Slash Dot Dash

Alistair Cockburn’s lightning talk on CQRS recorded at the Mountain West Ruby Conference 2010

Ben — Mon, 27 Sep 2010 21:57:43 +0000

Here’s Alistair Cockburn’s lightning talk on “Command Event DTO Architecture” recorded at the Mountain West Ruby Conference 2010 by confreaks.net. He talks about how his Hexagonal Architecture has been extended by Greg Young to form a Command-Event Architecture (aka CQRS).

This was originally posted as part of a 46 minute collection a talks, I’ve just extracted Alistair’s CQRS talk and made it available since the original location is no-longer providing video streaming.

There’s a reference library on Command-Query Responsibility Segregation if you’d like to know more. I’m posting this here as I’ve been working on a CQRS library in Ruby recently, with a Rails 3 plugin and small demo app which I’ll be linking to shortly.

Rails 3, RSpec and Cucumber setup

Ben — Mon, 27 Sep 2010 19:53:07 +0000

This quick how-to runs through creating a new Rails 3 application with both RSpec and Cucumber for testing (rather than Test::Unit).

Rails 3 requires (the somewhat confusingly versioned) RSpec 2 and rspec-rails. Similarly, Cucumber uses cucumber-rails for bootstrapping your Rails app and provides generators for creating features.

Install RSpec 2

sudo gem install rspec-rails --pre

Install Cucumber

sudo gem install cucumber-rails

Create a new Rails 3 application

Ensure you have the latest version of Rails 3 installed then create a new application, skipping creation of the test directory since we’ll be using RSpec and Cucumber (with spec and features) instead.

rails new  --skip-testunit

Add rspec-rails to the :test and :development groups to the Gemfile.

group :test, :development do
    gem 'rspec-rails', '>= 2.0.0.beta.22'
end

Add cucumber-rails and dependencies to the :cucumber group in the Gemfile:

group :cucumber do
    gem 'capybara'
    gem 'database_cleaner'
    gem 'cucumber-rails'
    gem 'cucumber'
    gem 'spork'
    gem 'launchy'
end

Ensure all gems are installed by using Bundler:

sudo bundle install

Then install the RSpec extensions (creates the spec directory and creates a rake task):

rails generate rspec:install

Now we can specify that Rails itself uses RSpec when running generators by adding the following inside config/applicaton.rb:

config.generators do |g|
  g.test_framework :rspec
end

Next, bootstrap your Rails app, for Cucumber:

rails generate cucumber:install --rspec --capybara

That’s it! Now the following rake tasks exist to execute your specs or cucumber features (by default rake will execute both).

rake spec
rake cucumber

Rails 3 scopes with chaining

Ben — Sat, 25 Sep 2010 12:33:30 +0000

Here’s a quick gotcha you should be aware of when using the fantastic new scope facility in Rails 3 (formerly named_scope).

Here’s a snippet that demonstrates how to chain scopes, allowing you to call Post.recent to get posts that have been published, ordered by date.

class Post < ActiveRecord::Base
  scope :published, lambda { where('published_at IS NOT NULL AND published_at <= ?', Time.zone.now) }
  scope :recent, published.order(:published_at)
end

However it contains a subtle bug; when chaining a lambda scope you must also wrap it with a lambda or else you will end up with the wrong result. The correct example is as follows.

class Post < ActiveRecord::Base
  scope :published, lambda { where('published_at IS NOT NULL AND published_at <= ?', Time.zone.now) }
  scope :recent, lambda { published.order(:published_at) }
end

José Valim explains the reason in the Rails ticket #4960.

class Auction < ActiveRecord::Base
  scope :started, lambda { where("starting_at <= ?", Time.now) }
  scope :unfinished, lambda { where("ending_at > ?", Time.now) }
  scope :active, started.unfinished
end
You can chain scopes, but they will be evaluated at the moment you call them.
That said, when you call started, it will execute the lambda, so it will have a frozen Time.now. In other words, chaining lambda scopes will likely give you the wrong result.
You need to wrap the scope :active in a lambda as well.
scope :active, lambda { started.unfinished }

Ruby and Rails Magazines available to Buy or download

Ben — Wed, 18 Mar 2009 22:03:19 +0000

The thriving Ruby and Rails communities have produced a couple of magazines that you can buy (to show your support) or download PDF versions absolutely free.

Rails Magazine – Issue 1 (1st March 2009)

The Beginning; 36 pages of Rails goodness.

Receiving E-Mail With Rails by Jason Seifer
Delegation in Ruby by Khaled al Habache
Subscription billing with Saasy by Alex MacCaw
Making the Switch From RSpec to Shoulda by Dan Pickett
Playing Hooky a.k.a. web hooks by John Nunemaker
Adhearsion by Jason Goecke & Jay Phillips
Rails Performance Analysis by Terry Heath
Getting Started with JRuby and JRuby on Rails by Joshua Moore
Extending Rails Through Plugins by John Yerhot

Buy Now or Download for free.

The Rubyist – Issue 1 (August 2008)

Hampton Catlin, Rein Henrichs, and friends in the first issue of the Rubyist. INSIDE: An interview with Rein Henrichs on Ruby best practices, an interview with Hampton Catlin about Jabl, columns from Giles Bowkett and Rein Henrichs, a Ruby quiz-esque challenge (you can win an iPhone! Yes, you!), building DataMapper adapters, Ben Scofield shares some techniques for auditing your code, using RubyOSA with Evan Light, Yehuda Katz waxes rhapsodic on performance measures in Merb, and learning about building gems with BDD from Jamie van Dyke!

Buy Now or Download for free.

The Rubyist – Issue 2 (February 2009)

Regional conferences with Pat Eyler
Talking about the Rails merge with Zach Inglis, and interviews with DHH, Ted Han, and more
Scott Chacon drops some Git knowledge
Yehuda Katz discusses his journey from Rails to Merb to Rails
Martin Rehfeld shares his solution from last issue’s homework
Obie Fernandez talks about client managment
Aaron Quint spends some time with Sinatra
Evan David Light talks BDD
Ben Scofield talks about testing iPhone applications using Ruby
Eric Hodel talks about the next generation of RubyGems
Dennis Theisen teaches how to use ActiveMerchant
Carlo Pecchia shows off JRuby

Buy Now or Download for free.

Migrating this blog from Typo to WordPress

Ben — Fri, 02 Jan 2009 14:50:39 +0000

After recently installing Phusion Passenger under Apache 2 to host my Rails apps I wanted to give Ruby Enterprise Edition a go. However as I was running an old version of Typo (version 4.x) which didn’t seem to like running under REE I decided to migrate to WordPress; upgrading Typo would be just as much work.

There’s already a Ruby upgrade script to create a WordPress compatible WXR file for importing which includes all posts, comments and categories from Typo. I needed to modify the Ruby script slightly to get working with the version of Typo I had installed.

Exporting Typo blog content to WordPress WXR

The Ruby script needs to be placed into the script directory of the Typo application root and then run under the production Rails environment:

RAILS_ENV=production ruby script/wp_export.rb > blog.wxr

Installing WordPress

Simply follow the basic WordPress install guide after downloading the latest software (version 2.7 at the time of writing). The pre-requisites for WordPress are PHP 4.3 or newer and MySQL 4.0 or greater.

Import existing content

Once WordPress is installed, log in to the admin section and select Import from the Tools menu. Choose the WordPress option from the list (Import posts, pages, comments, custom fields, categories, and tags from a WordPress export file). You’ll need to select the blog.wxr file created by the Ruby script and then click Upload file and import. That should recreate your existing Typo blog content (and comments), you may be asked to map the Typo user(s) to WordPress accounts.

With the content installed, the final change required is to setup the Permalink Settings from Settings > Permalinks. Select the Day and name option (giving URLs such as http://www.slashdotdash.net/2009/01/02/sample-post/). You may need to manually edit or create the .htaccess file to get the rewrite rules working.

# .htaccess

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

With this working you should find that the standard Typo permalinks (such as http://www.slashdotdash.net/articles/2009/01/02/sample-post/) will now redirect to the corresponding WordPress blog entry, ensuring no broken links when switching from Typo to WordPress.

Known Issues

You’ll probably have a problem with RSS feed readers creating duplicates of the last 10 posts (depending upon your “Syndication feeds show the most recent” settings) since the post URLs and GUIDs will have changed.

Easy Merb installation using Thor

Ben — Sat, 20 Sep 2008 00:42:00 +0000

There’s now a much simpler way to get Merb setup than I previously noted. By using Thor, either the Stable (Gem) or Edge releases of Merb can be installed as a local Ruby Gem or bundled with your Merb app.

The thor tasks are context aware. Run them in a Merb application directory and they’ll bundle the relevant files with your app; keeping dependencies with the application and making it independent of your system’s Ruby Gems. When run outside any application, they target the system in general (installing as a standard Gem). This is determined by the presence of a local gems directory (or by specifying the --merb-root option).

Installing Edge Merb and DataMapper

mkdir merb; cd merb
# Install Thor
sudo gem install thor
# Get merb.thor file (or update existing file)
curl -L http://merbivore.com/merb.thor > merb.thor
thor merb:tasks:update
# Merb (edge)
sudo thor merb:edge:core --install
sudo thor merb:edge:more --install
sudo thor merb:edge:plugins --install
# DataMapper
sudo thor merb:edge:dm_core --install
sudo thor merb:edge:dm_more --install

Keeping updated with the latest Merb (merb-core and merb-more only) is now simply:

sudo thor merb:edge --install

Further details are given on the merbunity site.

Getting started with Merb and Datamapper

Ben — Sat, 05 Jul 2008 23:46:00 +0000

Merb is the up-and-coming Ruby web framework, designed to improve upon the ideas in Rails whilst being faster, lighter and less opinionated (or more agnostic). I wanted to discover whether it provides any benefits over Rails and what it does differently. The best way to find out; get it installed it and create a new app.

Update: There’s now a much easier way of getting Merb & DataMapper installed.

The official Merb website gives the following simple installation instructions.

sudo gem install merb

However, since I wanted to also try DataMapper as the ORM those instructions failed to install a working setup due to a conflict between Merb and DataMapper dependencies. Unperturbed, I finally got them both installed and working happily together by getting the bleeding edge code from each project’s github repository and following the instructions provided by Mathew Ford’s Living life on the edge. The book is also available on github, you can contribute patches there. Hopefully this issue will be resolved soon enough so that you’ll be able to install the official release gems for both Merb and DataMapper from Rubyforge (instead of running on edge).

Prerequisites

You must have git installed (sudo port install git-core using MacPorts on OS X).
Remove any older versions of merb (and datamapper) that you might have installed. Use gem list to view local gems and sudo gem uninstall to remove each individual gem.

The Easy Way

Matt’s book outlines an easy way of installing the latest merb & datamapper source, however it failed to properly install the DataMapper gem for me so I had to resort to the hardcore approach.

sudo gem install sake
sake -i 'http://edgy.4ninjas.org/edgy.sake'
sake edgy:install packages="merb-stack"

After installing, to keep up-to-date you just need to execute:

sake edgy:update

Now, if you’re hardcore…

Installing the required dependencies

Start by installing the gem dependancies.

sudo gem install rack mongrel json erubis mime-types rspec hpricot mocha rubigen haml markaby mailfactory ruby2ruby

Installing Merb

Download the merb source:

git clone git://github.com/wycats/merb-core.git
git clone git://github.com/wycats/merb-plugins.git
git clone git://github.com/wycats/merb-more.git

Then install the gems via rake:

cd merb-core ; rake install ; cd ..
cd merb-more ; rake install ; cd ..
cd merb-plugins; rake install ; cd ..

Installing DataMapper

git clone git://github.com/sam/extlib.git
git clone git://github.com/sam/do.git
cd extlib ; rake install ; cd ..
cd do
cd data_objects ; rake install ; cd ..
cd do_mysql ; rake install ; cd ..
cd ..
git clone git://github.com/sam/dm-core.git
git clone git://github.com/sam/dm-more.git
cd dm-core ; rake install ; cd ..
cd dm-more ; rake install ; cd ..

Keeping updated

To update your local gems with the latest code changes you’ll need to do a git pull and then rake install for each of the git repositories previously downloaded.

Creating your first Merb app

You create a new empty Merb app via the merb-gen utility.

merb-gen app demo

(You can also create flattened or single file applications if you wish).

merb-gen app app_name --flat      (for a flattened application)
merb-gen app app_name --very-flat (for a single file application)

As we’re using DataMapper we need to edit config/init.rb and uncomment the use_orm :datamapper line. The next step is to create the database settings file config/database.yml:

---
development: &defaults
  adapter:    mysql
  database:   demo_development
  username:   demo
  password:        p@ssword
  host:       localhost
test:
  <<:         *defaults
  database:   demo_test
production:
  <<:         *defaults
  database:   demo_production

You can now fire up the Merb server to make sure it runs.

$ merb
 ~ Loaded DEVELOPMENT Environment...
 ~ Connecting to database...
 ~ loading gem 'merb_datamapper' ...
 ~ Compiling routes...
 ~ Using 'share-nothing' cookie sessions (4kb limit per client)
 ~ Using Mongrel adapter

Some other useful commands to know:

merb -i                                                        # Interactive merb console
merb-gen model                             # Creates a Datamapper Model stub
merb-gen resource                     # Creates a full resource (incuding model, controller, views & test spec)
rake dm:db:automigrate            # Perform automigration
rake dm:db:autoupgrade            # Perform non destructive automigration

Let’s see how it goes from here with Merb!

Update: There’s now a much easier way of getting Merb & DataMapper installed.

Lifestreaming – combining your online activity into a single stream (using trawlr)

Ben — Wed, 12 Mar 2008 01:07:00 +0000

It’s been a year since I last mentioned trawlr on this blog at which point I promised no further status updates here. Well I’m going to just pretend I didn’t say that for now as I wanted to get some feedback (and usage) on the latest feature I’ve been working on.

Streaming your life away

It’s support for “lifestreaming” – combining your online identity from various different social sites into a single stream. Very much like a diary or timeline of events, grouped by date.

The inspiration for this feature came from a blog post by Jeremy Keith (hence the title) so props to him for the idea.

Lifestreaming is like Twitter, but covers everything you do online that is publicly available and has an RSS feed. Currently there’s support for Delicious, Flickr, Twitter, Upcoming, Last.fm, your own blog feed (RSS) and any other site that provides an RSS feed.

You can see an example of my lifestream in the screen shot. If you already have a trawlr.com account then why not give it a whirl and create your own lifestream. Don’t have an account yet? Registration is quick & simple (with no email activation required) and once you’ve tried out the lifestreaming, you might also be interested in the main RSS reader.

Once you’ve created your lifestream, it’ll be automatically updated throughout the day.

Let me know if you can think of any important sources I’ve missed, such as; YouTube, Picassa, SmugMug, FaceBook, MySpace, Google Reader shared items, Digg (dugg by) and Reddit (activity).

I’m planning to create a “widget” version of the lifestream so that it may be embedded within your own blog or website, allowing customisation of the display

Sphinx search with delta indexing thanks to Ultrasphinx

Ben — Sun, 09 Mar 2008 13:58:00 +0000

Evan Weaver has just announced delta indexing support for his UltraSphinx Rails plugin.

Delta indexing speeds up your updates by not reindexing the entire dataset every time.
First, in your .base file, set the indexer option delta to your maximum interval between full reindexes. A day or a week is good, depending. Add a little bit to account for the time it takes the actual index to run:
delta = <%= 1.day + 30.minutes %>
Now, configure your models for delta indexing in the is_indexed call:
is_indexed :fields => ['created_at', 'title', 'body'], :delta => true
Now you can run rake ultrasphinx:index:delta frequently, and only records that were changed within 1 day will be reindexed. You will need to run rake ultrasphinx:index:main once a day to move the delta contents into the main index.

From the UltraSphinx documentation.

I’ve previously written about how fast Sphinx search is in Rails searching with Sphinx using the acts_as_sphinx plugin (and also contributed a chapter to the Advanced Rails Recipes book using the UltraSphinx plugin). I’d now recommend using the UltraSphinx plugin if you want to take advantage of Sphinx for your Rails application.

In my opinion, this completes the ‘missing’ piece of functionality and should make Sphinx your default full-text search engine (if you’re using MySQL).

Pimp my MacBook Pro

Ben — Sat, 08 Mar 2008 20:19:00 +0000

Thanks to the increasing prevalence of Apple laptops – including the MacBook, MacBook Pro and new Air – having a Mac no longer makes you l33t! To combat this, a couple weeks ago I decided to pimp my MacBook Pro by changing the illuminated Apple logo on the case. A Canadian site sells a multitude of inserts that can be used to alter the logo.

Customize your laptop for only $4.99! These high-quality inserts will make your laptop one of a kind! Free Worldwide Shipping! Compatible with: iBooks, Powerbooks, MacBooks and MacBook Pros

The installation guide steps you through the process, the MacBook Pro is rated as “Medium” difficulty. Apart from the tight angle to unscrew the 2 retaining screws at the bottom of the screen, the tricky part to the process is removing the back of the screen using a credit card. You need a steady hand and a slightly cavalier attitude to prise the cover apart!

I went for the ‘Rainbow’ design – one of the original Apple logos – the end result is rather pleasant update to the plain white logo and it still glows in the dark.