Terminal Commands:

rails g model Product name:string quantity:integer price:decimal{12,2}
rake db:migrate

Lates create controller.

Terminal Commands:

rails g controller Products

Controller Code:

class HistoriesController < ApplicationController
    def create
        file = Dir.glob("#{Rails.root}/public/products/**/*.csv") #=> This folder directory where read the CSV files
        file.each do |file|
            Product.import(file)
        end
    end
end 

Model:

class Product< ApplicationRecord
  def self.import(file)
      CSV.foreach(file.path, headers: true) do |row|
          Product.create! row.to_hash
      end
  end
end

routes.rb

resources :products

app/config/application.rb

require 'csv'

Now open your development console & run

=> ProductsController.new.create #=> Uploads your whole CSV files from your folder directory