ExtraValue.rb

# Each record of this class store one extra attribute for each model
# Used to store not important data need for reports, data sync, and etc
class ExtraValue < ActiveRecord::Base
  belongs_to :record, polymorphic: true

  scope :type, ->(klass){ where(record_type: klass) }
  scope :record, ->(r){ where(record_id: r.id, record_type: r.class) }

  class << self

    # usage: set(record, 'extra_attr', "text")
    # @param type - column type
    def set(record, name, value, type: :s)
      connection.execute(
        "INSERT INTO #{table_name} (record_id, record_type, `name`, value_#{type}) VALUES (#{connection.quote record.id}, #{connection.quote record.class.to_s}, #{connection.quote name}, #{connection.quote value}) ON DUPLICATE KEY UPDATE value_#{type} = #{connection.quote value}"
      )
    end

    def get(record, name)
      ExtraValue.record(record).where(name: name).pluck(:value_s).first
    end

  end

  # use in AR models
  # extra_value_attr :extra_name
  module Attribute
    def extra_value_attr(attr_name, type: :s)
      mixin = Module.new do

        define_method(attr_name) do
          ExtraValue.get(self, attr_name)
        end

        define_method("#{attr_name}=") do |v|
          ExtraValue.set(self, attr_name, v, type: type)
        end

      end
      prepend mixin
    end
  end
end

# == Schema Information
#
# Table name: extra_values
#
#  id          :integer          not null, primary key
#  record_id   :integer          not null, indexed => [record_type, name]
#  record_type :string(255)      not null, indexed => [record_id, name]
#  name        :string(255)      not null, indexed => [record_id, record_type]
#  value_s     :string(255)
#