The flash provides a way to pass temporary primitive-types (String, Array, Hash) between actions. Anything you place in the flash will be exposed to the very next action and then cleared out. This is a great way of doing notices and alerts, such as a create action that sets flash[:notice] = "Post successfully created" before redirecting to a display action that can then expose the flash to its template. Actually, that exposure is automatically done.
class PostsController < ActionController::Base def create # save post flash[:notice] = "Post successfully created" redirect_to @post end def show # doesn't need to assign the flash notice to the template, that's done automatically end end show.html.erb <% if flash[:notice] %> <div class="notice"><%= flash[:notice] %></div> <% end %>
Since the notice and alert keys are a common idiom, convenience accessors are available:
flash.alert = "You must be logged in" flash.notice = "Post successfully created"
This example places a string in the flash. And of course, you can put as many as you like at a time too. If you want to pass non-primitive types, you will have to handle that in your application. Example: To show messages with links, you will have to use sanitize helper.
Just remember: They’ll be gone by the time the next action has been performed.
See docs on the FlashHash class for more details about the flash.
KEY = 'action_dispatch.request.flash_hash'.freeze