The flash provides a way to pass temporary objects 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] = "Successfully created" before redirecting to a display action that can then expose the flash to its template. Actually, that exposure is automatically done. Example:
class PostsController < ActionController::Base def create # save post flash[:notice] = "Successfully created post" redirect_to posts_path(@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 %>
This example just places a string in the flash, but you can put any object in there. And of course, you can put as many as you like at a time too. 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.
# File actionpack/lib/action_controller/flash.rb, line 29 29: def self.included(base) 30: base.class_eval do 31: include InstanceMethods 32: 33: alias_method_chain :perform_action, :flash 34: alias_method_chain :reset_session, :flash 35: alias_method_chain :redirect_to, :flash 36: 37: helper_method :alert 38: helper_method :notice 39: end 40: end