How to parse the contents of a uploaded file in RoR - ruby-on-rails

Question

I am new to Rails.
In my project where users have to upload a file, I store it
then I have to parse the file contents and show it in new form.
I have successfully done the file uploading portion,
now how should I read the contents of it?

Answer 1

Try something like this:
upload = params[:your_upload_form_element]
content = upload.is_a?(StringIO) ? upload.read : File.read(upload.local_path)
Very small files can be passed as strings instead of uploaded files, therefore you should check for that and handle it accordingly.

Answer 2

You can open files and read their contents in Ruby using the File class, as this simple example demonstrates:
# Open a file in read-only mode and print each line to the console
file = File.open('afile.txt', 'r') do |f|
f.each do |line|
puts line
end
end

Answer 3

Complete Example
Take, for example, uploading an import file containing contacts. You don't need to store this import file, just process it and discard it.
Routes
routes.rb
resources :contacts do
collection do
get 'import/new', to: :new_import # import_new_contacts_path
post :import, on: :collection # import_contacts_path
end
end
Form
views/contacts/new_import.html.erb
<%= form_for #contacts, url: import_contacts_path, html: { multipart: true } do |f| %>
<%= f.file_field :import_file %>
<% end %>
Controller
controllers/contacts_controller.rb
def new_import
end
def import
begin
Contact.import( params[:contacts][:import_file] )
flash[:success] = "<strong>Contacts Imported!</strong>"
redirect_to contacts_path
rescue => exception
flash[:error] = "There was a problem importing that contacts file.<br>
<strong>#{exception.message}</strong><br>"
redirect_to import_new_contacts_path
end
end
Contact Model
models/contact.rb
def import import_file
File.foreach( import_file.path ).with_index do |line, index|
# Process each line.
# For any errors just raise an error with a message like this:
# raise "There is a duplicate in row #{index + 1}."
# And your controller will redirect the user and show a flash message.
end
end
Hope that helps others!
JP