Redirect and still show error messages

gistfile1.rb

# app/controllers/ballots_controller.rb
def create
  @ballot = Ballot.new(params[:ballot])
  if @ballot.save
    redirect_to @ballot, :notice => 'Successful'
  else
    session[:error_messages] = @ballot.errors.full_messages
    redirect_to edit_ballot_path(@ballot, :params => params), :notice => 'Ruh Roh!'
  end
end

# /app/views/ballots/edit.html.erb
<% if session[:error_messages] %>
  <ul class="validation_errors">
    <% session[:error_messages].each do |message| %>
      <li><%= message %></li>
    <% end %>
  </ul>
<% end %>