Flash and the Rails Action Controller

Problem

You’ve created a flash message and are displaying it to the user. You’d like to extend the life of that message for one more request than would normally exist.

Solution

You can call the keep method of the Flash class on a specific entry, or the entire contents of the flash hash. This technique is useful for redisplaying flash messages in subsequent requests without explicitly recreating them.

To demonstrate this, create the following RentalController:

app/controllers/rental_controller.rb:

  class RentalController
< ApplicationController

    def step_one
      flash.now[:reminder] = 'There is a $20 fee for late
payments.'
      flash.keep(:reminder)
    end
    def step_two
    end

    def step_three
    end
  end 

And create the following three views:

app/views/rental/step_one.rhtml:

  <h1>Step one!</h1>
  <% if flash[:reminder] %>
    <p style="color: green;"><%= flash[:reminder] %></p>
  <% end %>
  <a href="step_two">step_two</a>

app/views/rental/step_two.rhtml:

  <h1>Step two!</h1>
  <% if flash[:reminder] %>
    <p style="color: green;"><%= flash[:reminder] %></p>
  <% end %>
  <a href="step_three">step_tree</a>

app/views/rental/step_three.rhtml:

  <h1>Step three!</h1>
  <% if flash[:reminder] %>
    <p style="color: green;"><%= flash[:reminder] %></p>
  <% end %>
  <a href="step_one">step_one</a>

Discussion

As you can see in the solution, the controller creates a flash message only in the action called step_one.

From a browser, in the first step you see the reminder on the screen. When you click on the link at the bottom of the page, you call step_two. Now the flash message is shown a second time.

Step three is like step two, but we didn’t call the flash.keep in this method, and the message doesn’t reappear. The keep method holds the reminder for only one request.

See Also

• Recipe 4.5, “Displaying Alert Messages with Flash”