권한 부여 중첩 및 다형성 자원 (캉캉)

있는 모델 사용자, 프로젝트, 문서, 이슈, 코멘트, 능력 :권한 부여 중첩 및 다형성 자원 (캉캉)

class User < ActiveRecord::Base 
    has_and_belongs_to_many :projects 
end 

class Project < ActiveRecord::Base 
    has_and_belongs_to_many :users 
    has_many :documents 
end 

class Issues < ActiveRecord::Base 
    belongs_to :project 
    has_many :comments, :as => :commentable 
end 

class Document < ActiveRecord::Base 
    belongs_to :project 
    has_many :comments, :as => :commentable 
end 

class Comment < ActiveRecord::Base 
    belongs_to :commentable, :polymorphic => true 
end 

class Ability 
    include CanCan::Ability 

    def initialize(user) 
    user ||= User.current 

    can :read, Project, :id => user.project_ids 
    can :manage, Document, :project => { :id => user.project_ids } 
    end 
end

경로 :

resources :projects, :shallow => true, :path => '/', :only => :show do 
    resources :documents do 
    resources :comments 
    end 
    resources :issues do 
    resources :comments 
    end 
end

컨트롤러 :

class DocumentsController < InheritedResources::Base 
    load_and_authorize_resource :project 
    load_and_authorize_resource :document, :through => :project, :shallow => true 

    # GET /1/documents 
    # GET /1/documents.json 
    def index 
    @project = Project.find(params[:project_id]) 
    @documents = @project.documents.page(params[:page]) 

    respond_to do |format| 
     format.html 
     format.json { render :json => @documents } 
    end 
    end 

    # POST /1/documents/new 
    # POST /1/documents/new.json 
    def new 
    @project = Project.find(params[:project_id]) 
    @document = @project.documents.build 

    respond_to do |format| 
     format.html 
     format.json { render :json => @document } 
    end 
    end 

    # POST /1/documents 
    # POST /1/documents.json 
    def create 
    @project = Project.find(params[:project_id]) 
    @document = @project.documents.build(params[:document]) 

    respond_to do |format| 
     if @document.save 
     format.html { redirect_to @document, notice: 'Document was successfully created.' } 
     format.json { render json: @document, status: :created, location: @document } 
     else 
     format.html { render action: "new" } 
     format.json { render json: @document.errors, status: :unprocessable_entity } 
     end 
    end 
    end 
end

프로젝트에 대한 능력은 괜찮지 만 문서 작성에 실패합니다. 질문 :