Handle connection for ActiveRecord subclasses

connection_handler.rb

require "active_record/base"

module ConnectionHandler
  class << self
    def establish_connections
      connection_classes.each(&:establish_connection)
    end

    def disconnect_all!
      connection_classes.map(&:connection).each(&:disconnect!)
    end

    private

    def connection_classes
      [ActiveRecord::Base] + base_classes_with_own_connection
    end

    def base_classes_with_own_connection
      ActiveRecord::Base.subclasses.select do |klass|
        klass.method(:establish_connection).owner == (class << klass; self; end)
      end
    end
  end
end

If you have multiple database connection using ActiveRecord, it's a good practice to define a base class for each connection which overrides the establish_connection method. In this way, all models that uses this will reuse the same connection. Otherwise each model will create its own connection.
If you get more of these, it quickly get cumbersome to handle disconnecting and reconnecting in forking applications like Unicorn or Resque. This class wraps the handling of this, so you only need one call.