ruby-pg-em connection pool deferred transaction example

gistfile1.rb

#!/bin/env ruby
require 'pg/em/connection_pool'

# psql test <<EOF
# CREATE TABLE bar (
#     key integer,
#     value character varying
# );
# EOF
EM.run do
  pool = PG::EM::ConnectionPool.new(size: 5, lazy: true, dbname: 'test')

  pool.query_defer('DELETE FROM bar').callback do

    timer = EM.add_periodic_timer(0.2) do
      pool.query_defer("SELECT * FROM bar WHERE key = 69").callback do |res|
        puts res.to_a.inspect
      end.errback {|ex| raise ex }
    end

    EM.add_timer(2) do
      pool.__send__(:hold_deferred) do |conn|
        EM::DefaultDeferrable.new.tap do |df|
          rollback = proc do |ex|
            conn.query_defer("ROLLBACK") { df.fail(ex) }
          end
          conn.query_defer("BEGIN").callback do
            conn.query_defer("INSERT INTO bar (key,value) VALUES (69,'foo')").callback do
              conn.query_defer("UPDATE bar SET value = 'xyz' WHERE key = 69").callback do
                conn.query_defer("COMMIT").callback { df.succeed }.errback(&rollback)
              end.errback(&rollback)
            end.errback(&rollback)
          end.errback {|ex| df.fail(ex) }
        end
      end.callback do
        puts "transaction commit good"
          EM.add_timer(2) { EM.cancel_timer timer; EM.stop }
      end.errback do |ex|
        puts "transaction failed"
        EM.add_timer(2) { raise ex }
      end
    end

  end.errback do |ex|
    raise ex
  end
end