keyword.rb

  def bid_ids
    key[:bids].zrange(0, -1)
  end

  def bids
    bid_ids.map { |id| Bid[id] }
  end

  def add_bid(bid)
    key[:bids].zadd(bid.value, bid.id)
  end

  def remove_bid_id(id)
    key[:bids].zrem id
  end