Source: http://www.devmynd.com/blog/2013-6-automatic-scopes-and-indexing-hstore?utm_source=postgresweekly&utm_medium=email

hstore_accessor.rb

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

  module ClassMethods
    def hstore_accessor(hstore_attribute, *keys)
      Array(keys).flatten.each do |key|
        define_method("#{key}=") do |value|
          send("#{hstore_attribute}=", (send(hstore_attribute) || {}).merge(key.to_s => value))
          send("#{hstore_attribute}_will_change!")
        end
        define_method(key) do
          send(hstore_attribute) && send(hstore_attribute)[key.to_s]
        end
        ###Right here
        send(:scope, "for_#{key}", -> value { where("#{hstore_attribute} -> '#{key}'=?", value.to_s)})
      end
    end
  end
end

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