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ActionDispatch::Flash

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] = "Post 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] = "Post successfully created"
    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 %>

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 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.

Constants

KEY

Public Class Methods

new(app) click to toggle source
# File lib/action_dispatch/middleware/flash.rb, line 234
def initialize(app)
  @app = app
end

Public Instance Methods

call(env) click to toggle source
# File lib/action_dispatch/middleware/flash.rb, line 238
def call(env)
  if (session = env['rack.session']) && (flash = session['flash'])
    flash.sweep
  end

  @app.call(env)
ensure
  session    = env['rack.session'] || {}
  flash_hash = env[KEY]

  if flash_hash
    if !flash_hash.empty? || session.key?('flash')
      session["flash"] = flash_hash
      new_hash = flash_hash.dup
    else
      new_hash = flash_hash
    end

    env[KEY] = new_hash
    new_hash.close!
  end

  if session.key?('flash') && session['flash'].empty?
    session.delete('flash')
  end
end

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