You may want to consider reading the Rails Guide on nested resources:
http://guides.rubyonrails.org/routing.html#nested-resources
In a nutshell:
routes.rb
resources :galleries do
resources :pictures do
end
# Generates the routes: /galleries/:gallery_id/pictures
pictures_controller.rb
def new
@gallery = Gallery.find(params[:gallery_id])
@picture = Picture.new
end
def create
@gallery = Gallery.find(params[:gallery_id]) # gallery_id is passed in the URL
@picture = @gallery.build(params[:picture])
if @picture.save
# success
else
# fail
end
end
pictures/new.html.erb
<%= form_for [@gallery, @picture] do |f| %>
<div class="field">
<%= f.hidden_field :gallery_id , :value=>params[:gallery_id] %>
<%= f.label :image %><br />
<%= f.file_field :image %>
</div>
<div class="actions">
<%= f.submit "Create" %>
</div>
<% end %>
Ok, so the gallery_id is still passed through the URL, but I don’t really see anything wrong with that. You have to pass it somewhere, right? You really only have 3 sane choices on where to pass it: a hidden field, as a querystring parameter, or tucked away inside the URL (nested resource). Of the 3, the latter is IMHO the cleanest method.
If you want to make things even easier on yourself, I highly recommend looking into Jose Valim’s Inherited Resources gem that takes care of a lot of this boilerplate nastiness for you: