render/redirect_to with flash messages and validation errors in rails 4

contact.html.erb

<div>
	<%= form_for(@entrant, url: contact_path) do |f| %>

		<% if !flash.empty? %>
			<div id="flash">
		    <% flash.keys.each do |k| %>
		        <div class="<%= k %>">
		            <%= flash[k] %>
		        </div>
		   <% end %>
			</div>
		<% end %>

		<% if @entrant.errors.any? %>
		    <div id="error_explanation">
		      <h2><%= pluralize(@entrant.errors.count, "error") %> prohibited this entrant from being saved:</h2>
		      <ul>
		      <% @entrant.errors.full_messages.each do |msg| %>
		        <li><%= msg %></li>
		      <% end %>
		      </ul>
		    </div>
	  	<% end %>

		<div class="field">
			<%= f.label :name %><br>
			<%= f.text_field :name %>
		</div>
		<div class="field">
			<%= f.label :email %><br>
			<%= f.text_field :email %>
		</div>
		<div class="actions">
			<%= f.submit %>
		</div>
	<% end %>
</div>

entrant.rb

class Entrant < ActiveRecord::Base
  validates :email, presence: true
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  validates :email, presence: true, format: { with: VALID_EMAIL_REGEX }

  has_many :events, :through => :event_maps
  has_many :event_maps, :foreign_key  => "entrant_id"
  accepts_nested_attributes_for :events, :reject_if => :all_blank
end

PagesController.rb

class PagesController < ApplicationController

  def contact
   if request.post? #POST

     logger.info("I am a POST")

     @entrant=Entrant.new(entrant_params)
     @event = Event.find(1)

     respond_to do |format|
	if @entrant.save
          @event.entrants << @entrant
          format.html { redirect_to :back, notice: 'Entrant was successfully created and registered.' }
          logger.info("I am saved")
          format.js
        else
	  logger.info("I am invalid")

          #DOES NOT WORK FLASH NEEDS TO BE SET FIRST
          #format.html { render action: 'contact', notice: 'Entrant was successfully created and registered.' }

          #THIS IS HOW IT IS DONE
	  format.html { flashme("I am invalid", 'contact') } #CALLING FLASHME FUNCTION 
         
	  format.js
        end
     end

   else #GET
     logger.info("I am a GET")
     @entrant=Entrant.new
   end
  end

  private
    # Never trust parameters from the scary internet, only allow the white list through.
    def entrant_params
      params.require(:entrant).permit(:name, :email)
    end

    # THIS SETS A FLASH MESSAGE BEFORE THE RENDER
    # ERRORS ARE ALSO SEND TO THE VIEW SINCE WE'RE REFRESHING
    def flashme(msg, action)
    	# FLASH MUST BE SET !BEFORE! RENDER ACTION
     	flash[:error] = msg
    	render action: action
    end
end