has_counter_cache_on is a simple ActiveRecord extension which allows you to have multiple counters for a single association, counted when simple conditions are met

has_counter_cache_on.rb

# has_counter_cache_on is a simple ActiveRecord extension
# which allows you to have multiple counters for a single
# association, counted when simple conditions are met
#
# The implementation is adapted from the current
# add_counter_cache_callbacks code in Rails.
#
# Example:
#
# class Submission < ActiveRecord::Base
# end
#
# class Vote < ActiveRecord::Base
#   belongs_to :submission, counter_cache: :votes_count
#   has_counter_cache_on :submission, :upvotes_count, support: true
#   has_counter_cache_on :submission, :downvotes_count, support: false
# end
#
module HasCounterCacheOn
  extend ActiveSupport::Concern

  module ClassMethods
    def has_counter_cache_on(association, cache_column, conditions)
      association = self.reflect_on_association(association)
      model = association.active_record
      name = association.name

      method_name = "belongs_to_counter_cache_after_create_for_#{name}_#{cache_column}"
      model.redefine_method(method_name) do
        record = send(name)
        record.class.increment_counter(cache_column, record.id) if record && conditions.all? {|k, v| send(k) == v }
      end
      model.after_create(method_name)

      method_name = "belongs_to_counter_cache_before_destroy_for_#{name}_#{cache_column}"
      model.redefine_method(method_name) do
        record = send(name)
        record.class.decrement_counter(cache_column, record.id) if record && conditions.all? {|k, v| send(k) == v }
      end
      model.before_destroy(method_name)

      model.send(:module_eval,
        "#{association.class_name}.send(:attr_readonly,\"#{cache_column}\".intern) if defined?(#{association.class_name}) && #{association.class_name}.respond_to?(:attr_readonly)", __FILE__, __LINE__
      )
    end
  end
end

ActiveRecord::Base.send(:include, HasCounterCacheOn)