Criando uma action para importação de arquivos CSV

_form_import.html.slim

= simple_form_for @mailing, :url => import_mailings_path, multipart: true do |f|
  = f.error_notification

  .form-inputs
    = f.input :file, as: :file

  .form-actions
    = f.button :submit, "Enviar Arquivo", class: 'btn btn-primary'

index.html.slim

h1 Listar Contatos

hr

table.table.table-striped
  thead
    tr
      th Email
      th Empresa
      th
      

  tbody
    - @mailings.each do |mailing|
      tr
        td = mailing.email
        td = mailing.company
        td
          .btn-group.pull-right
            = link_to 'Ver', mailing, class: 'btn btn-default btn-sm'
            = link_to 'Editar', edit_mailing_path(mailing), class: 'btn btn-default btn-sm'
            = link_to 'Excluir', mailing, data: {:confirm => 'Tem certeza?'}, :method => :delete, class: 'btn btn-default btn-sm'

= link_to 'Novo Contato', new_mailing_path, class: 'btn btn-primary'

hr

h4 Importar Lista

== render 'form_import'

mailing.rb

class Mailing < ActiveRecord::Base
  	
	belongs_to :company
	has_one :profile

	attr_accessor :file

	validates :email, presence: true
	validates :email, uniqueness: true

	def self.import(file)
		CSV.foreach('file', headers: true) do |row|
	    	Mailing.create! row.to_hash
	  	end
	end
  	
end

mailings_controller.rb

class MailingsController < ApplicationController
  before_action :set_mailing, only: [:show, :edit, :update, :destroy]

  # GET /mailings
  def index
    @mailings = Mailing.all
    @mailing = Mailing.new
  end

  # GET /mailings/1
  def show
  end

  # GET /mailings/new
  def new
    @mailing = Mailing.new
  end

  # GET /mailings/1/edit
  def edit
  end

  # POST /mailings
  def create
    @mailing = Mailing.new(mailing_params)

    if @mailing.save
      redirect_to mailings_path, notice: 'Mailing was successfully created.'
    else
      render :new
    end
  end

  # PATCH/PUT /mailings/1
  def update
    if @mailing.update(mailing_params)
      redirect_to @mailing, notice: 'Mailing was successfully updated.'
    else
      render :edit
    end
  end

  # DELETE /mailings/1
  def destroy
    @mailing.destroy
    redirect_to mailings_url, notice: 'Mailing was successfully destroyed.'
  end

  def import
    Mailing.import(params[:file])
    redirect_to mailings_path, notice: "Contatos importados."
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_mailing
      @mailing = Mailing.find(params[:id])
    end

    # Only allow a trusted parameter "white list" through.
    def mailing_params
      params.require(:mailing).permit(:email, :company_id)
    end

end

routes.rb

Rails.application.routes.draw do
  
  resources :mailings do
    collection { post :import }
  end
  
  resources :profiles 
  resources :companies

  root 'companies#index'
end