ruby-on-rails – Rails 4强参数和嵌套形式

我正在构建一个简单的应用程序( Ruby 2.0.0和Rails 4),用户可以在其中创建项目,并为每个项目创建多个屏幕.在创建屏幕时,用户可以上传屏幕截图,引用自己的模型(我这样做是为了处理同一屏幕的多个版本).

创建屏幕时,由于权限问题,似乎无法创建屏幕截图.这是服务器日志：

Processing by ScreensController#create as HTML
Parameters: {"utf8"=>"?","authenticity_token"=>"kezaGADsaLmY/+zozgbjEe5UfdeqRPg58FCf1qzfHxY=","screen"=>{"project_id"=>"24","name"=>"Billing","description"=>"This is the page where a user will enter their credit card information","screenshot"=>{"image"=>#  <ActionDispatch::Http::UploadedFile:0x007fcdce25b2c0 @tempfile=#<Tempfile:/var/folders/pv/srwrv0qj35b0hsxkt42l_z500000gn/T/RackMultipart20131007-91790-tewse9>,@original_filename="fb-banner.png",@content_type="image/png",@headers="Content-Disposition: form-data; name="screen[screenshot][image]"; filename="fb-banner.png"rnContent-Type: image/pngrn">}},"commit"=>"Create Screen"}
Unpermitted parameters: screenshot

这些是我的模特：

屏幕

class Screen < ActiveRecord::Base

  belongs_to :project
  has_many :screenshots

  validates :name,presence: true

  accepts_nested_attributes_for :screenshots

end

截图

class Screenshot < ActiveRecord::Base

  belongs_to :screen

end

这是我的screens_controller：

class ScreensController < ApplicationController
  before_action :set_screen,only: [:show,:edit,:update,:destroy]


  def index
    @screens = Screen.all
  end


  def show
  end


  def new
    @screen = Screen.new(:project_id => params[:project_id])
    @screen.screenshot.build
  end


  def edit
  end


  def create
    @screen = Screen.create(screen_params)
    if @screen.save
      flash[:notice] = "A new screen has been added to this project"
      redirect_to [@screen.project]
    else
      render :action => 'new'
    end
  end


  def update
    @screen = Screen.find(params[:id])
    if @screen.update_attributes(screen_params)
      flash[:notice] = "The screen has been successfully updated"
      redirect_to [@screen.project]
    else
      render :action => 'edit'
    end
  end

  def destroy
    @screen = Screen.find(params[:id])
    @screen.destroy
    flash[:notice] = "Successfully destroyed screen"
    redirect_to [@screen.project]
  end

  private
    def set_screen
      @screen = Screen.find(params[:id])
    end

    def screen_params
      params.require(:screen).permit(:project_id,:name,:description,screenshot_attributes: [ :id,:screen_id,:image,:version ])
    end
end

最后这是形式：

<%= form_for @screen,:html => { :multipart => true } do |f| %>
  <% if @screen.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@screen.errors.count,"error") %> prohibited this screen from being saved:</h2>

      <ul>
      <% @screen.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.hidden_field :project_id %>
  </div>
  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </div>
  <div class="field">
    <%= f.label :description %><br>
    <%= f.text_field :description %>
  </div>

  <%= f.fields_for :screenshot do |s| %>
    <%= s.hidden_field :screen_id,:value => @screen.id %>
    <%= s.hidden_field :version,:value => "1" %>
    <%= s.label :image %><br>
    <%= s.file_field :image %>
  <% end %>

  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

我希望这足以帮助我发现问题.在编程时我是新手,所以任何帮助都非常受欢迎.

<%= f.fields_for :screenshots do |s| %>

def screen_params
  params.require(:screen).permit(:project_id,screenshots_attributes: [ :id,:version ])
end

def new
  @screen = Screen.new(:project_id => params[:project_id])
  @screen.screenshots.build
end