Question

I’d like to be able to read an XML file uploaded by the user (less than 100kb), but not have to first save that file to the database. I don’t need that file past the current action (its contents get parsed and added to the database; however, parsing the file is not the problem). Since local files can be read with:

File.read("export.opml")

I thought about just creating a file_field for :uploaded_file, then trying to read it with

File.read(params[:uploaded_file])

but all that does is throw a TypeError (can’t convert HashWithIndifferentAccess into String). I really have tried a lot of various things (including reading from the /tmp directory as well), but could get none of them to work.

I hope the brevity of my question doesn’t mask the effort I’ve given to try to solve this on my own, but I didn’t want to pollute this question with a hundred ways of how NOT to get it done. Big thanks to anyone who chimes in.

Here is my view:

<% form_for(:uploaded_file, @feed, :url => {:action=>'parse'}, :html=> {:multipart=>true}) do |f| %>  <p>
    <%= f.label :uploaded_file, 'Upload your file.' %><br />
    <%= f.file_field :uploaded_file %>
  </p>
  <p><%= f.submit 'upload' %></p>
<% end %>

I set up a custom action (upload) which handles the file_field upload, which after submission, is passed off to another custom action (parse) for processing. Could this be a part of my problem?

Answer 1

You are very close. Check the class type of params[:uploaded_file], it should typically be either a StringIO or a Tempfile object — both of which already act as files, and can be read using their respective read method(s).

Just to be sure (the class type of params[:uploaded_file] may vary depending on whether you are using Mongrel, Passenger, Webrick etc.) you can do a slightly more exhaustive attempt:

# Note: use form validation to ensure that
#  params[:uploaded_file] is not null

file_data = params[:uploaded_file]
if file_data.respond_to?(:read)
  xml_contents = file_data.read
elsif file_data.respond_to?(:path)
  xml_contents = File.read(file_data.path)
else
  logger.error "Bad file_data: #{file_data.class.name}: #{file_data.inspect}"
end

If, in your case, it turns out that params[:uploaded_file] is a hash, make sure that you have not mistakingly flipped the object_name and method parameters when invoking file_field in your view, or that your server is not giving you a hash with keys like :content_type etc. (in which case please comment on this post with the Bad file_data ... output from development.log/production.log.)