How can I get the full path of my selected file in Ruby on Rails?

I have put a file_field in my view :

<% form_for(:uploaded_file, @feed, :url => {:action=>'copy'}, :html=> {:multipart=>true}) do |f| %>
<%= f.file_field :uploaded_file %> <br>
<%= f.submit "Submit" %>
<% end %>

And I have a method in my controller that reads a Excel file:

def copy
    file = ""
    book = Spreadsheet.open 'excel_file'
    table = book.worksheet 'excel_sheet'
    table.each do |row|
      file << row
    end
end

Log with request

"authenticity_token"=>"BbQRomTLhiF2O54/G6eHwnnaWbLttUSvo31FO3ZtKoA=", 
"uploaded_file"=>{"uploaded_file"=>#<ActionDispatch::Http::UploadedFile:
 0x27b7ab‌​0 @original_filename="test.xlsx",@content_type="application
 /vnd.openxmlformats-offi开发者_StackOverflow社区cedocument.spreadsheetml.sheet", @headers=
 "Content-Disposition: form-data; name=\"uploaded_file[uploaded_file]\";
 filename=\"volumetrie.xlsx\"\r\nContent-Type: application/vnd.openxmlformats
 officedocument.spreadsheetml.sheet\r\n", @tempfile=#<File:C:/DOCUME~1/me/
 LOCALS~1/Temp/RackMultipart20110714-524-fy6vu>>}, "commit"=>"Submit"} 

I'm just trying to get the path of my selected file to insert it in my Spreadsheet.open method. The error message is : No such file or directory.

Instead of 'excel_file' that is the path of my Excel file, I would like to use the path of the file that I have choosed in the file_field in my view. How can I use this parameter ?

Thank you !

---

File.absolute_path(file)

Ruby Doc

---

You can't get path to file from form in modern browsers. You can work only with tempfile Should be available as params[ :uploaded_file ][ :tempfile ]

Edit try

file = Spreadshet::Excel.new('params[ :uploaded_file ][ :filename ]', 'w+')
file.write( params[ :uploaded_file ][ :tempfile ].read )