create_imports.rb

class CreateImports < ActiveRecord::Migration
  def self.up
    create_table :imports do |t|
      t.string :datatype
      t.integer :processed, :default => 0
      t.string :csv_file_name
      t.string :csv_content_type
      t.integer :csv_file_size
      t.timestamps
    end
  end

  def self.down
    drop_table :imports
  end
end

import.rb

class Import < ActiveRecord::Base
  has_attached_file :csv, 
                    :url => "#{RAILS_ROOT}/:basename.:extension",
                    :path => ":rails_root/:basename.:extension"
  validates_attachment_presence :csv
  
  validates_attachment_content_type :csv, :content_type => ['text/csv','text/comma-separated-values','text/csv','application/csv','application/excel','application/vnd.ms-excel','application/vnd.msexcel','text/anytext','text/plain']
end

imports_controller.rb

class ImportsController < ApplicationController
  
  def new
    @import = Import.new
  end

  def create
	  
    @import = Import.new(params[:import])

    respond_to do |format|
      if @import.save!
        self.import_inventory
        flash[:notice] = 'Inventory was successfully imported.'
        format.html { redirect_to('/products') }
      else
        flash[:error] = 'Inventory data import failed.'
        format.html { render :action => "new" }
      end
    end
  end

  def import_inventory
    @import = Import.last
    FasterCSV.foreach("#{@import.csv.path}") do |row|
      record = Product.new(
      :sku          => row[0],
      :category_id  => row[1],
      :name         => row[2],
      :price        => row[3],
      :created_at   => Time.now,
      :updated_at   => Time.now
      )
      record.save
    end
  end
  
end

upload.html.haml

- semantic_form_for Import.new, :html => { :multipart => true } do |f|
  - f.inputs do
    = f.input :csv, :as => :file, :hint => "Only TXT or CSV formats allowed.", :label => "Upload Inventory"
    = f.commit_button "Upload"