ruby on rails 5 server-side CSV validation ERROR - ruby-on-rails

Question

In my lib/csv_validation.rb file I got my validate method:
def self.validate(file, delimiter, columns)
return false unless File.exist?(file)
content = File.read(file, encoding: 'utf-8')
return false unless content.valid_encoding?
content.each_line do |line|
return false if line.count(delimiter) < columns - 1
end
true
end
when I send a CSV file via ajax post request I get the following error:
Started POST "/students/import" for 127.0.0.1 at 2017-12-20 01:03:43 +0100
Processing by StudentsController#import as */*
Parameters: {"file"=>#<ActionDispatch::Http::UploadedFile:0x007fd0a228ca38 #tempfile=#<Tempfile:/tmp/RackMultipart20171220-4516-or6qi3.csv>, #original_filename="students_fail.csv", #content_type="text/csv", #headers="Content-Disposition: form-data; name=\"file\"; filename=\"students_fail.csv\"\r\nContent-Type: text/csv\r\n">}
Completed 500 Internal Server Error in 19ms (ActiveRecord: 0.0ms)
TypeError (can't convert ActionDispatch::Http::UploadedFile to IO (ActionDispatch::Http::UploadedFile#to_io gives Tempfile)):
app/models/student.rb:114:in `exist?'
app/models/student.rb:114:in `import'
app/controllers/students_controller.rb:50:in `import'
Rendering /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/diagnostics.text.erb
Rendering /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/_source.text.erb
Rendered /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/_source.text.erb (0.4ms)
Rendering /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/_trace.text.erb
Rendered /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/_trace.text.erb (0.4ms)
Rendering /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/_request_and_response.text.erb
Rendered /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/_request_and_response.text.erb (0.6ms)
Rendered /var/lib/gems/2.4.0/gems/actionpack-5.0.6/lib/action_dispatch/middleware/templates/rescues/diagnostics.text.erb (14.4ms)
DEPRECATION WARNING: Accessing mime types via constants is deprecated. Please change `Mime::HTML` to `Mime[:html]`. (called from acceptable_content_type? at /var/lib/gems/2.4.0/gems/web-console-2.3.0/lib/web_console/middleware.rb:58)
I was searching for can't convert ActionDispatch::Http::UploadedFile to IO but I just find something like can't convert ActionDispatch::Http::UploadedFile into String.
I am not sure how to handle this error or where I can find someone with the same problem.
sorry for my bad english and thx for help.

Answer 1

You'll want to use the ActionDispatch::Http::UploadedFile#tempfile method.
Documented here.
So you can call it like this:
File.read(file.tempfile, encoding: 'utf-8')
That will allow the object to transform to an actual file as opposed to an ActionDispatch object.
See this SO Article: Reading in file contents rails