application.js

$('#nextmonth').on('click', fuction(e)) {
	$.get('/rota_days/show.json?mon=12').success(function(data) {
		rota_days = data

		for ( i = 0; i < rota_days.length; i++) 
		{
			rota_day = rota_days[0];
			/* doing stuffs with rota_day */			
		}
	});
)};
	

index.html.erb

<table class = "rota">
	<thead>
		<th>Date</th> 
		<% @hospitals.each do |hosp| %>
		<th><%= hosp.name%></th>
		<% end %>
	</thead>
	<tbody>
		<% @dates.each do |date| %>
		<tr>
			<td><%= date.to_s(:short) %></td>
			<% (1..@hospitals.count).each do %> 
				<td></td> 
			<% end %> 
		   </tr> 
			<% end %>
	</tbody>
</table>

<%= link_to 'Next Month', rota_days_path(:month => 12), :id => 'nextmonth' %> 

rota_days_controller.rb

class RotaDaysController < ApplicationController
  # GET /rota_days
  # GET /rota_days.json
  # load_and_authorize_resource
  respond_to :json, :html
 
  def index
    @rota_days = RotaDay.all
    # @dates = @rota_days.collect(&:day)
    @hospitals = Hospital.all
    t1 = Date.today.at_beginning_of_month
    t2 = Date.today.end_of_month
    @dates = (t1..t2).to_a 
    
    @title = "Rota"
   
    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @rota_days }
    end
  end

  def nextmonth
    dfrom = Date.parse("#{Date.today.year}-#{sprintf("%02d", params[:mon].to_i)}-01")
    dto = Date.parse("#{Date.today.year}-#{sprintf("%02d", params[:mon].to_i + 1)}-01") 
    @rota_days = RotaDay.where('rota_days.day BETWEEN ? AND ?', dfrom, dto)
    respond_with(@rota_days)
  end 
end