After reading Scripting Java Libraries With Ruby on the Engine Yard

Ruby5 is a new twice weekly podcast dedicated to Ruby and Rails news. It's headed by Gregg Pollack (formerly of the RailsEnvy podcast which Jason Seifer has now taken over) and Nathan Bibler. They aim to cover several bits of Ruby and Rails news in five minutes.

Limitare il numero di di query SQL è uno dei modi migliori per migliorare la performance di un'applicazione Rails, e l'eager loading è probabilmente il modo migliore per farlo.

Il problema

Supponiamo di trovarci nella seguente situazione molto comune: si ha bisogno di un'applicazione Rails con il model Person. Ogni persona ha più amici (has_many...friends). Cosa si deve fare per trovare gli amici di una persona?

Polymorphic Relationships

Le Polymorphic relationships permettono di avere un singolo modello associato a un numero arbitrario di altri modelli.

Esempio

Ad esempio, supponiamo di avere un database di contatti che utilizza due modelli, Person e Company. Entrambi Persons e companies hanno degli indirizzi che si vogliono conservare nel database, e si vuole poter interrogare tutti gli indirizzi in un colpo solo (tipo per una ricerca basata su un luogo).

Since we launched Issues so many months ago, many users have asked for a way to see all the issues spread across all their repos. We don’t have a page for this on GitHub yet, but the information is exposed via the API.

What you want another drinkup? Fine, but this is the last one for the year. Primarily because the next slated drinkup Thursday would fall on December 31st, and if you somehow dont know or perhaps are still under the respective drinking age in your country, everywhere is a drinkup that day.

Chris Wanstrath makes a good point about an ugly way to initialize a variable, but I don't agree that an explicit return is the best style to use.

The original ugly:

def logger
  unless @logger
    @logger = Logger.new(STDOUT)
    @logger.level = Logger::WARN
  end
  @logger
end

Chris' improvement:

def logger
  return @logger if defined? @logger
  @logger = Logger.new(STDOUT)
  @logger.level = Logger::WARN
  @logger
end

I prefer a functional style:

Introduction

Before answering what is EventMachine, first I will try to explain the problem that EventMachine solves.

A network server like http server or chat server usually works in a threaded model. What it means is that on a particular port, a process is listening for connections. When a client makes a connection then this process spawns a new thread and that thread is handed over the task of responding to that client. If server is getting too much traffic then the number of threads created by the main process goes up very quickly.