how to read uploaded files

Question

I'm giving user opportunity to upload their files. However, application is not saving those files into the database, it only needs to get informations out of it.

So from a form which looks like this:

= simple_form_for @channel, method: :post do |f|
    = f.input :name
    = f.input :configuration_file, as: :file
    = f.submit

come params[:channel][:configuration_file]

#<ActionDispatch::Http::UploadedFile:0xc2af27c @original_filename="485.csv", @content_type="text/csv", @headers="Content-Disposition: form-data; name=\"channel[configuration_file]\"; filename=\"485.csv\"\r\nContent-Type: text/csv\r\n", @tempfile=#<File:/tmp/RackMultipart20140822-6972-19sqxq2>>

How exactly can i read from this thing? I tried simply

File.open(params[:channel][:configuration_file])

but it returns error

!! #<TypeError: can't convert ActionDispatch::Http::UploadedFile into String>

PS Additional solutions for xml and csv would be much appreciated!

score 3 · Accepted Answer · edited May 23 '17 at 10:33

According to the Rails docs:

http://api.rubyonrails.org/classes/ActionDispatch/Http/UploadedFile.html

an uploaded file supports the following instance methods, among others:

open() 

path()

read(length=nil, buffer=nil)

you could try:

my_data = params[:channel][:configuration_file].read

to get a string of the file contents?

or even:

my_data = File.read params[:channel][:configuration_file].path

Also, if the file can be long, you may want to open the file and read line by line. A few solutions here:

How to read lines of a file in Ruby

If you want to read a CSV file, you could try:

require 'csv'    

CSV.foreach(params[:channel][:configuration_file].path, :headers => true) do |row|
  row_hash = row.to_hash
  # Do something with the CSV data
end

Assuming you have headers in your CSV of course.

For XML I recommend the excellent Nokogiri gem:

http://nokogiri.org/

At least partly because it uses an efficient C library for navigating the XML. (This can be a problem if you're using JRuby). Its use is probably out of scope of this answer and adequately explained in the Nokogiri docs.

score 1 · Answer 2 · answered Aug 22 '14 at 09:42

From the documentation

The actual file is accessible via the tempfile accessor, though some of its interface is available directly for convenience.

You can change your code to:

file_content = params[:channel][:configuration_file].read

or if you want to use the File API:

file_content = File.read params[:channel][:configuration_file].path

how to read uploaded files

2 Answers2