug at Community model.
I'm at example.com/shop/walmart/topic/14/edit .
If I press update without captcha input, it obviously should take me back to edit page again with flash error message.
However it takes me to example.com/shop/14/topic/14/edit . <= it's taking the same parameter. it should take 'walmart' which is community_name for first argument, and :id for topic.
All the fields are set the same with what I typed in at the previous page.
How can I avoid this? it should redirect to the same url as previous page.
routes.rb
resources :communities, :path => "shops", do
resources :community_topics, :path => "topics"
end
controller
def simple_captcha_check
if !simple_captcha_valid?
flash[:error] = 'Wrong Captcha!'
if request.put? # We came from an edit request
#community_topic = CommunityTopic.find(params[:id])
#community_topic.attributes = params[:community_topic]
render :action => :edit
elsif request.post? # We came from a new request
#community_topic = CommunityTopic.new params[:community_topic]
render :action => :new
end
end
end
models/community.rb Note that I use slug here
def to_param
"#{community_name}"
end
views/community_topics/_form.html.erb
<%= form_for #community_topic, :html => { :class => 'form-horizontal' } do |f| %>
<div class="control-group">
<%= f.label :title, :class => 'control-label' %>
<div class="controls">
<%= f.text_field :title, :class => 'text_field' %>
</div>
</div>
<div class="control-group">
<%= f.label :body, :class => 'control-label' %>
<div class="controls">
<%= f.text_area :body, :class => 'text_area' %>
</div>
</div>
<div class="control-group">
<div class="controls">
<%= show_simple_captcha(:label => "human authentication") %>
</div>
</div>
<div class="form-actions">
<%= f.submit nil, :class => 'btn btn-primary' %>
<%= link_to t('.cancel', :default => t("helpers.links.cancel")),
community_topic_index_path, :class => 'btn' %>
</div>
<% end %>
rake routes | grep community_topic
community_community_topics GET /shops/:community_id/topics(.:format) community_topics#index
POST /shops/:community_id/topics(.:format) community_topics#create
new_community_community_topic GET /shops/:community_id/topics/new(.:format) community_topics#new
edit_community_community_topic GET /shops/:community_id/topics/:id/edit(.:format) community_topics#edit
community_community_topic GET /shops/:community_id/topics/:id(.:format) community_topics#show
PUT /shops/:community_id/topics/:id(.:format) community_topics#update
DELETE /shops/:community_id/topics/:id(.:format) community_topics#destroy
By the way, my index action in controller is just like this, and it's working fine!
community_topics_controller.rb #index
def index
#community = Community.find_by_community_name(params[:community_id])
#community_topics = #community.community_topics
respond_to do |format|
format.html # index.html.erb
format.json { render json: #community_topics }
end
end

Answer 1

I don't see your controller actions, and don't know names of variables, but anyway in case of nested routes you have to define all urls precisely with named routes, or with polymorphic helper (as i do).
So your form helper must be looking as next:
<%= form_for([#community, #community_topic], :html => { :class => 'form-horizontal' }) do |f| %>
it have to send request to /shop/walmart/topic/14/update (or 'new' if #community_topic is a new record)
community.rb:
you can just
def to_param
community_name
end
routes.rb:
resources :communities, :path => "shop", do
resources :community_topics, :path => "topic"#, :as => :'topic' *
end
# * named route 'community_topic' can conflict with 'community_topics' of standalone route for CommunityTopic. Let it be by default: 'community_community_topic'.