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 |
# File actionpack/lib/action_dispatch/middleware/flash.rb, line 259 def call(env) @app.call(env) ensure session = Request::Session.find(env) || {} flash_hash = env[KEY] if flash_hash && (flash_hash.present? || session.key?('flash')) session["flash"] = flash_hash.to_session_value env[KEY] = flash_hash.dup end if (!session.respond_to?(:loaded?) || session.loaded?) && # (reset_session uses {}, which doesn't implement #loaded?) session.key?('flash') && session['flash'].nil? session.delete('flash') end end