I came across file uploading problem in Rails. I found `file_field :file` helper, that can be used with `form_for(@some_model)`. However, I cannot find any usage for this case, as those tags are used to create/edit some model, by mass assigning. There is, AFAIK, no possibility to treat fileupload as typical field ( See [File upload won't work in Ruby on Rails 3 using Multipart Form](https://stackoverflow.com/questions/12678962/file-upload-wont-work-in-ruby-on-rails-3-using-multipart-form) ). In such a case, manual operation on uploaded file is required. So, why would someone even want to puts a fileupload as a part of model editing? 

photo.rb

```
   class Photo < ActiveRecord::Base
       attr_accessible :name, :filename,
   end

```

photo\_form.html.erb

```
<%= form_for(@photo, :multipart => true) do |f| %>

  <%= f.label :name %> 
  <%= f.text_field :name %>

  <%= f.file_field :file %>

  <%= f.submit %>

<% end %>

```

photos\_controller.rb

```
def create
    @photo = Photo.new(params[:photo])

```

line above fails, because theres no :file attribute. It must be handled before and manually removed from `:params`. Once more - is there any real usage for such tags?