Estou tentando seguir este tutorial do coderwall sobreCriando um sistema de convite com escopo para Rails.

No meu aplicativo Rails 4, tenho os seguintes modelos:

class User < ActiveRecord::Base
  has_many :administrations
  has_many :calendars, through: :administrations
  has_many :invitations, :class_name => "Invite", :foreign_key => 'recipient_id'
  has_many :sent_invites, :class_name => "Invite", :foreign_key => 'sender_id'
end

class Calendar < ActiveRecord::Base
  has_many :administrations
  has_many :users, through: :administrations
  has_many :invites
end

class Administration < ActiveRecord::Base
  belongs_to :user
  belongs_to :calendar
end

class Invite < ActiveRecord::Base
  belongs_to :calendar
  belongs_to :sender, :class_name => 'User'
  belongs_to :recipient, :class_name => 'User'
end

Aqui está a correspondência entre meus modelos e os modelos do tutorial:

User <=>UserCalendar <=>UserGroupAdministration <=>MembershipInvite <=>Invite

Agora estou noFazendo um novo convite seção:

oInvite modelo foi atualizado com obefore_create filtro egenerate_token método.oInvites controlador foi atualizado com ocreate açao.

No entanto, quando visito a visualização de edição do calendário para preencher o formulário de convite, recebo o seguinte erro:

NoMethodError in CalendarsController#edit
undefined method `relation_delegate_class' for Invite:Class
def edit
  @user = current_user
  @invite = @calendar.invites.build
  authorize @calendar
end

A questão parece vir do@invite = @calendar.invites.build linha.

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ATUALIZAR: aqui está o conteúdo do meu modelo de convite:

class Invite < ActiveRecord::Base
  belongs_to :calendar
  belongs_to :sender, :class_name => 'User'
  belongs_to :recipient, :class_name => 'User'

  before_create :generate_token

  def generate_token
   self.token = Digest::SHA1.hexdigest([self.calendar_id, self.recipient_role, Time.now, rand].join)
  end

end

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ATUALIZAÇÃO 2: noessa questão, o autor explica que o problema pode vir do CanCanCan & Rolify. Eu não uso essas jóias, mas eu uso o Pundit. Achei que isso seria útil no contexto da minha pergunta.

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ATUALIZAÇÃO 3: aqui também está a migração que usei para oInvite modelo:

class CreateInvites < ActiveRecord::Migration
  def change
    create_table :invites do |t|
      t.string :email 
      t.integer :calendar_id
      t.integer :sender_id
      t.integer :recipient_id
      t.string :recipient_role
      t.string :token
      t.timestamps null: false
    end
  end
end

Gostaria de saber se o problema pode ser causado pelot.string :recipient_role, desde orole de um dadouser só existe noadministration mesa, para um dadocalendar: E se:recipient_role é automaticamente interpretado comorecipient.role pelo Rails, então talvez isso esteja causando o erro?

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ATUALIZAÇÃO 4: aqui está o conteúdo do CalendarsController:

class CalendarsController < ApplicationController
  before_action :set_calendar, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!

  # GET /calendars
  # GET /calendars.json
  def index
    @user = current_user
    @calendars = @user.calendars.all
  end

  # GET /calendars/1
  # GET /calendars/1.json
  def show
    @user = current_user
    @calendar = @user.calendars.find(params[:id])
    authorize @calendar
  end

  # GET /calendars/new
  def new
    @user = current_user
    @calendar = @user.calendars.new
    authorize @calendar
  end

  # GET /calendars/1/edit
  def edit
    @user = current_user
    @invite = @calendar.invites.build
    authorize @calendar
  end

  # POST /calendars
  # POST /calendars.json
def create
  @user = current_user
  @calendar = @user.calendars.create(calendar_params)
  authorize @calendar
  respond_to do |format|
    if @calendar.save
      current_user.set_default_role(@calendar.id, 'Owner')
      format.html { redirect_to calendar_path(@calendar), notice: 'Calendar was successfully created.' }
      format.json { render :show, status: :created, location: @calendar }
    else
      format.html { render :new }
      format.json { render json: @calendar.errors, status: :unprocessable_entity }
    end
  end
end

  # PATCH/PUT /calendars/1
  # PATCH/PUT /calendars/1.json
  def update
    @user = current_user
    @calendar = Calendar.find(params[:id])
    authorize @calendar
    respond_to do |format|
      if @calendar.update(calendar_params)
        format.html { redirect_to calendar_path(@calendar), notice: 'Calendar was successfully updated.' }
        format.json { render :show, status: :ok, location: @calendar }
      else
        format.html { render :edit }
        format.json { render json: @calendar.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /calendars/1
  # DELETE /calendars/1.json
  def destroy
    @user = current_user
    @calendar.destroy
    authorize @calendar
    respond_to do |format|
      format.html { redirect_to calendars_url, notice: 'Calendar was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_calendar
      @calendar = Calendar.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def calendar_params
      params.require(:calendar).permit(:name)
    end
end

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ATUALIZAÇÃO 5: aqui estão os logs do servidor:

Started GET "/calendars/2/edit" for ::1 at 2015-09-14 11:44:13 -0700
Processing by CalendarsController#edit as HTML
  Parameters: {"id"=>"2"}
  Calendar Load (0.1ms)  SELECT  "calendars".* FROM "calendars" WHERE "calendars"."id" = ? LIMIT 1  [["id", 2]]
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ?  ORDER BY "users"."id" ASC LIMIT 1  [["id", 1]]
Completed 500 Internal Server Error in 3ms (ActiveRecord: 0.3ms)

NoMethodError (undefined method `relation_delegate_class' for Invite:Class):
  app/controllers/calendars_controller.rb:30:in `edit'


  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/_source.erb (6.0ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (2.8ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (1.7ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1@global/gems/actionpack-4.2.2/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout (68.9ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_markup.html.erb (0.5ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_inner_console_markup.html.erb within layouts/inlined_string (0.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_prompt_box_markup.html.erb within layouts/inlined_string (0.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/style.css.erb within layouts/inlined_string (0.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/console.js.erb within layouts/javascript (39.3ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/main.js.erb within layouts/javascript (0.4ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/error_page.js.erb within layouts/javascript (0.4ms)
  Rendered /Users/TXC/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/index.html.erb (94.2ms)

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ATUALIZAÇÃO 6: Acabei de perceber que não tinha

def invite_params
  params.require(:invite)
end

noInvites controlador: isso poderia ser a raiz do problema aqui?

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Alguma idéia sobre o significado dessa mensagem de erro e como corrigir o problema?