Rails Flash message on the current request only

Sometimes all you want is to display a flash message for the current request template, i.e. it should not propagate to the next action. For example, I had an action where I wanted to warn the user that he had already processed a file:

def parse
    @upload = Upload.find(params[:id])
    if (@upload.processed_at)
      flash[:warning] = "This file has already been processed at " + @upload.processed_at.to_s(:long)
    end
end

The flash message is correctly shown at the parse.html.erb render, but it will also render on the next action processed. I do not want this to happen, so I have two options offered by the ActionController::Flash::FlashHash class.

First option is to use the now() method, which sets a flash that will not be available to the next action, only to the current.

flash.now[:warning] = "This file has already been processed at " + @upload.processed_at.to_s(:long)


The other option is the discard() method, which marks the entire flash or a single flash entry to be discarded by the end of the current action.

flash.discard                    # discard the entire flash at the end of the current action
flash.discard(:warning)   # discard only the "warning" entry at the end of the current action