Reconnect to DB module using Sequel

sequel_db_reconnector.rb

require "singleton"
require "sequel"
=begin
Overview:
  Reconnect to DB module using Sequel
  When `ping` success, `connection` return same connection.
  In case of fail, reload `config/database.yml` and try new connect.

Require:
  `../config/database.yml` (Deploy in `lib/` (or other dir) this file.)

Usage:
  require "lib/THIS_FILE.rb"
  DB::Connector.instance.connection
  => #<Sequel::**::Database>

  a = DB::Connector.instance
  a.connection[:items]
  => <Sequel::**::Dataset: "SELECT * FROM \"items\"">

  # using Sequel::Model
  Sequel:Model.db = DB::Connector.instance.connection

Advanced(for short hand):
  require "lib/THIS_FILE.rb"
  include DB
  db
  => #<Sequel::**::Database>
  db[:items]
  => <Sequel::**::Dataset: "SELECT * FROM \"items\"">

  ** WARNING: If variable assign to `db`, it cannot use after. **
  db
  => #<Sequel::**::Database>
  db = 1
  db
  => 1 (Oh... T_T)

Limit:
  Under run the PostgreSQL only. (TDB)

config/database.yml:
development:
    adapter: postgres
    host: 127.0.0.1
    username: postgres
    password: postgres
    database: development_db
    min_messages: warn

test:
    adapter: postgres
    host: 127.0.0.1
    username: postgres
    password: postgres
    database: test_db
    min_messages: warn
=end
module DB
  class Connector
    include Singleton
    def initialize
      @c = File.join(File.expand_path(File.dirname(__FILE__)), "..", "config", "database.yml")
    end

    def ping
      @db[:pg_attribute].first
      true
    end

    def connection
      begin
        ping
      rescue
        dbconf = YAML.load(ERB.new(File.read(@c)).result)
        @db = Sequel.connect(dbconf[Sinatra::Base.environment.to_s])
      end
      @db
    end
  end

  def db
    DB::Connector.instance.connection
  end
  module_function :db
end