redirect_to使った時にBootstrap対応のフラッシュメッセージを表示させる ref: http://qiita.com/Yama-to/items/4d19a714d8bf5bfbabdd

application.html.haml

  %body
    = render "layouts/header"
    - flash.each do |key, value|
      - key = "info" if key == "notice"
      - key = "danger"  if key == "alert"
      = content_tag :div, value, class: "alert alert-#{key}"
    = yield
    = render "layouts/footer"

application_controller.rb

class ApplicationController < ActionController::Base
  add_flash_types :success, :info, :warning, :danger
end

flash_samples_controller.rb

def create
  review = current_user.reviews.new(review_params)
  if review.save
    redirect_to books_url, success: "Successfully created your prototype."
  else
    redirect_to root_url,  warning: "Unfortunately failed to create."
  end
end