Question

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 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.

Answer 1

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