How to Install ‘therubyracer’ or ‘libv8’ gem(s) on OSX

Recently, I need to move some Rails projects I was working on to new computer and this needs me to install all the dependencies for these projects.  While using bundler to install the gems; I encountered the following error:

extconf failed, exit code 1
Gem files will remain installed in /Users/ash/.rvm/gems/ruby-2.2.1/gems/libv8- for inspection.
Results logged to /Users/ash/.rvm/gems/ruby-2.2.1/extensions/x86_64-darwin-14/2.2.0-static/libv8-

An error occurred while installing libv8 (, and Bundler cannot continue.
Make sure that `gem install libv8 -v ''` succeeds before bundling.

Fortunately, with homebrew fixing this (on OSX 10.11, El Capitan at least) worked perfectly. Simply execute these commands:

brew install v8
gem install therubyracer
gem install libv8 -v '' -- --with-system-v8

Estabilishing ActiveRecord Database Connections in Ruby (But Without Rails)

Anyone who has even the smallest amount of experience developing with Ruby on Rails knows that Rails has some pretty sweet configuration conventions which make switching between environments very easy. Switching from development to production to testing is as easy as changing the RAILS_ENV variable. No doubt Rails does some dark magic behind the scenes to trivialise this. But what if you’re writing an app in Ruby, without the Rails to guide you?

ActiveRecord 101

Establishing a database connection in ActiveRecord without Rails is pretty basic:

require 'active_record'

  adapter:  'sqlite3',
  database: 'db/test.sqlite3'

It establishes a connection to the specified database with the specified connection  configuration. If you were using MySQL or PostgreSQL you would provide the relevant configuration such as username, password and host. With the connection established, we can now start consuming the connection however we like. For example, we may want to use funky Rails’ style models (so we can easily create and populate tables and reference them):

ActiveRecord::Schema.define do
  create_table :things do |t|
    t.integer :id, :null => false
    t.string  :name

class Thing < ActiveRecord::Base

  id:   0,
  name: 'Broomstick'

Care about the Environment

The other magic in Rails is the environment selection. The main benefit with this is that we can have isolated connection configurations and have our Ruby app automatically select the correct settings for us (using our environment variable ENV).

require 'active_record'

conf = case ENV['DB']
when 'conf1'
  adapter: 'sqlite3',
  database: 'db/mydb1.sqlite3'
when 'conf2'
  adapter: 'sqlite3',
  database: 'db/mydb2.sqlite3'
  raise 'export DB=conf[n]'

ActiveRecord::Base.establish_connection conf

Mind you, before this will work you first need to set the environment variable:

export DB=conf1 # or conf2

Now, depending on ENV[‘DB’], the code will open a connection to the corresponding database.

Best Practises

It’s never a good idea to store sensitive information (like database connection information and usernames and password of any kind) in your code base. Rails uses an external database configuration file called database.yml to solve this problem, so lets implement one ourselves.


  adapter: sqlite3
  database: db/mydb1.sqlite3

  adapter: sqlite3
  database: db/mydb2.sqlite3

Loading this YAML file is very simple:

require 'active_record'
conf = YAML.load_file('database.yml')
ActiveRecord::Base.establish_connection conf[ENV['DB']]

Now we can set our environment variable same as before, but our code will look in a YAML file for the proper database configuration automatically, without having to store database connection information directly inside our code.

Association Cardinality in Rails

From time to time I’ve noticed people who struggle with cardinality and associations in Ruby on Rails. So, I thought I would attempt to create a cheat sheet here to help developers understand relationship cardinality and how it maps to associations.

ActiveRecord can be used to describe relations with one-to-one, one-to-many and many-to-many cardinality; where each model defines its relation to another. Let’s cover each of the three types of associations.


Use `has_one` in the base and `belongs_to` in the association:

class Family < ActiveRecord::Base
  has_one :home
class Home < ActiveRecord::Base
  belongs_to :family

A common question about a one-to-one association is ‘how to know which direction the has_one and belongs_to go?’  The correct way to know, is that whichever model has the foreign key, gets the `belongs_to`.  In this case, Home has the foreign key `family_id`.

One-to-one relationships are a bit odd, and as a general rule, if you find yourself using a lot of them, there is probably a better solution.


Use `has_many` in the base and `belongs_to` in the association:

class Family < ActiveRecord::Base
  has_many :parents
class Parent < ActiveRecord::Base
  belongs_to :family

This will be your most common relationship. As with one-to-one’s, the table with the foreign key gets the `belongs_to` (although this is a lot more obvious with a one-to-many). In this case the foreign key is `family_id`.


These can be a lot more complicated and there is actually a couple of different ways to do it.

The first way involves a specific joining model. This results in 2 stages of has_many associations. It is referred to as `has_many :through` and is primarily used if you need to fully control the joining model/table:

class Family < ActiveRecord::Base
  belongs_to :parent
  belongs_to :kid
class Parent < ActiveRecord::Base
  has_many :kids, through: :families
class Kid < ActiveRecord::Base
  has_many :parents, through: :families

The second (and my preferred way) is to use the `has_and_belongs_to_many` method:

class Parent < ActiveRecord::Base
  has_and_belongs_to_many :kids 
class Kid < ActiveRecord::Base
  has_and_belongs_to_many :parents

The main difference (or disadvantage) with the `has_and_belongs_to_many`method is that the intermediary joining table and foreign keys need to be exactly named to match what Rails expects. Which many-to-many method you use ultimately depends on whether you need to work with the relationship model as its own entity directly.

MySQL utf8mb4 Encoding Breaks ActiveRecord’s Schema Setup

I recently wrote about the virtues of true UTF8 (utf8mb4) character sets in MySQL and how to change your database to use it. Today we will discuss a possible problem you may encounter when you do when programming on Ruby on Rails. The error looks something like this:

$ rake db:setup

Mysql::Error: Specified key was too long; max key length is 767 bytes:
CREATE UNIQUE INDEX unique_schema_migrations ON schema_migrations (version)

The problem exists because the utf8mb4 character set uses the full 4 bytes per character rather than the 1-3 of UTF8 (the character set most people mistakenly use thinking they’ll have full Unicode compliance). Because of this extra size, the schema_migration may no longer fit.

This small patch will set default mysql string column length to 191 instead of 255 which is the new index limit on utf8mb4 (aka real utf8).

# config/initializers/mysqlpls.rb
require 'active_record/connection_adapters/abstract_mysql_adapter'

module ActiveRecord
  module ConnectionAdapters
    class AbstractMysqlAdapter
      NATIVE_DATABASE_TYPES[:string] = { :name => "varchar", :limit => 191 }


MySQL’s UTF8 isn’t *really* UTF8 (and how to properly support Unicode)

I was forced to pull out my hair recently, after several SQL queries with UTF8 uni-coded text being fired from my project of the day, were failing to insert into my UTF8 MySQL database. Working on a project with a lot of middle eastern and asian content was simply crashing out my SQL insert queries and I was loosing a tremendous quantity of data.

Turns out MySQL’s UTF8 character set only partially implements proper UTF-8 encoding. It can only store UTF-8-encoded symbols that consist of one to three bytes; encoded symbols that take up four bytes aren’t supported. Luckily, MySQL 5.5.3 introduced a new encoding called utf8mb4 which maps to proper UTF-8 and thus fully supports Unicode, including astral symbols.

Switching from MySQL’s utf8 to utf8mb4

First, we need to change the character set and collation properties of the database, tables, and columns, to use utf8mb4, instead of utf8.

# For each database:
ALTER DATABASE database_name CHARACTER SET = utf8mb4 COLLATE utf8mb4_unicode_ci;
# For each table:
ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
# For each column:
ALTER TABLE table_name CHANGE column_name column_name VARCHAR(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

Note: Don’t simply copy-paste this! You will need to tailor the queries to meet your specific requirements, the above lines are for illustrative purposes only.

Repair and optimize all tables:

Do this with some simple SQL Queries:

# For each table
REPAIR TABLE table_name;
OPTIMIZE TABLE table_name;

Or using the MySQL command-line:

$ mysqlcheck -u root -p --auto-repair --optimize --all-databases

Note: Don’t forget to change the character encoding for your PHP/Ruby code to use the correct character encoding – i.e. utf8mb4 instead of utf8.

Test the changes:

You can test that the changes have taken effect by running this command to see if the collation/charsets have been switched to utf8mb4:

SHOW VARIABLES WHERE Variable_name LIKE ’character\_set\_%’ OR Variable_name LIKE ’collation%’;

Alternatively, change the default character set in MySQL.

In the /etc/my.cnf config file, we set the following instructions:

default-character-set = utf8mb4

default-character-set = utf8mb4

collation-server = utf8mb4_unicode_ci
init-connect='SET NAMES utf8mb4'
character-set-server = utf8mb4

That’s it. Obviously you will need to restart my SQL first though, and it will only apply to databases made after the default change, but I highly recommend this change. Even if you think you don’t need the full range of UTF8 characters, it only takes one to mess things up!


Never use utf8 in MySQL — always use utf8mb4 instead. Arbitrarily limiting the set of symbols you can use is just silly and is bound to cause a problem if your user is a young Japanese girl putting lots of cats in your strings. Why would you risk loosing lose data every time an Arabian user writes a message in their native locale. There’s no logical reason for it, and a few minutes of pain now, might save you a lot of heartache later. Do the right thing, and use utf8mb4 instead.

Using Ruby’s Metaprogramming to Initialize an Object From a Hash

Consider the code:

class A
  attr_accessor :b, :c, :d, :e, :h, :i, :x

Now imagine that you want to initialize each instance variable to the one that has the same name in the hash.. Imagine all the repetitive and crappy code that would generate.

But this is Ruby and with Ruby there is *nearly* always a better way.  Instead, meta-program it, and mix-it-in.

module constructed_from_hash
 def initialize(h)
  h.each { |k, v| send("#{k}=", v) }

class A
 include constructed_from_hash
 attr_accessor :b, :c, :d, :e, :h, :i, :x

Nice, elegant and clean. Just the way Ruby code is supposed to be. AND this code will now scale, as more accessors are added to the object over time, the constructor too, wont need reprogramming. If you don’t need to do this often, you can pull just the constructor out of the module and put it directly into the class, but this way provides the most flexibility.

Header image taken from Examining Dwemthy’s Array composite pattern. An interesting read in it’s own right. check it out.

‘belongs_to’ and ‘has_one’ Differentiated

One of the more common confusions with ActiveRecord associations is the difference between the `has_one` and `belongs_to` relationships.

However, they are not interchangeable, and there are some serious differences. A `belongs_to` can only go in the class that holds the foreign key whereas `has_one` means that there is a foreign key in another table that references this class. So `has_one` can only go in a class that is referenced by a column in another table.

So this is wrong:

class Transaction < ActiveRecord::Base
  # The transactions table has a order_id  
  has_one :order                

class Order < ActiveRecord::Base
  # The orders table has a transaction_id
  has_one :transaction          

So is this:

class Transaction < ActiveRecord::Base
  # The transactions table has a order_id
  belongs_to :order             

class Order < ActiveRecord::Base
  # The orders table has a transaction_id
  belongs_to :transaction     

For a two-way association, you need one of each, and they have to go in the right class. Even for a one-way association, it matters which one you use, and which direction you use it:

class Transaction < ActiveRecord::Base
  # This table has no foreign keys
  has_one :order             

class Order < ActiveRecord::Base
  # The orders table has a transaction_id
  belongs_to :transaction     

System-wide Git Global Ignores

If you are like me and love using a Mac for your development tasks, and want a way to get Git to ignore any file (like those pesky .ds_store’s) forever and for EVERY repository there is a very simple way to it.

Open Terminal and type:

git config --global core.excludesfile ~/.gitignore

and then:

echo .DS_Store >> ~/.gitignore

This will work for anything you want, just modify the second command as appropriate.  And you can run the second command as many times as you need.

Ruby Script to Import Google Contact Photos From Gravatar

Google Contact photos are a much neglected feature of the Google Stack. It really adds to the user experience when you see each of your contact photos when you make or receive a call. However, it can be a real pain (especially if you have hundreds of contacts).

But I had an idea recently, to try and match my Google Contact emails with Gravatar and try to auto-populate some of the dozens of contacts that didn’t already have a photo (after all a Gravatar is better than nothing).

So I wrote a Ruby script to find my contacts missing a photo and try to update it with a Gravatar (wherever possible). NB: You may need to first install the GData (Google Data) gem by opening a Terminal window and issuing: sudo gem install gdata.

#!/usr/bin/env ruby

# Google Contact Photos - Gravatar Importer
# Written by Ashley Angell
# Licenced under Creative Commons with Attribution

require "rubygems"
require "gdata"
require "rexml/document"
require "digest/md5"
require "net/http"
include REXML

none = 'd5fe5cbcc31cff5f8ac010db72eb000c'
user = ARGV[0]
pass = ARGV[1]

client =
client.clientlogin(user, pass)
data = client.get("{user}/full?max-results=10000")
myxml = data.body
p "contacts"
puts "-"*70
i = 0
myxml.each_element("feed/entry") do |e|
    gd = e.elements['gd:email']
    if !gd.nil?
      email = gd.attributes['address'].downcase
      hash = Digest::MD5.hexdigest(email)
      image_src = "{hash}"
      nil_image = false
      image_element = e.get_elements("link[@rel='']")[0]
      if !image_element.nil? and image_element.attributes['gd:etag'].nil?
        data = nil
        md5 = nil
        Net::HTTP.start(URI.parse(image_src).host) do |http|
          resp = http.get(URI.parse(image_src).path)
          data = resp.body
          md5 = Digest::MD5.hexdigest(data)
"#{email}.png", 'w') do |f|
            f.puts data if md5 != none
        md5 = Digest::MD5.hexdigest(data)
        if md5 != none
          puts "#{email} > #{image_src}"
          client.put_file(image_element.attributes['href'], "#{email}.png", 'image/png')
          i = i + 1
          puts "#{email} > no match"
        puts "#{email} > skipped (already has photo)"
      File.delete("#{email}.png") if File.exists?("#{email}.png")
  rescue Exception => ex
    puts ex
puts "Updated #{i} contact photos"

To execute it, simply copy and paste this into a text editor (or download it and unzip) and from Terminal (command) window and execute the following commands:

sudo chmod +x googlegravatarimporter.rb [Enter]
./googlegravatarer.rb your_password [Enter]

It will cycle through your Google Contacts and indicate what action was taken. For me, surprisingly updated a few dozen contacts (even more than I expected).

I’ve posted this here for others that might want to do the same thing but cannot be bothered writing the script for it. Consider it posted here under Creative Commons with Attribution.

Adding Wiki Style Functionality to Your Rails Site Using 'acts_as_versioned'

If you need to add basic wiki style functionality to your Ruby on Rails models, there is a really easy way to get similar model versioning without having to resort to cutting the code yourself.

The acts_as_versioned ‘plugin’ has been available for quite some time, but its been made far better by it now becoming a gem instead of an old-school plugin. The authors have gone to considerable effort to make it as painless as possible to use.

This post, is designed to give you a brief over-view into how to get up and running with with models which ‘acts_as_versioned’.  Because its the current version (at time of posting) and because its awesome, this walk-though assumes that you are using Rails 3, not 2.  The instructions for Rails 2 sites are similar, but you’ll need to tweak this for it to work.

First, you need to grab the gem:

sudo gem install acts_as_versioned

Next, add the dependency to the ‘Gemfile’, it doesn’t matter too much where it goes, I stuck it somewhere in the middle:

gem 'acts_as_versioned', '0.6.0'

Next, just under the ‘ActiveRecord::Base’ line in the model’s class file, instruct the class that its to act as a versioned model.

class Article < ActiveRecord::Base

Then, in the migration file you need to execute the model's method to create the version table.  This is key because the acts_as_versioned gem actually creates an additional database table to house all the previous versions of a given record.  Obviously, you need to delete the table is the schema is taken down.  My migration now looks like:

class CreateArticles < ActiveRecord::Migration
  def self.up
    create_table :article do |t|
      t.string :title
      t.string :body
      t.integer :user_id


  def self.down
    drop_table :articles

The key method is the


which creates the version table of the model. Now, get rake to create the database:

 rake db:migrate

Thats it!  Its done.  Using acts_as_versioned is simple. I'll provide some examples, where '@article' represents an instance of a model setup 'acts_as_versioned'. To find the current version of an article you can use the version property:


But just performing a normal ActiveRecord lookup returns the most current version anyway, so to revert to a previous version use the revert_to method on an article instance:


You can save (just like you've done a hundred times before) a previous version as the current on by using the save method. The save on a reverted articles will just create a new version.

To get the number of versions:


Since '@article.versions' returns an array of versions, you can do neat things like this:


<% for version in @article.versions.reverse %> Version <%= version.version %> <%= link_to '(revert to this version)', :action => 'revert_to_version', :version =>, :id => @article %>
<% end %>

Obviously for this to work, you'd need to create a 'revert_to_version' action in the appropriate controller, but you get the idea.

acts_as_versioned is an amazing piece of work, and aside from the wiki-like functionality it gives you for very little effort, I can imagine scenarios such as audit and trace logs and "undo" features which could really benefit from this little gem.