PostgreSQL LISTEN/NOTIFY example for ruby

pg_pub_sub.rb

#
# A:
# pubsub = PgPubSub.new('channelname')
# pubsub.subscribe do |data|
#  puts "data: #{data} is coming!"
# end
#
# B:
# pubsub = PgPubSub.new('channelname')
# pubsub.publish("hello world")
# 
# becomes
# A:
# => data: hello world is coming!
#
#
# "C" before channel name is not required.
# But when channel name starts with digit, e.g. LISTEN 1NAME
# it causes syntax error. So, it fix erorr.
#
class PgPubSub
  def initialize(channel)
    @channel = channel
  end
  def subscribe
    connection.execute "LISTEN C#{@channel}"
    loop do
      connection.raw_connection.wait_for_notify do |event, id, data|
        yield data
      end
    end
  ensure
    connection.execute "UNLISTEN C#{@channel}"
  end
  def publish(json)
    connection.execute "NOTIFY C#{@channel}, #{connection.quote json}"
  end

  private
  def connection
    ActiveRecord::Base.connection
  end
end