title: Mongoid error "undefined method `delete' for :format:Symbol"
body: <p>I have 2 nested models: </p>
  
  <pre><code>class Interstate
    include Mongoid::Document
    field :name, :type =&gt; String
    field :url, :type =&gt; String
    field :time_zone, :type =&gt; String
    embeds_many :roadmaps
  end
  
  class Roadmap
    include Mongoid::Document
    field :title, :type =&gt; String
    field :privacy, :type =&gt; Integer
    field :interstate_id, :type =&gt; Integer
    embedded_in :interstate, :inverse_of =&gt; :roadmaps
  end
  </code></pre>
  
  <p>I'm not sure about the difference between <code>has_many|belongs_to</code> and <code>embeds_many|embedded_in</code>, but according to documentations last is better for me, anyway both doesn't work. Also I have nested resources:</p>
  
  <pre><code> resources :interstates do
     resources :roadmaps
   end
  </code></pre>
  
  <p>And Error appears when I'm trying to create Roadmap in Interstate.</p>
  
  <p>Roadmap controller is standard scaffold with before_filter method for Interstate defining:</p>
  
  <pre><code> private
   def get_interstate
     @interstate = Interstate.find(params[:interstate_id])
   end
  </code></pre>
  
  <p>In case with <code>embeds_many :roadmaps</code> and <code>embedded_in :interstate</code> other error occurs:</p>
  
  <pre><code>NoMethodError in Roadmaps#new
  
  Showing /home/alder/RubymineProjects/interstate/app/views/roadmaps/_form.html.haml where line #1 raised:
  
  undefined method `delete' for :format:Symbol
  
  Extracted source (around line #1):
  
  1: = simple_form_for(@interstate, @roadmap) do |f|
  2:   = f.error_notification
  3: 
  4:   .inputs
  
  Trace of template inclusion: app/views/roadmaps/new.html.haml
  
  Rails.root: /home/alder/RubymineProjects/interstate
  Application Trace | Framework Trace | Full Trace
  
  app/views/roadmaps/_form.html.haml:1:in `_app_views_roadmaps__form_html_haml___160176716082020505_38930380'
  app/views/roadmaps/new.html.haml:3:in `_app_views_roadmaps_new_html_haml__4577296702858298215_34853620'
  app/controllers/roadmaps_controller.rb:31:in `new'
  </code></pre>
  
  <p>Console:</p>
  
  <pre><code>undefined method `delete' for :format:Symbol (ActionView::Template::Error)
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/mongoid-2.3.2/lib/mongoid/persistence/operations.rb:80:in `notifying_parent?'                                                                                 
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/mongoid-2.3.2/lib/mongoid/persistence/operations/embedded/remove.rb:30:in `block in persist'                                                                  
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/mongoid-2.3.2/lib/mongoid/persistence/deletion.rb:23:in `prepare'                                                                                             
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/mongoid-2.3.2/lib/mongoid/persistence/operations/embedded/remove.rb:29:in `persist'                                                                           
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/mongoid-2.3.2/lib/mongoid/persistence.rb:56:in `remove'                                                                                                       
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/actionpack-3.1.1/lib/action_view/helpers/form_helper.rb:392:in `apply_form_for_options!'                                                                      
  /home/alder/.rvm/gems/ruby-1.9.2-p290@global/gems/actionpack-3.1.1/lib/action_view/helpers/form_helper.rb:365:in `form_for'
  </code></pre>
  
  <p><a href="http://www.sourcepod.com/fgfhrz41-5868" rel="nofollow">Full stack</a></p>
  
  <p>So, maybe I should add some options to cancel notifying, but more intresting why format is Symbol, I guess it should be Some Model Object. Perhaps <code>@interstate</code> is not the model.</p>
  
  <p>This code works with sqlite db correctly.</p>