gistfile1.rb

-----------------models/*--------------------
class Alpha < ActiveRecord::Base
  has_many :bravos, :dependent => :destroy
  has_many :charlies, :through => :bravos
end

class Bravo < ActiveRecord::Base
  belongs_to :alpha
  has_and_belongs_to_many :charlies
end

class Charlie < ActiveRecord::Base
  has_and_belongs_to_many :bravos
  has_one :delta
end

class Delta < ActiveRecord::Base
  belongs_to :charlie
end

---------------------------routes.rb---------------------------

resources :alphas do
  resources :bravos
  resources :charlies
end

resources :charlies do
  resources :delta
end

-----------------views/alpha/show.html.erb---------------------

<%= render @alpha.charlies %>

-----------------views/charlie/_charlie.html.erb---------------

<%# charlie fields %>
<%= render :partial => "deltas/form", :locals => { :charlie => charlie } %>

-----------------views/charlie/_form.html.erb------------------

<%= form_for [charlie, charlie.build_delta], url: charlie_delta_path(charlie) do |f| %>
  <%# form stuff %>
<% end %>

--------------------------ERRORS-------------------------------

No route matches {:action=>"show", :controller=>"delta", :alpha_id=>"1", :id=>nil, :charlie_id=>#<Audit id: 2, ...>, :format=>nil} missing required keys: [:id]

--------------------------rake routes--------------------------

                Prefix Verb   URI Pattern                                         Controller#Action
            home_index GET    /home/index(.:format)                               home#index
          alpha_bravos GET    /alphas/:alpha_id/bravos(.:format)             bravos#index
                       POST   /alphas/:alpha_id/bravos(.:format)             bravos#create
       new_alpha_bravo GET    /alphas/:alpha_id/bravos/new(.:format)         bravos#new
      edit_alpha_bravo GET    /alphas/:alpha_id/bravos/:id/edit(.:format)    bravos#edit
           alpha_bravo GET    /alphas/:alpha_id/bravos/:id(.:format)         bravos#show
                       PATCH  /alphas/:alpha_id/bravos/:id(.:format)         bravos#update
                       PUT    /alphas/:alpha_id/bravos/:id(.:format)         bravos#update
                       DELETE /alphas/:alpha_id/bravos/:id(.:format)         bravos#destroy
        alpha_charlies GET    /alphas/:alpha_id/charlies(.:format)            charlies#index
                       POST   /alphas/:alpha_id/charlies(.:format)            charlies#create
     new_alpha_charlie GET    /alphas/:alpha_id/charlies/new(.:format)        charlies#new
    edit_alpha_charlie GET    /alphas/:alpha_id/charlies/:id/edit(.:format)   charlies#edit
         alpha_charlie GET    /alphas/:alpha_id/charlies/:id(.:format)        charlies#show
                       PATCH  /alphas/:alpha_id/charlies/:id(.:format)        charlies#update
                       PUT    /alphas/:alpha_id/charlies/:id(.:format)        charlies#update
                       DELETE /alphas/:alpha_id/charlies/:id(.:format)        charlies#destroy
                alphas GET    /alphas(.:format)                                alphas#index
                       POST   /alphas(.:format)                                alphas#create
             new_alpha GET    /alphas/new(.:format)                            alphas#new
            edit_alpha GET    /alphas/:id/edit(.:format)                       alphas#edit
                 alpha GET    /alphas/:id(.:format)                            alphas#show
                       PATCH  /alphas/:id(.:format)                            alphas#update
                       PUT    /alphas/:id(.:format)                            alphas#update
                       DELETE /alphas/:id(.:format)                            alphas#destroy
   charlie_delta_index GET    /charlies/:charlie_id/delta(.:format)              delta#index
                       POST   /charlies/:charlie_id/delta(.:format)              delta#create
     new_charlie_delta GET    /charlies/:charlie_id/delta/new(.:format)          delta#new
    edit_charlie_delta GET    /charlies/:charlie_id/delta/:id/edit(.:format)     delta#edit
         charlie_delta GET    /charlies/:charlie_id/delta/:id(.:format)          delta#show
                       PATCH  /charlies/:charlie_id/delta/:id(.:format)          delta#update
                       PUT    /charlies/:charlie_id/delta/:id(.:format)          delta#update
                       DELETE /charlies/:charlie_id/delta/:id(.:format)          delta#destroy
              charlies GET    /charlies(.:format)                                   charlies#index
                       POST   /charlies(.:format)                                   charlies#create
           new_charlie GET    /charlies/new(.:format)                               charlies#new
          edit_charlie GET    /charlies/:id/edit(.:format)                          charlies#edit
               charlie GET    /charlies/:id(.:format)                               charlies#show
                       PATCH  /charlies/:id(.:format)                               charlies#update
                       PUT    /charlies/:id(.:format)                               charlies#update
                       DELETE /charlies/:id(.:format)                               charlies#destroy
                import POST   /home/import(.:format)                              home#import
                  type GET    /alphas/:alpha_id/type/:type_charlies(.:format) alphas#type
                  root GET    /                                                   home#index