ruby-on-rails – Paperclip错误：缺少需要的模型attr_accessor

当我尝试上传图片给列表我得到这个错误：

Paperclip::Error in ListingsController#update
Listing model missing required attr_accessor for 'avatar_file_name'

listing_controller的第44行：

def update
 respond_to do |format|
  if @listing.update(listing_params)
    format.html { redirect_to @listing,notice: 'Listing was successfully updated.' }
    format.json { head :no_content }
  else

需要尝试的几件事情：即将一些代码添加到listing.rb模型中,以使可接受的图像为：头像更加健壮.这是几个stackoverflow帖子提到添加到listing.rb模型：

validates_attachment_content_type :avatar,:content_type => %w(image/jpeg image/jpg image/png)

不幸的是,当我附加图像时,我仍然会收到相同的错误.当我没有附加图像时,我的默认图像加载正常,并且列表正确创建.

我的房源编号：

class Listing < ActiveRecord::Base
  has_attached_file :avatar,:styles => { :medium => "150x",:thumb => "100x100>" },:default_url => "default.jpg"
  validates_attachment_content_type :avatar,:content_type => %w(image/jpeg image/jpg image/png) 
end

我的_form.html.erb部分：

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

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

  <div class="form-group">
    <%= f.label :name %><br>
    <%= f.text_field :name,class: "form-control" %>
  </div>
  <div class="form-group">
    <%= f.label :company %><br>
    <%= f.text_field :company,class: "form-control" %>
  </div>
  <div class="form-group">
    <%= f.label :email %><br>
    <%= f.text_field :email,class: "form-control" %>
  </div>
  <div class="form-group">
    <%= f.label :phone %><br>
    <%= f.text_field :phone,class: "form-control" %>
  </div>
  <div class="form-group">
    <%= f.label :avatar %><br>
    <%= f.file_field :avatar,class: "form-control" %>
  </div>
  <div class="form-group">
    <%= f.submit class: "btn btn-primary" %>
  </div>
<% end %>

我的listing_controller.rb控制器：

def update
    respond_to do |format|
      if @listing.update(listing_params)
        format.html { redirect_to @listing,notice: 'Listing was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @listing.errors,status: :unprocessable_entity }
      end
    end
  end
...
def listing_params
   params.require(:listing).permit(:name,:company,:email,:phone,:avatar)
end

和我的schema.rb文件

ActiveRecord::Schema.define(version: 20140329174335) do

  create_table "listings",force: true do |t|
    t.string   "name"
    t.string   "company"
    t.string   "email"
    t.string   "phone"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end

编辑：在运行$rails之后添加控制台输出生成纸夹列出头像

(我需要10个信誉点放在后,所以你必须解决链接http://i.imgur.com/c8KGTa3.png)