Ruby on Rails

if i click on month i want to display only that months blog posts,this  is an existing code which is working fine for few months not for  all,where am i doing wrong ,should i change the code.can any one help me  out.and also i want the month and date to display in reverse ,recent on  top.like        ARCHIVES      January 2015      December 2014      November 2014      October 2014      September 2014      August 2014      June 2014      May 2014      .      .    app/blogcontroller.rb        class BlogController < ApplicationController        require 'date'      if (params[:population_categories])        @blog_posts = BlogPost.live.where(:population_category_ids  =>params[:population_categories]).latest.page(params[:page])       elsif (params[:month])        b_dt = DateTime.strptime("01/" + params[:month].to_s + "/" +  params[:year] + " 00:00", "%d/%m/%Y %H:%M")        e_dt = DateTime.strptime("01/" + (params[:month].to_i+1).to_s +  "/" + params[:year] + " 00:00", "%d/%m/%Y %H:%M")        else  @blog_posts=BlogPost.live.keyword(params[:keyword]).latest.page(params[:page])      end        app/views/blog/index.html.erb        <div class="right-col">      <h2>ARCHIVES</h2>      <div class='posts_by_month'>          <ul>        <% archive_string = "" %>        <% date_value = "" %>        <% @posts_by_month.each do |monthname, posts| %>            <% date_value = (Date::MONTHNAMES[monthname[0..-6].to_i]) + " "  + (monthname[3..8]) %>          <% archive_string = "<li><a class='filter' href='/blog?month=" +  monthname[0..-6] + "&year=" + monthname[3..8] + "'>" + date_value +  "</a></li>" + archive_string %>        <% end %>        <%= raw archive_string %>        </ul>          </div>    </div>