Trouble with uploading file after upgrating rails from 3.2 to 4

问题

Uploading files in my gallery worked fine with Rails 3, but after upgrate I get exeption wrong argument type ActionDispatch::Http::UploadedFile (expected String) in this line @reel.update_attributes(reels_params). I don't use any gem for handle file uploading, because I need specific processing and store my files in db. After upgraded to rails 4, I added only 1 method to working with strong params in controller reels_params.

Controller:

class Admin::ReelsController < AdminController
  before_action :set_reel, only: [:show, :edit, :update, :destroy]
  def update
    respond_to do |format|
      if @reel.update_attributes(reels_params)
        format.html { redirect_to admin_reel_path(@reel), notice: t('helpers.messages.update_success') }
      else
        format.html { render action: "edit" }
      end
    end
  end
  ...
  private
    def set_reel
      @reel = Reel.find(params[:id])
    end
    def reels_params
      params.require(:reel).permit!
    end
end

View:

= form_for [:admin, @reel], :html => { :class => 'form-horizontal form-admin', :multipart => true } do |f|
  .form-group
    = f.label 'Gallery', :class => 'control-label col-sm-2'
    .col-sm-10
      - item.images.each do |img|
        = f.fields_for :images, img do |img_f|
          = img_f.text_field :title
          = img_f.file_field :data, class: 'img_upload'

How to correct my code?

回答1:

To break down this problem, I took the view down to only the single image-element

<%= form_tag({action: :update}, multipart: true,  method: "patch") do %>
    <%= file_field_tag 'image' %>

    <div class="actions">
      <%= submit_tag %>
    </div>

<% end %>

with controller:

def update
  @user.image = params[:image]  <<------Fails on this line
  respond_to do |format|
  if @user.save ....

The Error is: "wrong argument type ActionDispatch::Http::UploadedFile (expected String)"

Looking here: http://api.rubyonrails.org/classes/ActionDispatch/Http/UploadedFile.html ... we find the ".read" option, so I modified the controller to read:

def update
  @user.image = params[:image].read  <<------added the suffix here
  respond_to do |format|
  if @user.save ... 

It works, and I can read the image back from the file OK. So, it appears we will need to isolate and save blobs separately, adding the ".read" suffix, and cannot save it in a group with other params until this BUG/(feature) is fixed.

来源：https://stackoverflow.com/questions/20603765/trouble-with-uploading-file-after-upgrating-rails-from-3-2-to-4