bakineggs

Blog

• October 16, 2012 @ 5:58am

  Useful Bug Reports

  All useful bug reports contain the following pieces of information:

  1. What actions did you take?
  2. What happened as a result?
  3. What should have happened instead?

  Without these pieces of information, a bug report is useless.

• October 3, 2012 @ 11:34am

  Ensuring schema.rb is Up to Date

  Sometimes on a large shared Rails project, people forget to commit the changes to db/schema.rb when they add migrations. To resolve this, I made the migration rake task to append a checksum of the migrations to db/schema.rb and wrote a spec to ensure that the checksum is up to date. If someone forgets to commit a db/schema.rb change, our continuous integration tests fail and they commit the db/schema.rb change.

  lib/tasks/migrate.rake

  namespace :db do
    task :migrate do
      checksum = Digest::MD5.hexdigest Dir.glob('db/migrate/*').sort.map {|path| File.read path}.join "\n"
      `echo '# Checksum: #{checksum}' >> db/schema.rb`
    end
  end
  

  database_schema_spec.rb

  describe 'db/schema.rb' do
    it 'includes the changes from all migrations' do
      if checksum_line = File.read('db/schema.rb').split("\n").detect {|line| line.match /^# Checksum: w+$/}
        checksum = checksum_line.match(/^# Checksum: (w+)$/)[1]
        checksum.should == Digest::MD5.hexdigest(Dir.glob('db/migrate/*').sort.map {|path| File.read path}.join "\n")
      else
        fail 'db/schema.rb does not contain a migration directory checksum! Please run rake db:migrate'
      end
    end
  end
  

• October 14, 2011 @ 2:58am

  Default Values for Associations in Rails

  Sometimes in a Rails app, you'd like to have a default value for an association. Consider the following example from a Stack Overflow question:

  class User < ActiveRecord::Base
    has_one :profile
  end
  
  class Profile < ActiveRecord::Base
    belongs_to :user
  end
  
  user = User.new
  user.profile.something #=> ERROR
  

  Rails doesn't provide a built-in way to specify a default value, but we can do it ourselves:

  class User < ActiveRecord::Base
    has_one :profile
  
    def profile_with_default
      profile_without_default || build_profile
    end
    alias_method_chain :profile, :default
  end
  
  class Profile < ActiveRecord::Base
    belongs_to :user
  end
  
  user = User.new
  user.profile.something #=> builds a profile for you
  

• February 9, 2011 @ 6:50am

  Filter in the Database, not the Application

  Code smells are patterns in code that can indicate possible problem areas. One code smell is loading many records out of a database when you only want some of them and doing filtering in the application logic.

  The other day, I sniffed out this smell in our suggested users feature. We assign each suggested user a weight that determines their probability of being suggested. A user with a weight that is double another user's has double the odds of being suggested.

  To determine what users to suggest, we were loading all suggested users out of the database and using an algorithm that repeatedly picked users based on a weighted probability until it had the desired amount.

  Continued...

• May 1, 2010 @ 11:48pm

  Testing AJAX with Cucumber and Capybara

  For a recent project, I used Cucumber and Capybara for my user stories. When I decided to AJAXify the functionality, I wrote some stories tagged with @javascript that were nearly identical to my non-javascript versions (non-JS and JS). Since the changes to the page content should be the same with or without Javascript, testing the page content wouldn't actually verify that the AJAX funtionality was working. To solve this, I created the step "Then the page should not change" with the following definition:

  Then 'the page should not change again' do
    evaluate_script('window.onunload = window.stop')
  end
  

  Now, if the user clicks a link that doesn't have its behavior overwritten by Javascript, a blank page will be displayed and any following steps will fail.

• January 29, 2010 @ 7:47am

  Early Returns for Clarity's Sake

  I don't like to nitpick about programming style, but there is one thing that always bugs me. I frequently come across functions structured as follows:

  function foo() {
    if (a) {
      // do stuff
    } else {
      return false;
    }
  }
  

  I always wonder why the programmer didn't use an early return:

  function foo() {
    if (!a)
      return false;
  
    // do stuff
  }
  

  Continued...

• October 28, 2009 @ 5:41pm

  Analogy for Net Neutrality

  ISPs are like UPS or Fedex to the web. They deliver packets from sender to receiver.

  With net neutrality, they must place equal priority on each delivery and deliver the packets untampered.

  Without, they may open, inspect, modify, delay, or even halt packets of their choice.

• May 25, 2009 @ 10:13am

  Using a Float Column in a Where Clause

  I spent about 12 hours today trying to figure out why one of my validates_uniqueness_of constraints was not working. Here's why:

  mysql> create table some_table (some_float_column float);
  Query OK, 0 rows affected (0.01 sec)
  
  mysql> insert into some_table (some_float_column) values (8.4537);
  Query OK, 1 row affected (0.00 sec)
  
  mysql> select * from some_table where some_float_column = 8.4537;
  Empty set (0.01 sec)

  Notice how I'd just inserted a row with that value yet the row was not returned. All I had to do was change the float column to a decimal column.

• March 22, 2009 @ 6:22pm

  Auto-Start Juggernaut with Cucumber

  If you use Juggernaut and Cucumber, many of your features can fail unless you have a Juggernaut server running. You can add the following to your features/support/env.rb to automatically start and stop Juggernaut when you run your features:

  juggernaut = fork { exec 'juggernaut -c config/juggernaut.yml' }
  at_exit { exec 'kill', juggernaut.to_s }