The following example implements a Redis store to save exchange rates to a redis database.

redis_rate_store.rb

class RedisRateStore
  INDEX_KEY_SEPARATOR = '_TO_'.freeze
  
  # Using second db of the redis instance
  # because sidekiq uses the first db
  REDIS_DATABASE = 1
  
  # Using Hash to store rates data
  REDIS_STORE_KEY = 'rates'

  def initialize
    conn_url = "#{Rails.application.credentials.redis_server}/#{REDIS_DATABASE}"
    @connection = Redis.new(url: conn_url)
  end

  def add_rate(iso_from, iso_to, rate)
    @connection.hset(REDIS_STORE_KEY, rate_key_for(iso_from, iso_to), rate)
  end

  def get_rate(iso_from, iso_to)
    @connection.hget(REDIS_STORE_KEY, rate_key_for(iso_from, iso_to))
  end

  def each_rate
    rates = @connection.hgetall(REDIS_STORE_KEY)
    return to_enum(:each_rate) unless block_given?

    rates.each do |key, rate|
      iso_from, iso_to = key.split(INDEX_KEY_SEPARATOR)
      yield iso_from, iso_to, rate
    end
  end

  def transaction
    yield
  end

  private

  def rate_key_for(iso_from, iso_to)
    [iso_from, iso_to].join(INDEX_KEY_SEPARATOR).upcase
  end
end