EM::PG

One more EventMachine wrapper for Postgresql pg-lib.

Features

  • Fully async including connect and right usage of #busy and #consume_input;
  • All results are standard deferrable objects;
  • Distinct exceptions hierarchy;
  • Wrapper for Green and adapter fot Sequel.

Usage

gem "em-pg"

require "em/pg"

EM.run do
  db = EM::PG.new host: "localhost", port: 5432, dbname: "test", user: "postgres", password: "postgres"
  db.callback do
    q = db.send_query "select 1"
    q.callback do |res|
      puts "RESULT: #{res.inspect}"
      EM.stop
    end
    q.errback do |e|
      raise e
    end
  end

  db.errback do |e|
    raise e
  end
end

To all errbacks pass one argument, instance of EM::PG::Error. So it easy to write common handlers and wrappers for something like EM-Synchrony and Green.

Supported methods

  • send_query
  • send_prepare
  • send_query_prepared
  • send_describe_prepared
  • send_describe_portal

All have same semantics as in pg-lib, but result is a Deferrable object

Disconnects

On disconnect all current queries will be failed with exception DisconnectError. You also can pass :on_disconnect callback with options, wich will be called before queries errbacks.

EM::PG doesn't have reconnect strategy, you should handle disconnects by youself.

Logging

You can pass :logger option or set EM::PG.logger for all instances.

Exceptions

 EM::PG::Error
   ConnectionRefusedError
   DisconnectError
   BadStateError
   UnexpectedStateError
     BadConnectionStatusError
     BadPollStatusError
   PGError
  • ConnectionRefusedError - can't connect. Have field .message with reason;
  • DisconnectError - connection disconnected. Will be raised on all uncompleted queries;
  • BadStateError - you try do something while a wrong state. For example send query on not connected client;
  • UnexpectedStateError - something gone wrong :(
  • PGError - original PG exceptions was raised. Have field .original.

See also