resource.rb

require 'sequel'

DB ||= Sequel.connect ENV['DATABASE_URL']

class Resource < Sequel::Model
  include Sequel.inflections

  def after_save
    db.notify channel
  end
  
  def listen
    db.listen channel, loop: true do |channel, pid, payload|
      yield channel
    end
  end
  
  def channel
    [self.class.table_name, id].join '_'
  end
end

server.rb

require 'sinatra'
require 'json'

require_relative 'resource'

configure do
  mime_type :event_stream, 'text/event-stream'
end

get '/:id/stream', provides: :event_stream do
  stream do |out|
    resource.listen do |channel|
      out << message(event: channel, data: resource.reload)
      break if out.closed?
    end
  end
end

def resource
  @resource ||= Resource[params[:id]]
end

def message(event:, data:)
  "event: %s\ndata: %s\\n" % [event, data.to_json]
end

test.rb

require 'securerandom'

require_relative 'resource'

loop do
  Resource[2].update title:  SecureRandom.hex
  sleep 5
end