module Mongoid
  module CounterCache
  	module ClassMethods
  	  def counter_cache(meta_data)
  	  	counter_name = "#{meta_data[:inverse_of]}_count"

  	  	set_callback(:create, :after) do |document|
  	  	  relation = document.send(meta_data[:name])

  	  	  if relation
  	  	  	relation.inc(counter_name.to_sym => 1) if relation.class.fields.keys.include?(counter_name)
  	  	  end
  	  	end

  	  	set_callback(:destroy, :after) do |document|
  	  	  relation = document.send(meta_data[:name])

  	  	  if relation && relation.class.fields.keys.include?(counter_name)
  	  	  	relation.inc(counter_name.to_sym => -1)
  	  	  end
  	  	end
  	  end
  	end
  end
end 
Add the counter cache module to cache the replies count to increase performance.
Add the counter cache module to cache the replies count to increase performance.
