Food for Thought

Installing rmagick on Windows

Adhiraj — Sun, 05 Jun 2011 08:00:46 +0000

Prerequisites:
Ruby > 1.8.6
DevKit (any version)
No other ImageMagick installation or PATH entry

Step 1:
Installing ImageMagick:

Download ImageMagick:
http://www.imagemagick.org/download/binaries/ImageMagick-6.7.0-5-Q16-windows-dll.exe

Install ImageMagick:
*Important: The installation path should NOT contain any spaces. Ideally select “C:\ImageMagick-6.7.0-Q16”

Please make sure to select the below options:

Step 2:
Installing rmagick:

Use the following command to install rmagick gem:

gem install rmagick --version=2.12.2 --platform=ruby -- --with-opt-lib=c:/ImageMagick-6.7.0-Q16/lib --with-opt-include=c:/ImageMagick-6.7.0-Q16/include

Most of the rmagick components have no documentation. So don’t worry about the “no rdoc”/”no ri” warnings.

Happy coding !!!

Class Instance Variables

Adhiraj — Sun, 16 May 2010 08:00:29 +0000

Ruby has a unique concept, namely Class Instance Variables that is not common in other programming languages. Ruby has instance variables, class variables and class instance variables. Lets take a quick look at what I am talking about.

Example 1
class Resource   @@developers = []
  def self.developers     return @@developers   end
  def add_to_pool     @@developers << self   end
  def initialize(resource_name)     @resource_name = resource_name   end end
Resource.new(‘Matz’).add_to_pool Resource.new(‘David’).add_to_pool Resource.new(‘James’).add_to_pool
puts Resource.developers.size    # 3

The output is pretty obvious here. Now lets consider a practical problem with this approach.

Example 2
class RubyDeveloper < Resource; end class JavaDeveloper < Resource; end
RubyDeveloper.new(‘Matz’).add_to_pool RubyDeveloper.new(‘David’).add_to_pool
JavaDeveloper.new(‘James’).add_to_pool
puts RubyDeveloper.developers.size # ? puts JavaDeveloper.developers.size # ?

The output here is:
>3
>3

Here’s the problem, how do we restrict the class variable to a given class and prevent any modification by its subclass?

Class Instance Variables to the rescue

Example 3
class Resource
  class << self     def developers       return @developers     end
    def developers=(developers)       @developers | |= [ ]     end   end
  def add_to_pool     self.class. developers | |= [ ]     self.class. developers << self   end
  def initialize(resource_name)     @resource_name = resource_name   end end
class RubyDeveloper < Resource; end class JavaDeveloper < Resource; end
RubyDeveloper.new(‘Matz’).add_to_pool RubyDeveloper.new(‘David’).add_to_pool
JavaDeveloper.new(‘James’).add_to_pool
puts RubyDeveloper.developers.size    # 2 puts JavaDeveloper.developers.size    # 1

Simplifying the code:
class << self def developers return @developers end
def developers=(developers) @developers | |= [ ] end end

can be achieved by:
class << self attr_accessor :developers end

Rewriting the Resource class
class Resource   class << self; attr_accessor :developers; end
  def add_to_pool     self.class. developers | |= [ ]     self.class. developers << self   end
  def initialize(resource_name)     @resource_name = resource_name   end end

Just to summarize:

Declaring the Class Instance Variable:
class << self; attr_accessor :developers; end

Accessing the Class Instance Variable:

Inside the class, where self is the class object:
self.developers

Inside an action in the class, where self is the instance:
self.class.developers

Hope that was interesting.
Happy coding!!!

Access Control in Ruby

Adhiraj — Sun, 02 May 2010 08:00:00 +0000

After stumbling upon the access level modifiers for a long time, one day I decided to understand the ins-and-outs about the concept of public, protected and private in Ruby.

Let’s understand the concept of Access Control in Ruby with the help of some simple examples:

Understanding Private methods in Ruby:

Example 1
def MyClass   def one     puts “From one”   end
  def two     one   end
  private :one end

mc = MyClass.new mc.two # From one

NOTE: In the method “two”, the implicit receiver is “self”, where “self” is the instance “mc”
Pretty obvious output, as expected.

Let’s take a deep dive:

Example 2
class MyClass   def one     puts “From one”   end
  def two     MyClass.new.one   end
  private :one end

mc = MyClass.new mc.two # ?

The output here is:
NoMethodError: private method ‘one’ called for

Before we get into the details, let’s consider a couple more examples:

Example 3
class MyClass   def one     puts “From one”   end
  def two     self.one   end
  private :one end

mc = MyClass.new mc.two # ?

The output here is:
NoMethodError: private method ‘one’ called for

One last example with private and we should be good to conclude.

Example 4
class MyClass   def one     puts “From one”   end
  private :one end
class MySubClass < MyClass   def two     one   end end

mc = MySubClass.new mc.two # ?

The output here is:
>From one

To conclude:

Private Visibility:

1. Private methods are private to the instance (and not to the class).
2. Private methods are accessible from sub-classes.
3. While accessing private methods, you cannot specify the receiver (even if its “self”), receiver is always implicit, never explicit.
4. “Private” in Ruby is what “Protected” is in many other languages.
5. In Ruby, no method is perfectly private or hidden.

Understanding Protected methods in Ruby:

Example 5
class MyClass   def one     puts “From one”   end
  def two     one     MyClass.new.one     self.one   end
  private :one end

mc = MyClass.new mc.two # ?

The output here is:
>From one
>From one
>From one

To conclude:

Protected Visibility:

1. Protected methods are visible to all the instances of the same class as well as sub-classes.
2. Protected methods are also accessible from sub-classes. In short, Access control in Ruby neither applies to nor impacts the object hierarchy.
3. While accessing protected methods, you can specify the receiver, receiver can by explicit or implicit.
4. “Protected” in Ruby is not quite common in other programming languages.
5. What’s the use if its accessible to all the instances as well as from sub-classes?
Private and Protected methods are not directly accessible outside the class.

Public Visibility:

1. The default access level is “Public”. Public methods are accessible from anywhere*.
(*anywhere – within the class, outside the class, same instance, other instances of same class and sub-classes)

Important: Also, in a subclass, one can override the access level modifier specified for any given action in the parent class.

Hope this helps understanding the basics of Access Control in Ruby. As always said, Ruby is truly object-oriented.
With this said, Access Level Modifiers should not be a hurdle hereon.

Food for Thought:
Private and Protected method declaration in Ruby is by-passed by the
message sending syntax.
class MyClass def one puts “From one” end
private :one end

mc = MyClass.new mc.one # NoMethodError: private method 'one' called for

mc.send(:one) # From one

I haven’t been able to figure out the reason for this ambiguity in Ruby, the research is still on. If anyone has any ideas, please keep me posted.

In Ruby 1.9, we have a new method defined in the “Object” class named “public_send”. This respects the access level modifiers specified for any given action.

Happy coding !!!

Riding Rails on Ruby Enterprise Edition

Adhiraj — Sun, 21 Mar 2010 08:00:33 +0000

Passenger allows Ruby on Rails applications to use about 33% less memory, when used in combination with Ruby Enterprise Edition

I am putting down steps to install Ruby Enterprise Edition and configure Passenger to use Ruby Enterprise Edition

Download Ruby Enterprise Edition

You can download Ruby Enterprise Edition here.

Or through terminal,

wget http://rubyforge.org/frs/download.php/68719/ruby-enterprise-X.X.X-YYYY.MM.tar.gz

Install Ruby Enterprise Edition

Extract the files:

tar -xvzf ruby-enterprise-X.X.X.tar.gz

Run the installer. As root,

./ruby-enterprise-X.X.X/installer

Set the path environment variable:

vim ~/.bash_profile

Add the following line:

export PATH=/opt/ruby-enterprise-X.X.X-YYYY.MM/bin:$PATH

Load the path environment variable in the current session:

As root,

source ~/.bash_profile

That’s it, we are done installing Ruby Enterprise Edition.

You can verify by:

ruby -v

ruby 1.8.7 (2009-12-24 patchlevel 248) [x86_64-linux], MBARI 0x6770, Ruby Enterprise Edition 2010.01

DO remember that this is a fresh installation of Ruby, that implies, you need to install all the necessary gems again. Ruby Enterprise Edition by default installs the latest stable version of Rails and the Passenger gem as well.

Now you can install and configure the Passenger module for Apache as described in article found at https://adhirajrankhambe.wordpress.com/2010/03/20/riding-rails-the-php-way/.

References:

http://www.rubyenterpriseedition.com/
http://www.rubyenterpriseedition.com/documentation.html

Riding Rails the PHP way

Adhiraj — Sat, 20 Mar 2010 08:00:52 +0000

I have been working with PHP for quite some time now, though my first love has always been Ruby on Rails :)

While working with PHP, I realized that deployment of a PHP application is far more easier as compared to deployment of a Ruby on Rails application. So I was wondering if there could be a way to deploy a Ruby on Rails application in a similar fashion, as easy as you check out the Rails project in a directory on the server, configure a VirtualHost in the webserver, restart the webserver and there you go, everything should work as expected.

Luckily I did find a saviour,

“Phusion Passenger” a.k.a “mod_rails” or “mod_rack”

Here I am putting down steps to ride Rails on Passenger.

Install Passenger

Passenger is available as a Rubygem. As root,

gem install passenger

Install Passenger module for Apache

passenger-install-apache2-module

During installation it will prompt:

The Apache2 module was successfully installed.

Please edit your Apache configuration file, and add these lines:

LoadModule passenger_module /usr/lib64/ruby/gems/1.8/gems/passenger-2.2.11/ext/apache2/mod_passenger.so PassengerRoot /usr/lib64/ruby/gems/1.8/gems/passenger-2.2.11 PassengerRuby /usr/bin/ruby

NOTE: Do NOT copy-paste from here. Make sure you add the lines that passenger prompts you with.
It is specific to the OS installation. Mine was a Fedora Core 10 64-bit installation.

Next, it will help you to configure a VirtualHost for Apache

ServerName www.yourhost.com DocumentRoot /somewhere/public
AllowOverride all Options -MultiViews


Restart Apache:
As root,
/sbin/service httpd restart
That's it, we are done.

Point your browser to your domain, and you should be able to see your Ruby on Rails Application.
Do keep in mind that the default Rails environment while using Passenger is “production”

To access your application in “development” or any other environment add the following line in your VirtualHost configuration:
RailsEnv development
Restarting your application deployed in production environment:
To restart your Rails application deployed in production environment you can restart Apache.

But that's not a good solution if you are hosting multiple applications on the same server, or even generally, it doesn't sound like a good idea to restart Apache every now and then.

To overcome that, you can restart your application in the following way:
From Rails Root Directory,
touch tmp/restart.txt
That's it, this will restart you Rails application.
The best part is, Passenger is compatible with all the Rubygems and Rails plugins.
So nothing should break. I personally tried running a complex Rails application that uses Solr as the search engine along with acts_as_solr plugin, backgroundRB server for background processes, attachment_fu for file uploads etc, etc.
Everything worked like a charm.
For further configuration, please refer to the Passenger documentation found here:
You can also use Passenger to serve Non-Rails Ruby web applications. That can be a good alternative to the already prevalent mod_ruby module for Apache.

If you are using Nginx as your webserver, you can use Passenger module for Nginx.
There's just one disadvantage to Passenger:
It doesn't work on Windows. In any case, I personally never prefer to develop Rails (or any other) applications on Windows :)
Good news for Mac users:
fingertips has come up with an OS X preference pane for Phusion Passenger (a.k.a. mod_rails) that makes it a cinch to deploy Rails applications using Passenger on the Mac. It can be as simple as dragging a Rails application folder onto the preference pane! This is absolutely ideal for quick and easy Rails development on OS X.
You can download the Passenger Preference Pane here
References:
http://www.modrails.com/documentation/Users%20guide%20Apache.html



Firefox Add-Ons I cannot live without
Adhiraj — Sun, 28 Feb 2010 08:00:51 +0000
Why Firefox?

Before listing the Firefox Add-Ons I cannot live without, let me praise Firefox, the browser I cannot live without.
Firefox is undoubtedly the world’s best browser independent of any operating system. Be it Windows, Linux or Macintosh, Firefox with its Open-Source community support, huge number of Add-Ons and other features stands out to be the best-in-class web browser.
Being a software developer, I use three operating systems in a day, namely Linux for Ruby on Rails, Mac for iPhone application development ( and Windows for entertainment :) ) making Firefox the obvious choice for web browser that I can stick to.
Thanks to Mozilla for giving us Firefox, so that we don’t need to change web browsers depending on the Operating System we are using.
If you haven’t used Firefox yet, I would strongly recommend you to try it out.

I can go on and on praising Firefox, but let’s get over it.

Below I list my favourite Firefox Add-Ons categorized under Developer (5), Social Networking (3), Media (3) and Utility (3) add-ons.
Developer Add-Ons

1.	Firebug
Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

https://addons.mozilla.org/en-US/firefox/addon/1843
2.	Web Developer
The Web Developer extension adds a menu and a toolbar with various web developer tools.

https://addons.mozilla.org/en-US/firefox/addon/60
3.	MeasureIt
Draw out a ruler to get the pixel width and height of any elements on a webpage.

https://addons.mozilla.org/en-US/firefox/addon/539
4.	FireFTP
FireFTP is a free, secure, cross-platform FTP client for Mozilla Firefox which provides easy and intuitive access to FTP servers.

Along with transferring your files quickly and efficiently, FireFTP also includes more advanced features such as: directory comparison, syncing directories while navigating, SFTP, SSL encryption, search/filtering, integrity checks, remote editing, drag & drop, file hashing, and much more!

https://addons.mozilla.org/en-US/firefox/addon/684
5.	Greasemonkey
Allows you to customize the way a webpage displays using small bits of JavaScript.

Hundreds of scripts, for a wide variety of popular sites, are already available at http://userscripts.org.

You can write your own scripts, too. Check out http://wiki.greasespot.net/ to get started.

https://addons.mozilla.org/en-US/firefox/addon/748
Social Networking Add-Ons

1.	Delicious Bookmarks
Delicious Bookmarks is the official Firefox add-on for Delicious, the world’s leading social bookmarking service (formerly del.icio.us). It integrates your bookmarks and tags with Firefox and keeps them in sync for easy, convenient access.

https://addons.mozilla.org/en-US/firefox/addon/3615
2.	AddThis
AddThis for Firefox is the best add-on to make sharing and bookmarking simple. Have all your favorite web 2.0 social networking, bookmarking, blogging, and e-mail services at your fingertips. Share any page, anytime, with anyone.

https://addons.mozilla.org/en-US/firefox/addon/4076
3.	Yoono
Yoono is a powerful but easy to use sidebar for Firefox that helps you simplify your online social life by connecting you to Facebook, MySpace, Twitter, LinkedIn, Flickr, Friendfeed, AIM, Yahoo IM and more…all in one place. Yoono is also the easiest way to share stuff with all your social networks – share links, images and video from the page you’re viewing across all your networks simultaneously.

https://addons.mozilla.org/en-US/firefox/addon/1833
Media Add-Ons

1.	Cooliris
The Cooliris 3D Wall — Simply the fastest and most stunning way to browse photos and videos from the Web or your desktop. Effortlessly scroll an infinite “3D Wall” of your content from Facebook, Google Images, YouTube, Flickr, and hundreds more.

https://addons.mozilla.org/en-US/firefox/addon/5579
2.	Easy YouTube Video Downloader
Easiest Youtube video downloader ever, single click non-intrusive direct download buttons for FLV, 3GP, MP3, MP4, 720p HD and 1080p Full-HD qualities.

https://addons.mozilla.org/en-US/firefox/addon/10137
3.	RealPlayer Browser Record Plugin
Detects all recordable content on browser.

https://addons.mozilla.org/en-US/firefox/browse/type:7
Utility Add-Ons

1.	Google Gears
Gears is an open source project that enables more powerful web applications, by adding new features to your web browser.

http://gears.google.com/

(Google Gears Portable – https://addons.mozilla.org/en-US/firefox/addon/13492)
2.	FireShot
FireShot is a Firefox extension that creates screenshots of web pages (entirely or just visible part).

Unlike other extensions, this plugin provides a set of editing and annotation tools, which let users quickly modify web captures and insert text annotations and graphical annotations. Such functionality will be especially useful for web designers, testers and content reviewers.

https://addons.mozilla.org/en-US/firefox/addon/5648
3.	ReminderFox
ReminderFox displays and manages lists of reminders and ToDo’s. ReminderFox makes sure you remember all of your important dates via easy-to-use lists, alerts, and alarms, right in your browser without the need for a separate calendar program.

https://addons.mozilla.org/en-US/firefox/addon/1191
View all Firefox Add-Ons at https://addons.mozilla.org/




Installing Chrome with Flash on Linux (Fedora)
Adhiraj — Sun, 07 Feb 2010 08:00:32 +0000
Get Chrome
Download rpm here
32 bit .rpm (For Fedora/openSUSE)
OR
64 bit .rpm (For Fedora/openSUSE)
Install Chrome
Go to the directory where the file was downloaded and install the rpm:
rpm -ivh google-chrome-beta_current_i386.rpm
OR
rpm -ivh google-chrome-beta_current_x86_64.rpm
Get Flash
Download rpm from here
Step 1 of 2
Select an operating system:

Linux
Step 2 of 2
Select version to download:

Flash Player 10 for Linux (.rpm)
Install Flash
Go to the directory where the file was downloaded and install the rpm:
rpm -ivh flash-plugin-10.0.45.2-release.i386.rpm
Get the Browser Flash Plugin:
For 32 bit OS, when you install Flash player it automatically installs the Flash plugin for Firefox, which can be reused for Chrome.
For 64 bit OS, you can get the Browser Flash plugin here
Install the Browser Flash plugin for Chrome:
For 32 bit OS, you can just copy libflashplayer.so from /usr/lib/mozilla-firefox/plugins/ to /opt/google/chrome/plugins directory (You might need to create a plugins directory if its not already present).



mkdir /opt/google/chrome/plugins

cp /usr/lib/mozilla-firefox/plugins/libflashplayer.so /opt/google/chrome/plugins
For 64 bit OS, extract the contents of libflashplayer-10.0.45.2.linux-x86_64.so.tar.gz:
tar -xvzf libflashplayer-10.0.45.2.linux-x86_64.so.tar.gz
Copy the file libflashplayer.so to /opt/google/chrome/plugins directory (You might need to create a plugins directory if its not already present).
mkdir /opt/google/chrome/plugins

cp libflashplayer.so /opt/google/chrome/plugins
Start Chrome from terminal:
Close all windows of your Chrome browser.

Go to the directory /opt/google/chrome and start chrome from terminal:
google-chrome –enable-plugins
That’s it… we are done… you can confirm the installation by typing about:plugins in the address bar.

It should list Shockwave Flash.






Install JDK on Linux in just 2 minutes
Adhiraj — Sun, 04 Oct 2009 08:00:25 +0000
NOTE: Instructions are specific to Fedora distributions
After stumbling over JDK installations on Fedora each and every time, I finally decided to put down the steps on paper so that I can refer back whenever required. Here’s a very easy step-by-step guide to install JDK on a Fedora Core installation.
1. Download JDK Installer here
Select the appropriate Platform: Linux x64 (I use a 64-bit Fedora Core installation)
Get the jdk-1_5_0_21-linux-amd64.bin package and not the jdk-1_5_0_21-linux-amd64-rpm.bin ( .bin and not rpm.bin )
2. Make the JDK Binary Installation file executable
As root,
chmod 755 jdk-1_5_0_21-linux-amd64.bin
3. Create a directory to install JDK /usr/share/sunjava (you can use a custom location)
mkdir /usr/share/sunjava
4. Execute the binary installation for JDK in the /usr/share/sunjava directory
cd /usr/share/sunjava
sh /path/to/jdk-1_5_0_21-linux-amd64.bin
After executing this command you will need to read through the License Agreement and type yes for the installer to actually start installing the software. Once installed it will create a folder “jdk1.5.0_21” in the /usr/share/sunjava directory.
5. Adding it to the path environment variable
As root,
vim ~/.bash_profile
Add the following lines:
JAVA_HOME=/usr/share/sunjava/jdk1.5.0_21

export JAVA_HOME
PATH=$JAVA_HOME/bin:$PATH:$HOME/bin

export PATH
6. Load the path environment variable in the current session
As root,
source ~/.bash_profile
We’re done, you can confirm by:
java –version
It should output something similar to:
java version “1.5.0_21”

Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_21)

Java HotSpot(TM) 64-Bit Server VM (build 1.5.0_21, mixed mode)
References:
http://fedorasolved.org/browser-solutions/sun-jdk




Global Settings File for Your Rails Application
Adhiraj — Sun, 06 Sep 2009 08:00:50 +0000
I was wondering if there could be a place in my Rails Application where I could define universal constants or configuration variables or “global switches” to switch a functionality on/off.

I don’t know if this is the best way to achieve this, but following is how I achieved it in my Rails application:
Create a settings.yml file and put it in /config/ directory
# This file can be used to store universal constants that can be changed from within the application
domain: http://www.yourdomain.com
key2: value2
Create a module ApplicationConfig
module ApplicationConfig

    $config = YAML::load_file "#{RAILS_ROOT}/config/settings.yml"
    def self.update_application_configuration

      File.open("#{RAILS_ROOT}/config/settings.yml", 'w') { |f| YAML.dump($config, f) }

    end

end
Save the file as application_config.rb and put it in /lib/ directory
In your Application Controller, include the ApplicationConfig module
# Filters added to this controller apply to all controllers in the application.

# Likewise, all the methods added will be available for all controllers.
class ApplicationController < ActionController::Base

      helper :all # include all helpers, all the time

      protect_from_forgery
      include ApplicationConfig
      # Scrub sensitive parameters from your log

      # filter_parameter_logging :password

end
Now you can access the global variables as follows:
$config["domain"]
$config["key2"]
And set the global variables as follows:
$config["domain"] = "www.yournewdomain.com"

ApplicationConfig.update_application_configuration
$config["key2"] = "newvalue2"

ApplicationConfig.update_application_configuration
Hope this helps.




Generating a Rails project preconfigured to use MySQL
Adhiraj — Sun, 02 Aug 2009 08:00:25 +0000
With the 2.0.2 release of Ruby on Rails, the default database has been switched from MySQL to SQLite3
So, now when you generate a Rails project using:
rails 
This is how the generated database.yml (Database configuration file) looks like:
# SQLite version 3.x

#   gem install sqlite3-ruby (not necessary on OS X Leopard)

development:

  adapter: sqlite3

  database: db/development.sqlite3

  pool: 5

  timeout: 5000
# Warning: The database defined as “test” will be erased and

# re-generated from your development database when you run “rake”.

# Do not set this db to the same as development or production.

test:

  adapter: sqlite3

  database: db/test.sqlite3

  pool: 5

  timeout: 5000
production:

  adapter: sqlite3

  database: db/production.sqlite3

  pool: 5

  timeout: 5000
But if you still want to use MySQL as the database for your Rails app you can generate your rails app by:
rails -d mysql  (options: mysql/oracle/postgresql/sqlite2/sqlite3/frontbase/ibm_db)
OR
rails --database=mysql  (options: mysql/oracle/postgresql/sqlite2/sqlite3/frontbase/ibm_db)
The database.yml file generated by this method looks like:
# MySQL.  Versions 4.1 and 5.0 are recommended.

#

# Install the MySQL driver:

#   gem install mysql

# On Mac OS X:

#   sudo gem install mysql — –with-mysql-dir=/usr/local/mysql

# On Mac OS X Leopard:

#   sudo env ARCHFLAGS=”-arch i386″ gem install mysql — –with-mysql-config=/usr/local/mysql/bin/mysql_config

#       This sets the ARCHFLAGS environment variable to your native architecture

# On Windows:

#   gem install mysql

#       Choose the win32 build.

#       Install MySQL and put its /bin directory on your path.

#

# And be sure to use new-style password hashing:

#   http://dev.mysql.com/doc/refman/5.0/en/old-client.html

development:

  adapter: mysql

  encoding: utf8

  reconnect: false

  database: _development

  pool: 5

  username: root

  password:

  # JRuby doesn’t support socket:

  host: 127.0.0.1

  #socket: /var/lib/mysql/mysql.sock
# Warning: The database defined as “test” will be erased and

# re-generated from your development database when you run “rake”.

# Do not set this db to the same as development or production.

test:

  adapter: mysql

  encoding: utf8

  reconnect: false

  database: _test

  pool: 5

  username: root

  password:

  # JRuby doesn’t support socket:

  host: 127.0.0.1

  #socket: /var/lib/mysql/mysql.sock
production:

  adapter: mysql

  encoding: utf8

  reconnect: false

  database: _production

  pool: 5

  username: root

  password:

  # JRuby doesn’t support socket:

  host: 127.0.0.1

  #socket: /var/lib/mysql/mysql.sock
If you always use MySQL as the default database for Rails applications you can change the shell variable (RAILS_DEFAULT_DATABASE) as follows:
(As root)
export RAILS_DEFAULT_DATABASE=mysql
References:
http://weblog.rubyonrails.org/2007/12/17/rails-2-0-2-some-new-defaults-and-a-few-fixes