comment.rb

class Comment < ActiveRecord::Base
  
  belongs_to :post
  
  named_scope :by_quality, {:order => 'quality DESC'}
  named_scope :by_created_at, {:order => 'created_at DESC'}
end

comments_controller.rb

class CommentsController < ApplicationController
  
  before_filter :find_post
  
  def index
    @comments = case params[:filters]
      when 'by_quality'    : @post.comments_by_quality(params[:page])
      when 'by_created_at' : @post.comments_by_created_at(params[:page])
      else
        @post.comments_by_quality(params[:page])
      end
  end
  
  private
  
  def find_post
    @post = Post.find(params[:post_id])
  end
end

comments_helper.rb

class CommentsHelper
  
  TYPE_MAP = {
    :by_quality => "order by quality",
    :by_created_at => "order by date"
  }
  
  def link_to_filtered(comments, type)
    # WHAT WOULD BE A GOOD WAY OF DOING THIS "current_type" method on the comments array?
    if comments.current_type == type
      TYPE_MAP[type]
    else
      link_to TYPE_MAP[type], post_comments_path(:filters => type)
    end
  end
end

# So that in the view I can do:
# link_to_filtered(@comments, :by_quality)
# link_to_filtered(@comments, :by_created_at)

post.rb

class Post < ActiveRecord::Base

  has_many :comments

  def comments_by_quality(page)
    comments.by_quality.paginate(:page => page, :per_page => 30)
  end

  def comments_by_created_at(page)
    comments.by_created_at.paginate(:page => page, :per_page => 30)
  end
end