Rails 4: First argument in form cannot contain nil or be empty -

in our rails 4 app, there 4 models:

class user < activerecord::base   has_many :administrations, dependent: :destroy   has_many :calendars, through: :administrations end  class administration < activerecord::base   belongs_to :user   belongs_to :calendar end  class calendar < activerecord::base   has_many :administrations, dependent: :destroy   has_many :users, through: :administrations end  class post < activerecord::base     belongs_to :calendar end 

we have routed corresponding resources routing concerns, follows:

concern :administratable   resources :administrations end  resources :users, concerns: :administratable resources :calendars, concerns: :administratable 

to create new @calendar, use following form:

<h2>create new calendar</h2> <%= form_for(@calendar) |f| %>   <%= render 'shared/error_messages', object: f.object %>   <div class="field">     <%= f.text_field :name, placeholder: "your new calendar name" %>   </div>   <%= f.submit "create", class: "btn btn-primary" %> <% end %> 

when embed form user's show.html.erb (so user can create new calendar profile), works fine.

however, have special page, call dashboard, user see calendars , create new one.

we believe logical url should /users/:id/administrations.

so, embedded above form in administration's index.html.erb.

and , visit instance /users/1/administrations, following error:

argumenterror in administrationscontroller#index  first argument in form cannot contain nil or empty  extracted source (around line #432):  else   object      = record.is_a?(array) ? record.last : record   raise argumenterror, "first argument in form cannot contain nil or empty" unless object   object_name = options[:as] || model_name_from_record_or_class(object).param_key   apply_form_for_options!(record, object, options) end 

edit: here our administrations#controller:

class administrationscontroller < applicationcontroller    def to_s     role   end    def index     @user = current_user     @administrations = @user.administrations   end    def show     @administration = administration.find(params[:id])   end  end 

any idea of doing wrong?

first argument in form cannot contain nil or empty

the reason @calendar not initialised in controller action, @calendar nil. error.

to your form work in administrations/index.html.erb, should having below code in index action of administrations_controller.

def index   @user = current_user   @administrations = @user.administrations   @calendar = calendar.new # one. end