csv uploader throwing nil or empty error - ruby-on-rails

Question

I have a site that has an a table called orders, the order model, and a csv_files_controller (separate from the orders controller).
in the model I have the following:
def self.import(csv_file)
CSV.foreach(csv_file.path, headers: true) do |row|
Order.create! row.to_hash
end
end
in the csv_files_controller I have the following:
class CsvFilesController < ApplicationController
def new
#csv_file = CsvFile.new
end
def create
#csv_file = CsvFile.new(params[:csv_file])
if #csv_file.save
Order.import
redirect_to csv_file, notice: "Orders uploaded successfully"
end
end
def show
#csv_file = CsvFile.find(params[:id])
respond_to do |format|
format.html # show.html.erb
format.json { render json: #csv_file }
end
end
end
my upload_form partial being rendered by a page in the orders views from csv_files views:
<%= form_for #csv_file do |f| %>
<div class="controls">
<%= f.file_field :csv_file, accept: 'csv', :class => 'btn btn-xs btn-info' %>
<%= f.submit "Upload Orders", :class => 'btn btn-xs btn-success' %>
</div>
<% end %>
my routes.rb also has
resources :csv_files
when I try to load the page for the uploading I am getting a First argument in form cannot contain nil or be empty error. I am not sure what I have done wrong for it to say that.
Now if I change the form_for to :csv_files the page will load, but it is blank; no browse for file or submit button appear, but the error goes away. Doesn't matter though if the form isn't working. I am using rails 4 so I shouldn't need he :html => {multipart: true} and even when it was there it didn't change anything.
I can't figure out why it is throwing the error.
Update 9-1-15:
I have made a ton of changes, but now I get
No route matches [POST] "/orders/upload_page"
but my rake routes shows I have set my post route to :import.
resources :orders do
collection do
post :import
get :upload_page, as: 'upload_page'
get :search, as: 'search'
get :csv_report, as: 'csv_report'
get :overdue_csv_report, as: 'overdue_csv_report'
end
end
I don't understand why it is routing post to the upload_page.

Answer 1

The answer was threfold:
I got rid of the csv_files controller, etc. and moved all the code to the original orders controller.
I was trying to use a form_for .... do |f| and I had to revert to form_tag .... do for the form and spell everything out to get the post to work.
code snips:
Model:
def self.import(csv_file)
CSV.foreach(csv_file, headers: true) do |row|
Order.create! row.to_hash
end
end
Controller:
def import
Order.import(params[:csv_file].tempfile)
redirect_to orders_path, notice: "Orders imported"
end
form partial:
<%= form_tag import_orders_path, multipart: true do %>
<div class="controls">
<%= file_field_tag :csv_file, accept: 'csv', :class => 'btn btn-xs btn-info' %>
<%= submit_tag "Upload Orders", :class => 'btn btn-xs btn-success' %>
</div>
<% end %>
Routes:
resources :orders do
collection do
post :import
I am now working on ensuring that the uploads are using the validations in the model as it seems to be skipping it.