Updates inverse counter caches when #collection_singular_ids= is called for an object extending ActiveRecord::Base

distant_counters.rb

module DistantCounters
  extend ActiveSupport::Concern

  included do
    reflect_on_all_associations.each do |reflection|
      next unless reflection.macro == :has_many and reflection.is_a? ActiveRecord::Reflection::ThroughReflection
      next unless reflection.klass.column_names.include? "#{name.underscore.pluralize}_count"

      assoc_name = reflection.name.to_s.singularize
      redefine_method "#{assoc_name}_ids=" do |ids|
        counter_cache_key = "#{self.class.name.underscore.pluralize}_count"

        new_ids = ids.map(&:to_s).reject(&:empty?).map(&:to_i)
        old_ids = send "#{assoc_name}_ids"

        (old_ids - new_ids).each { |an_id| reflection.klass.decrement_counter counter_cache_key, an_id }
        (new_ids - old_ids).each { |an_id| reflection.klass.increment_counter counter_cache_key, an_id }

        association(assoc_name.pluralize.to_sym).ids_writer ids
      end
    end
  end

end