Tag: Ruby

Careful with that email

When you are building systems like my Keep on Posting or my DNSk9 that send emails there’s always the danger that you’ll accidentally fire emails from your development machine to real users. You really don’t want to do that because it’s annoying and extremely unprofessional.

It happened to me a couple of times. Thankfully, nothing serious. But I learned the lesson. That’s why in my user models now I have a safe_email method which I use instead of accessing email whenever I’m about to actually deliver a message.

The method safe_email ensures that nobody will receive a message unless I’m in production and at the same time it’s good for testing. Obviously most of the time in development and testing mode I don’t deliver emails at all, but sometimes, I make an exception:

def safe_email
  if Rails.env.production? || email.blank? # If the email is blank (or nil), let it be.
    email
  else
    "pupeno+#{email.gsub("@", "_AT_")}@pupeno.com"
  end
end

Rake tasks for production

When I need to run something periodically on production, I always implement it as a rake tasks and install it as a cron job. Nevertheless there’s some setup to do in the task to have proper logging and error reporting.

This is the template I use for creating those tasks:

namespace :projectx do
  desc "Do something"
  task :something => :environment do
    if Rails.env.development?
      # Log to stdout.
      logger = Logger.new(STDOUT)
      logger.level = Logger::INFO # DEBUG to see queries
      ActiveRecord::Base.logger = logger
      ActionMailer::Base.logger = logger
      ActionController::Base.logger = logger
    else
      logger = ActiveRecord::Base.logger
    end

    begin
      logger.info "Doing something"
    rescue Exception => e
      HoptoadNotifier.notify(e)
      raise e
    end
  end
end

While in development mode, it outputs to the console for convenience.

Another useful collection method? Enumerable#select_first

For a personal project I’m working on, I need to find out the smallest time period with more than 5 records. I essentially wrote this code:

period = [1.week, 1.month, 1.year].select_first do |period|
  Record.where("published_at >= ?", period.ago).count >= 5
end

only to find out that the select_first method doesn’t exist. So I wrote it:

module Enumerable
  def select_first(&predicate)
    self.each do |item|
      if yield(item)
        return item
      end
    end
    return nil
  end
end

and then of course, I tested it:

require "test_helper"

require "enumerable_extensions"

class EnumerableTest  2 }
  end

  should "select_first the first one" do
    assert_equal 1, [1, 2, 3, 4].select_first { |i| i >= 1 }
  end

  should "select_first the last one" do
    assert_equal 4, [1, 2, 3, 4].select_first { |i| i >= 4 }
  end

  should "select_first none" do
    assert_equal nil, [1, 2, 3, 4].select_first { |i| i >= 100 }
  end
end

A hash map method that returns a hash

I’ve just released another gem, this one extends Hash to contain another method called hmap. This solves a problem I face ofter: how to run a map in a hash that returns another hash, for example:

{:a => 1, :b => 2, :c => 3}

being converted into

{:a => 2, :b => 3, :c => 4}

With hmap it’s easy:

hash.hmap { |a,b| {a => b + 1} }

It also works with arrays, but you must make sure the array you return always contains two and only two elements:

hash.hmap { |a,b| [a, b + 1] }

And that’s all, quite a simple piece of code, but now it’s re-usable and well tested.

Faking it: enums in Ruby

Ruby doesn’t have enums and in Rails I sometimes need it. I’ve come out with my own way of doing after some trial and error. First I want to be able to access these enums as constants in a class, like:

Pizza::RAW
Pizza::COOKED
Pizza::BOXED
Pizza::DELIVERED
Pizza::EATEN

That’s actually quite easy:

class Pizza
  RAW = 1
  COOKED = 2
  BOXED = 3
  DELIVERED = 4
  EATEN = 5
end

If I’m storing those values on the database, I’d like to have my database be more readable, so, I just store strings:

class Pizza
  RAW = "raw"
  COOKED = "cooked"
  BOXED = "boxed"
  DELIVERED = "delivered"
  EATEN = "eaten"
end

That’s not very efficient and there are better ways these days. But it’s simple and premature optimization is the root of all evil. Anyway, back to Ruby, I’d like to be able to get a list of all possible enum values, to be able to populate selections for example:

class Pizza
  RAW = "raw"
  COOKED = "cooked"
  BOXED = "boxed"
  DELIVERED = "delivered"
  EATEN = "eaten"

  STATES = [RAW, COOKED, BOXED, DELIVERED, EATEN]
end

Simple enough except that it doesn’t follow DRY style. In Ruby we can do better:

class Pizza
  STATES = [
    RAW = "raw",
    COOKED = "cooked",
    BOXED = "boxed",
    DELIVERED = "delivered",
    EATEN = "eaten"
  ]
end

That defines the constant and since the result of RAW = "raw" is "raw" we can also add it to an array at the same time.

John, the manager of the Ruby Pizza Shop was concerned that some pizzas were devoured immediately and others took as long as 15 minutes. Decided to improve his business he started investigating the whole procedure and he noticed that as soon as the pizza left the kitchen, some cooks considered delivered and marked them as such. That was wrong so instead of doing a pizza-state training, he decided we should improve the UI. Let’s describe the state.

class Pizza
  STATES = [
    RAW = "raw",
    COOKED = "cooked",
    BOXED = "boxed",
    DELIVERED = "delivered",
    EATEN = "eaten"
  ]

  STATE_EXPLANATIONS {
    RAW => "The pizza is not a pizza yet, just a bunch of ingredients.",
    COOKED => "OMG! That smells good!",
    BOXED => "It's ready to go.",
    DELIVERED => "The pizza has been snatched out of the hands of a delivery boy.",
    EATEN => "The pizza is no more."
  }
end

Of course we can do better than that and merge it in one:

class Pizza
  STATE {
    (RAW = "raw") => "The pizza is not a pizza yet, just a bunch of ingredients.",
    (COOKED = "cooked") => "OMG! That smells good!",
    (BOXED = "boxed") => "It's ready to go.",
    (DELIVERED = "delivery") => "The pizza has been snatched out of the hands of a delivery boy.",
    (EATEN = "eaten") => "The pizza is no more."
  }
end

Stylistically I’m not a fan, but semantically, that’s dryer. Now, we can get the list of states like this:

Pizza::STATE.keys

Metaprogramming Ruby

There are thousands of books that will take you from illiterate to novice in any programming language. But finding those that will take you from novice or intermediate to expert is hard. I remember reading Effective Java some years ago and wishing I had something like that for Python. I’ve never found one.

Metaprogramming Ruby is a great book full of very interesting knowledge, full of those things that separate a Ruby programmer and an export Ruby programmer. Before finishing the book I’ve already put to use some of the lessons and it saved me a lot of time. The book payed for itself before I’ve finished reading and I really recommend it to anyone who is serious about coding in Ruby.

The magic of Bundler

Recently I reported a bug for Formtastic. Justin French, the author of Formtastic, created a branch and made a fix. He then asked me for my feedback.

I look at the code and then decided to give it a try. In a pre-Bundler world that would have required this:

  1. Find a directory to play with this.
  2. Clone the Formtastic repository with Git from http://github.com/justinfrench/formtastic.git
  3. Create a local branch tracking the remote branch with the fix, GH-264. This is something I don’t do often enough with Git and every time I have to look it up.
  4. Figure out how to build a gem out of it. Is it rake? is it rake build? is it rake gem? This might also fail and need fixing some stuff.
  5. Install said gem, which is not that trivial. Should I install as my user or as root? Should I remove the currently installed version of the gem? If the branch didn’t have an increase in version number it could be problematic.
  6. Test my application. Make sure it’s picking up the new gem.
  7. Uninstall the gem, maybe re-install the stock gem.
  8. Delete the temporary directories I’ve created to hold the cloned repository (this is something I always forget to do and a month later I’m wondering: what’s this? is there any important changes I’ve did in this repo?).
  9. The tasks are not that big, but are very inconvenient to do and uncomfortable for a perfectionist like me. Thankfully I’m using Bundler, so the above was like this:

  1. Add :git => "http://github.com/justinfrench/formtastic.git", :branch => "GH-264" to the Formtastic line in Gemfile.
  2. Run bundle install.
  3. Test app.
  4. Revert the Gemfile change.
  5. Run bundle install.
  6. I really love Bundler.

Redirecting back

It’s very common in Rails CRUD to have a create and update actions that redirect back to the show action. The idea is that you show an object, click edit, save, go back to showing said objects with your changes.

All is fine until you have an edit link somewhere else. Let’s say you have an edit link in the listing of the CRUD, when someone uses you have to go back to the listing, not the show.

Well, Ruby on Rails provides just the thing for that:

redirect_to :back

That will send you back wherever you came from. The problem with that is that it will raise an exception if there’s no HTTP_REFERER, so you’ll have to write something like this:

begin
  redirect_to :back
rescue ActionController::RedirectBackError
  redirect_to somewhere_else
end

Of course there’s a pattern, so almost all my projects, at one time or another end up with this snippet of code in the application controller:

def redirect_back_or_to(*args)
  redirect_to :back
rescue ActionController::RedirectBackError
  redirect_to *args
end

I really like how every method is an implicit begin, it really looks beautiful. Then you just do:

redirect_back_or_to somewhere_else

I’m surprised Rails didn’t come with something like that out of the box, or maybe I just missed.

fofof was useless

It’s always hard to kill your own code, but not killing it when you have to is worst in the long run. My idea for fof and consequently my gem fofof was useless.

First I’ve discovered it didn’t work at all with the new Rails 3 query syntax. When I started to find a fix I’ve discovered I could replace the whole thing with:

 || raise(NotFound.new)

The examples in the Find or 404 post would end up like:

Blog.find_by_id(id) || raise(NotFound.new)

and

blog = Blog.fof.find(blog_id)
post = blog.posts.find_by_id(id) || raise(NotFound.new)

It’s less code, it’s more robust, I even think it’s much more readable. So there you, I’m killing fofof.