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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.

Public Class Methods

new(app) click to toggle source
     # File lib/action_dispatch/middleware/flash.rb, line 173
173:     def initialize(app)
174:       @app = app
175:     end

Public Instance Methods

call(env) click to toggle source
     # File lib/action_dispatch/middleware/flash.rb, line 177
177:     def call(env)
178:       if (session = env['rack.session']) && (flash = session['flash'])
179:         flash.sweep
180:       end
181: 
182:       @app.call(env)
183:     ensure
184:       session    = env['rack.session'] || {}
185:       flash_hash = env['action_dispatch.request.flash_hash']
186: 
187:       if flash_hash && (!flash_hash.empty? || session.key?('flash'))
188:         session["flash"] = flash_hash
189:       end
190: 
191:       if session.key?('flash') && session['flash'].empty?
192:         session.delete('flash')
193:       end
194:     end

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