Ruby on rails 回形针不是'；t在继承的模型上存储文件

（我不熟悉回形针）

我有这个模型层次结构：

基本型号：

class QuestDescription < ActiveRecord::Base
end

图像描述控制器：

class ImageDescriptionsController < ApplicationController

  def new
    @imgD = ImageDescription.new
  end

  def create
    @imgD=ImageDescription.new(params[:imgD])
    if @imgD.save
      redirect_to :back, :flash => {:notice => "saved"} 
    else
      redirect_to :back, :flash => {:error => "error"} 
    end
  end

  def show
    @imgD=ImageDescription.find(params[:id])
  end
end    

---

您需要使用多部分HTML标记定义包含某些文件的帖子

<%= semantic_form_for @imgD, :html => { :multipart => true } do |form| %>
  <%= form.input :img%>
  <%= form.actions %>
<%end%>

{:multipart=>true}do| form |%>

真是愚蠢的错误：

@imgD=ImageDescription.new(params[:imgD])

没有任何意义。。。右行是

@imgD=ImageDescription.new(params[:image_description])

---

感谢您的回答，但没有任何更改：enctype=“multipart/form data”已经存在于表单的HTML中（我在rails 3.1中读到了一些自动逻辑的内容）

<%= image_tag @imgD.img.url %>

ImageDescription.create(:img => File.new(Rails.root + "public/images/grid.png"))
    (0.1ms) begin transaction
    SQL (31.9ms) INSERT INTO "quest_descriptions" ("created_at", "img_content_type", "img_file_name", "img_file_size", "img_updated_at", "type", "updated_at") VALUES (?, ?, ?, ?, ?, ?, ?) ["created_at", Wed, 15 Feb 2012 00:07:48 UTC +00:00], ["img_content_type", "image/png"], ["img_file_name", "grid.png"], ["img_file_size", 206], ["img_updated_at", Wed, 15 Feb 2012 00:07:48 UTC +00:00], ["type", "ImageDescription"], ["updated_at", Wed, 15 Feb 2012 00:07:48 UTC +00:00] commit transaction
    => #

<%= semantic_form_for @imgD, :html => { :multipart => true } do |form| %>
  <%= form.input :img%>
  <%= form.actions %>
<%end%>

@imgD=ImageDescription.new(params[:imgD])

@imgD=ImageDescription.new(params[:image_description])