Modify hstore accessor to allow some typing

hstore_accessor.rb

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

  VALID_TYPES = [:string, :integer, :float, :array, :hash]
  SERIALIZERS = {
    :array => ->(val) { val.to_json },
    :hash => ->(val) { val.to_json }
  }

  DESERIALIZERS = {
    :array => ->(val) { JSON.parse(val) },
    :hash => ->(val) { JSON.parse(val) },
    :integer => ->(val) { val.to_i },
    :float => ->(val) { val.to_f }
  }

  InvalidDataTypeError = Class.new(StandardError)

  module ClassMethods
    def hstore_accessor(hstore_attribute, fields)
      fields.each do |key, type|

        raise InvalidDataTypeError unless VALID_TYPES.include?(type)

        define_method("#{key}=") do |value|
          serialized_value = value.to_s
          if SERIALIZERS.has_key? type
            serialized_value = SERIALIZERS[type].call(value)
          end

          send("#{hstore_attribute}=", (send(hstore_attribute) || {}).merge(key.to_s => serialized_value))
          send("#{hstore_attribute}_will_change!")
        end

        define_method(key) do
          deserialized_value = value = send(hstore_attribute) && send(hstore_attribute)[key.to_s]
          if DESERIALIZERS.has_key? type
            deserialized_value = DESERIALIZERS[type].call(value)
          end

          deserialized_value
        end

        send(:scope, "for_#{key}", -> value { where("#{hstore_attribute} -> '#{key}'=?", value.to_s)})
      end
    end
  end
end

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

usage.rb

class Car < Vehicle
  hstore_accessor :data,
                  exterior_color: :integer,
                  interior_color: :string,
                  transmission: :string,
                  drive_type: :string,
                  fuel_type: :hash,
                  door_count: :integer,
                  car_type: :string,
                  options: :array
end