Paperclip wrong attachment url on validation errors

I have a preview of attached image in my update form. The problem appears when user gets validation errors on attachment field. In this case image thumbnail url becomes as if 开发者_开发技巧an image was uploaded without any errors (it shows name of file that was not saved at server).

Here is how I get image url in my view: <%= image_tag(@product.photo.url(:medium)) %>.

Controller:

def update
  @product = Product.find(params[:id])
  @product.update_attributes(params[:product]) ? redirect_to('/admin') : render(:new)
end

def edit
  @product = Product.find(params[:id])
  render :new
end

Model:

class Product < ActiveRecord::Base

  <...>

  @@image_sizes = {:big => '500x500>', :medium => '200x200>', :thumb=> '100x100>'}

  has_attached_file :photo, :styles => @@image_sizes, :whiny => false
  validates_attachment_presence :photo
  validates_attachment_content_type :photo, :content_type => ['image/jpeg', 'image/jpg', 'image/png', 'image/gif'], :message => I18n.t(:invalid_image_type)
  validates_attachment_size :photo, :less_than => 1.megabytes, :message => I18n.t(:invalid_image_size, :max => '1 Mb')
  after_post_process :save_image_dimensions

  <...>

end

UPD: The simpliest solution is to add @photo_file_url = @product.photo.url(:medium) in controller's update action before @product.update_attributes and <% @photo_file_url ||= @product.photo.url(:medium) %> in the view.

---

I actually had the same issue and here is what I had done (which seems a bit of a hack) but works and will show the default or previous image on update failure

after_validation :logo_reverted?

def logo_reverted?
  unless self.errors[:logo_file_size].blank? or self.errors[:logo_content_type].blank?
    self.logo.instance_write(:file_name, self.logo_file_name_was) 
    self.logo.instance_write(:file_size, self.logo_file_size_was) 
    self.logo.instance_write(:content_type, self.logo_content_type_was)
  end
end

---

In my app I had similar issues, so I used:

<%= image_tag(@product.photo.url(:medium)) if @photo.valid? %>

That way nothing shows up if the Photo isn't valid (ie successfully created), but when you edit existing records the image is shown.

Hope that helps.