IDisposable StopWatch to Benchmark code blocks (via Lambda or Delegate) in C#

Sometimes you need to time code execution for use *inside* your application. the StopWatch class was designed just for this purpose, but you end up with some pretty ugly code that looks like this:

Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
// Do something.
for (int i = 0; i < 1000; i++) { Thread.Sleep(1); }
// Stop timing.
stopwatch.Stop();
// Write result.
Console.WriteLine("Time elapsed: {0}", stopwatch.Elapsed);

This gets really messy, especially if the code is already pretty complicated. But with very little effort you can make the .Net StopWatch just as beautiful as the Benchmark class in Ruby.

public class DisposableStopwatch: IDisposable {
  private readonly Stopwatch sw;
  private readonly Action f;

  public DisposableStopwatch(Action f) {
    this.f = f;
    sw = Stopwatch.StartNew();
  }

  public void Dispose() {
    sw.Stop();
    f(sw.Elapsed);
  }

}

To use the new stopwatch:

using (new DisposableStopwatch(t => Console.WriteLine("{0} elapsed", t)) {
  // do stuff that I want to measure
}

This is the best solution I’ve ever seen for this problem! No extension (so that it can be used on many classes) and very clean and very simple!

How to Clone or Duplicate a PostgreSQL Database

Sometimes you may find yourself needing to duplicate a postgres database – complete with schema, data; exactly. Sometimes I need to do this because I want to try out some ideas on an existing database but without the hassle of having to backup and restore or write rollbacks for the changes I want to make.

Luckily, it’s super easy to do this.  First ensure that there are not active connections to the source database; and then open the SQL Terminal of your choice and execute:

CREATE DATABASE newdb WITH TEMPLATE originaldb OWNER dbuser;

This will create a new database, by using the source database as a template.

If you get the message: “ERROR: Database being accessed by other users.” don’t worry; it just means that there are still open database connections, and these will need to be closed before it will work.

97 Things Every Programmer Should Know

PLEASE NOTE: This is a copy of the official list and I only copy it here for my own personal purposes (in case the list is lost), and not because I am trying to circumvent copyright or profiteer from it.

  1. Act with Prudence by Seb Rose
  2. Apply Functional Programming Principles by Edward Garson
  3. Ask “What Would the User Do?” (You Are not the User) by Giles Colborne
  4. Automate Your Coding Standard by Filip van Laenen
  5. Beauty Is in Simplicity by Jørn Ølmheim
  6. Before You Refactor by Rajith Attapattu
  7. Beware the Share by Udi Dahan
  8. The Boy Scout Rule by Uncle Bob
  9. Check Your Code First before Looking to Blame Others by Allan Kelly
  10. Choose Your Tools with Care by Giovanni Asproni
  11. Code in the Language of the Domain by Dan North
  12. Code Is Design by Ryan Brush
  13. Code Layout Matters by Steve Freeman
  14. Code Reviews by Mattias Karlsson
  15. Coding with Reason by Yechiel Kimchi
  16. A Comment on Comments by Cal Evans
  17. Comment Only What the Code Cannot Say by Kevlin Henney
  18. Continuous Learning by Clint Shank
  19. Convenience Is not an -ility by Gregor Hohpe
  20. Deploy Early and Often by Steve Berczuk
  21. Distinguish Business Exceptions from Technical by Dan Bergh Johnsson
  22. Do Lots of Deliberate Practice by Jon Jagger
  23. Domain-Specific Languages by Michael Hunger
  24. Don’t Be Afraid to Break Things by Mike Lewis
  25. Don’t Be Cute with Your Test Data by Rod Begbie
  26. Don’t Ignore that Error! by Pete Goodliffe
  27. Don’t Just Learn the Language, Understand its Culture by Anders Norås
  28. Don’t Nail Your Program into the Upright Position by Verity Stob
  29. Don’t Rely on “Magic Happens Here” by AlanGriffiths
  30. Don’t Repeat Yourself by Steve Smith
  31. Don’t Touch that Code! by Cal Evans
  32. Encapsulate Behavior, not Just State by Einar Landre
  33. Floating-point Numbers Aren’t Real by Chuck Allison
  34. Fulfill Your Ambitions with Open Source by Richard Monson-Haefel
  35. The Golden Rule of API Design by Michael Feathers
  36. The Guru Myth by Ryan Brush
  37. Hard Work Does not Pay Off by Olve Maudal
  38. How to Use a Bug Tracker by Matt Doar
  39. Improve Code by Removing It by Pete Goodliffe
  40. Install Me by Marcus Baker
  41. Inter-Process Communication Affects Application Response Time by Randy Stafford
  42. Keep the Build Clean by Johannes Brodwall
  43. Know How to Use Command-line Tools by Carroll Robinson
  44. Know Well More than Two Programming Languages by Russel Winder
  45. Know Your IDE by Heinz Kabutz
  46. Know Your Limits by Greg Colvin
  47. Know Your Next Commit by Dan Bergh Johnsson
  48. Large Interconnected Data Belongs to a Database by Diomidis Spinellis
  49. Learn Foreign Languages by Klaus Marquardt
  50. Learn to Estimate by Giovanni Asproni
  51. Learn to Say “Hello, World” by Thomas Guest
  52. Let Your Project Speak for Itself by Daniel Lindner
  53. The Linker Is not a Magical Program by Walter Bright
  54. The Longevity of Interim Solutions by Klaus Marquardt
  55. Make Interfaces Easy to Use Correctly and Hard to Use Incorrectly by Scott Meyers
  56. Make the Invisible More Visible by Jon Jagger
  57. Message Passing Leads to Better Scalability in Parallel Systems by Russel Winder
  58. A Message to the Future by Linda Rising
  59. Missing Opportunities for Polymorphism by Kirk Pepperdine
  60. News of the Weird: Testers Are Your Friends by Burk Hufnagel
  61. One Binary by Steve Freeman
  62. Only the Code Tells the Truth by Peter Sommerlad
  63. Own (and Refactor) the Build by Steve Berczuk
  64. Pair Program and Feel the Flow by Gudny Hauknes, Ann Katrin Gagnat, and Kari Røssland
  65. Prefer Domain-Specific Types to Primitive Types by Einar Landre
  66. Prevent Errors by Giles Colborne
  67. The Professional Programmer by Uncle Bob
  68. Put Everything Under Version Control by Diomidis Spinellis
  69. Put the Mouse Down and Step Away from the Keyboard by Burk Hufnagel
  70. Read Code by Karianne Berg
  71. Read the Humanities by Keith Braithwaite
  72. Reinvent the Wheel Often by Jason P Sage
  73. Resist the Temptation of the Singleton Pattern by Sam Saariste
  74. The Road to Performance Is Littered with Dirty Code Bombs by Kirk Pepperdine
  75. Simplicity Comes from Reduction by Paul W. Homer
  76. The Single Responsibility Principle by Uncle Bob
  77. Start from Yes by Alex Miller
  78. Step Back and Automate, Automate, Automate by Cay Horstmann
  79. Take Advantage of Code Analysis Tools by Sarah Mount
  80. Test for Required Behavior, not Incidental Behavior by Kevlin Henney
  81. Test Precisely and Concretely by Kevlin Henney
  82. Test While You Sleep (and over Weekends) by Rajith Attapattu
  83. Testing Is the Engineering Rigor of Software Development by Neal Ford
  84. Thinking in States by Niclas Nilsson
  85. Two Heads Are Often Better than One by Adrian Wible
  86. Two Wrongs Can Make a Right (and Are Difficult to Fix) by Allan Kelly
  87. Ubuntu Coding for Your Friends by Aslam Khan
  88. The Unix Tools Are Your Friends by Diomidis Spinellis
  89. Use the Right Algorithm and Data Structure by JC van Winkel
  90. Verbose Logging Will Disturb Your Sleep by Johannes Brodwall
  91. WET Dilutes Performance Bottlenecks by Kirk Pepperdine
  92. When Programmers and Testers Collaborate by Janet Gregory
  93. Write Code as If You Had to Support It for the Rest of Your Life by Yuriy Zubarev
  94. Write Small Functions Using Examples by Keith Braithwaite
  95. Write Tests for People by Gerard Meszaros
  96. You Gotta Care about the Code by Pete Goodliffe
  97. Your Customers Do not Mean What They Say by Nate Jackson

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/libv8-3.16.14.3 for inspection.
Results logged to /Users/ash/.rvm/gems/ruby-2.2.1/extensions/x86_64-darwin-14/2.2.0-static/libv8-3.16.14.3/gem_make.out

An error occurred while installing libv8 (3.16.14.3), and Bundler cannot continue.
Make sure that `gem install libv8 -v '3.16.14.3'` 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 '3.16.14.3' -- --with-system-v8

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.

One-to-one

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

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

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.

One-to-many

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

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

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`.

Many-to-many

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
end
class Parent < ActiveRecord::Base
  has_many :kids, through: :families
end
class Kid < ActiveRecord::Base
  has_many :parents, through: :families
end

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 
end
class Kid < ActiveRecord::Base
  has_and_belongs_to_many :parents
end

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 }
    end
  end
end

 

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
end

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) }
 end
end

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

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                
end

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

So is this:

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

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

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             
end

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

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
# http://ashleyangell.com
# 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 = GData::Client::Contacts.new
client.clientlogin(user, pass)
data = client.get("https://www.google.com/m8/feeds/contacts/#{user}/full?max-results=10000")
myxml = Document.new data.body
p "contacts"
puts "-"*70
i = 0
myxml.each_element("feed/entry") do |e|
  begin
    gd = e.elements['gd:email']
    if !gd.nil?
      email = gd.attributes['address'].downcase
      hash = Digest::MD5.hexdigest(email)
      image_src = "http://www.gravatar.com/avatar/#{hash}"
      nil_image = false
      image_element = e.get_elements("link[@rel='http://schemas.google.com/contacts/2008/rel#photo']")[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)
          File.open("#{email}.png", 'w') do |f|
            f.puts data if md5 != none
          end
        end
        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
        else
          puts "#{email} > no match"
        end
      else
        puts "#{email} > skipped (already has photo)"
      end
      File.delete("#{email}.png") if File.exists?("#{email}.png")
    end
  rescue Exception => ex
    puts ex
  end
end
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.address@gmail.com 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.

‘File not found: lib’ Error installing Rails Gem

I recently had a problem trying to install Rails 3 on my MacBook with a fresh OSX Snow Leopard:

sudo gem install rails
Password: {entered}
Successfully installed rails-3.0.7
1 gem installed
Installing ri documentation for rails-3.0.7...
File not found: lib

Turns out this is a somewhat common problem.  But it seems that the solution is easy, just manually reinstall RDoc. To do this run these 3 commands:

sudo gem install rdoc-data
sudo rdoc-data --install
sudo gem rdoc --all --overwrite

The last line in particular will re-generate all the documentation for your installed gems (including Rails) and can take a while, but you should be able to confirm the fix by reissuing the Rails gem install command:

sudo gem install rails

shows that rails now installs properly and says that it has installed both ri and RDoc documentation without issue.