Module, metaprogramming, dynamic instance/class method definition

gistfile1.txt

# Usage:
# class YourClass < ApplicationRecord
#   denormalizable_collection :my_collection
#   ...
#
#   def self.my_collection_data
#     self.where(...).limit(5)
#   end
# end

# View:
# <%= News.my_collection.each do ... %>

module DenormalizableCollection
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def denormalizable_collection(*actions)
      actions.each do |action|
        generate_class_methods(action)
        generate_instance_methods(action)
        generate_callbacks(action)
      end
    end

    def generate_class_methods(action)
      self.class_eval do |klass|
        klass.define_singleton_method "#{action}" do
          collection = Redis.current.get(send("#{action}_key"))

          return [] unless collection.present?

          JSON.parse(collection).map { |h| DenormalizedHash.new(h) }
        end

        klass.define_singleton_method "set_#{action}" do
          Redis.current.set(send("#{action}_key"), send("#{action}_data").to_json)
        end

        klass.define_singleton_method "#{action}_data" do
          raise NotImplementedError, "#{action}_data is required"
        end

        klass.define_singleton_method "#{action}_key" do
          "#{name.underscore}_#{action}".to_sym
        end
      end
    end

    def generate_isntance_methods(action)
      self.class_eval do |klass|
        klass.define_method "resync_#{action}" do
          self.class.send("set_#{action}".to_sym)
        end
      end
    end

    def generate_callbacks(action)
      self.class_eval do
        after_commit "resync_#{action}".to_sym
        after_destroy "resync_#{action}".to_sym
        
        # ... or 
        # after_commit -> { self.class.send("set_#{action}".to_sym) }
        # after_destroy -> { self.class.send("set_#{action}".to_sym) }
      end
    end
  end
end