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Basically Enumerable mixin gives collection classes a variety of traverse, search, sort methods.
understanding ruby blocks i.e. proc
blocks are statements of code written in ruby. one can take them as similar to c language macro's
Different ways to define blocks
a = proc do puts "hello" end a.call #=> hello b = lambda do |u| puts "hello #{u}" end b.call('sandip')#=> hello sandip c = proc {|user| puts user } c.call('sandip') #=> sandip Passing block to enumerator
Lets assume we have collection array of strings and we want to print it
a = ['hi', 'sandip', 'how', 'you', 'doing', '?'] => ["hi", "sandip", "how", "you", "doing", "?"] a.each {|w| puts w } q = proc {|w| puts w } => # a.each(&q) #=> hi sandip how you doing ? a.map{|r| q.call(r)} #=> hi sandip how you doing ? Understanding symbol#to_proc
Symbol has method to_proc which converts symbol to block where symbol is taken as method to be executed on first argument of proc
How to_proc got implemented inside Symbol class class Symbol def to_proc Proc.new { |*args| args.shift.__send__(self, *args) } end end Lets have some examples
v = :even?.to_proc # equivalent to proc {|a| a.even?} #=> # q = [1, 2, 3, 5, 67] q.map(&v) => [false, true, false, false, false] Is there any shortcut?
Yes, there is shortcut to have block passed to enumerators on the fly using ampersand followed by colon (i.e. symbol)
q = [1, 2, 3, 5, 67] q.map(&:even?) <=> q.map(&:even?.to_proc) q.map(&:even?.to_proc) #=> [false, true, false, false, false] q.map(&:even?) #=> [false, true, false, false, false] Some handy examples
[1, 2, 3, 5, 67].inject(&:+) #=> 78 [1, 2, 3, 5, 67].inject(:+) #=> 78 [1, 2, 3, 5, 67].any?(&:even?) #=> true [1, 2, 3, 5, 67].detect(&:even?) #=> 2 ['ruby', 'on', 'rails'].map(&:upcase) #=> ["RUBY", "ON", "RAILS"]

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`puts` converts ruby object into string by invoking to_s method on object. The default to_s prints the object's class and an encoding of the object id. In order to print human readable form of object use inspect
locs = Location.find_by_sql('select * from locations') Location Load (0.5ms) select * from locations Puts Object internally invokes to_s method on object to print locs.each do |l| # it calls to_s method on object puts l end #<Location:0x000000055bb328> #<Location:0x000000055bb058>
puts object followed by subsequent invoke of inspect method outputs readable object locs.each do |l| puts l.inspect # prints actual object end #<Location id: 15, name: "Annettaside3", street: "71838 Ritchie Cape", city: "East Destanystad", state: "Utah", zip: "58054", phone: 123456, other_phone: 987654, staff_strength: 40, is_active: true, created_at: "2012-01-25 11:17:26", updated_at: "2012-01-25 11:17:26", country_name: "Korea"> #<Location id: 16, name: "Sporerbury4", street: "73057 Jerad Shoal", city: "South Kyliefurt", state: "Delaware", zip: "46553-3376", phone: 123456, other_phone: 987654, staff_strength: 40, is_active: true, created_at: "2012-01-25 11:24:48", updated_at: "2012-01-25 11:24:48", country_name: "Australia">

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We all know Active Support library constantly keeps adding new extensions to ruby core library and hence rails framework.
Do you know now inside ruby class we can have class_attribute placeholder.
class A class_attribute :counter, :access_time end A.counter = 12 A.counter #=> 12 A.new.counter #=> 12
Inheritance class B < A end B.counter #=> 12 B.access_time #=> nil B.access_time = Time.now B.access_time #=> Wed Dec 28 18:55:06 +0530 2011 B.new.access_time #=> Wed Dec 28 18:55:06 +0530 2011 A.access_time = nil
Restricting instance from writing class_attributes
class V class_attribute :counter, :instance_writer => false end V.new.counter = 12 NoMethodError: undefined method `counter=' for #
Other ways
a_class = Class.new{class_atrribute :counter} a_class.counter = 13 a_class.counter #=> 13 a_class.new.counter #=> 13 p = Class.new { class_attribute :help, :instance_writer => false } p.new.help = 'Got a second!' NoMethodError: undefined method `help=' for #<#:0x7f8f9d5b1038> p.help = 'Got a second!' p.help #=> "Got a second!"

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Ruby language is dynamic and robust. We can define methods inside ruby classes at runtime.
# bash class A define_method :a do puts "hello" end define_method :greeting do |message| puts message end end A.new.a #=> hello A.new.greeting 'Ram ram' #=> Ram ram
Can you imagine using dynamic methods below 24 lines of code is optimized to just 8 lines
To know more on below code read # Earlier code class ApplicationController < ActionController::Base protect_from_forgery helper_method :current_staff, :current_employee, current_admin def authenticate_staff!(opts={}) current_staff || not_authorized end def current_staff current_user if current_user.is_a? Staff end def authenticate_employee!(opts={}) current_employee || not_authorized end def current_employee current_user if current_user.is_a? Employee end def authenticate_admin!(opts={}) current_admin || not_authorized end def current_admin current_user if current_user.is_a? Admin end end
# New Version using dynamic methods %w(Staff Employee Admin).each do |k| define_method "current_#{k.underscore}" do current_user if current_user.is_a?(k.constantize) end define_method "authenticate_#{k.underscore}!" do |opts={}| send("current_#{k.underscore}") || not_authorized end end

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Active Record Inheritance (ARI)

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requirement was to display decimal numbers which are having scale values present to be displayed in decimal format otherwise display them as integer.

Output expected
12.23 => 12.23
12.00 => 12


While rendering any object on html page by default "to_s" method gets executed. So, i overwrote "to_s" method of BigDecimal class as below.

Anyone having better solution. Please reply with your solutions. Many thanks!
Put below code in file "config/intializers/core_extensions.rb"

class BigDecimal alias :old_s :to_s def to_s return to_i.to_s if eql? to_i self.old_s end end

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Array of years using range
((yr=Date.current.year)-9..yr).to_a #=> [2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010]
Array of years using lambda
Array.new(10){|i| Date.current.year-i} #=> [2010, 2009, 2008, 2007, 2006, 2005, 2004, 2003, 2002, 2001]
Array of months
Date::MONTHNAMES.compact #=> ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]
Array of abbreviated months
Date::ABBR_MONTHNAMES.compact #=> ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
Array of abbreviated months with index (ps. collect_with_index is core extension method added to array)
Date::ABBR_MONTHNAMES.compact.collect_with_index{|m, i| [m, i]} #=> [["Jan", 1], ["Feb", 2], ["Mar", 3], ["Apr", 4], ["May", 5], ["Jun", 6], ["Jul", 7], ["Aug", 8], ["Sep", 9], ["Oct", 10], ["Nov", 11], ["Dec", 12]] OR Date::ABBR_MONTHNAMES.compact.each_with_index.collect{|m, i| [m, i+1]} #=> [["Jan", 1], ["Feb", 2], ["Mar", 3], ["Apr", 4], ["May", 5], ["Jun", 6], ["Jul", 7], ["Aug", 8], ["Sep", 9], ["Oct", 10], ["Nov", 11], ["Dec", 12]]

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Wrong English is an often problem while developing any website product as it gives bad view to website user and thus does direct impact on product. BOSSMan is a ruby gem that interacts with yahoo web service and provides a simplest way to overcome such errors.
Installation:
gem sources -a http://gems.github.com gem install jpignata-bossman Apply and get Application ID from yahoo developer network URl https://developer.apps.yahoo.com/ Make sure to note it for reference
Usage in ruby app
require 'rubygems' require 'bossman' include BOSSMan BOSSMan.application_id = "Your Application ID here"
Spelling Suggestions
text = BOSSMan::Search.spelling("gooogle") => #{"resultset_spell"=>[{"suggestion"=>"google"}], "responsecode"=>"200", "deephits"=>"1", "start"=>"0", "count"=>"1", "totalhits"=>"1"}}> text.suggestion => "google"
More sophisticated way of use -
1. Create a YML file containing list of kewords
2. Load YML file
3. Iterate YML hash to find out spell suggestions
Example: spelling.yml
1 keywords: 2 gooogle: 3 Barack Oabama: 4 Indian: 5 Latuur:
keywords = YAML.load_file('spelling.yml')['keywords'].keys puts "Correction suggested" keywords.each do |keyword| text = BOSSMan::Search.spelling(keyword) if defined? text.suggestion puts "#{keyword} => #{text.suggestion}" end end
Output
Correction suggested gooogle => google Barack Oabama => Barack Obama Latuur => Latour
Analyze suggestions manually and make neccesary corrections..

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Building PDF Document in ruby & rails application using prawn Library
Brief
Before getting started with this tutorial, I would like to thanks Greg and
Prawn team for their awesome work towards ruby and rails community.
Installing prawn (core, layout, format, security)
gem install prawn or
Add following line in rails environment file inside initializer block. config.gem 'prawn' Optionally you can specify version to be used and then run task rake gems:install Generating pdf using rails console ./script/console pdf = Prawn::Document.new It creates new pdf document object. Here you can additionally pass options parameters such as - Prawn::Document.new(:page_size => [11.32, 8.49], :page_layout => :portrait) Prawn::Document.new(A0) Here A0 is page size. Prawn::Document.new(:page_layout => :portrait, :left_margin => 10.mm, # different :right_margin => 1.cm, # units :top_margin => 0.1.dm, # work :bottom_margin => 0.01.m, # well :page_size => 'A4') pdf.text("Prawn Rocks") => 12 pdf.render_file('prawn.pdf') => # Here is output file generated [click]
Now let's go through other goodness of prawn. pdf = Prawn::Document.new('A3') do

1. FONTS [click]
# Specify font to be used or specify path to font file. font "times.ttf" font("/times.ttf")
2. TEXT [click]
text 'Sandip Ransing', :size => 41, :position => :center, :style => :bold
3. STROKE LINE [click]
stroke do rectangle [300,300], 100, 200 end
4. IMAGE [click]
Display Local file system Image image 'sandip.png', :height => 50, :position => :center, :border => 2 Scale Image image 'sandip.png', :scale => 0.5, :position => :left Display Remote image from Internet inside pdf require "open-uri" image open('http://t2.gstatic.com/images?q=tbn:kTG6gAKrnou2gM:http://www.facebook.com/profile/pic.php?uid=AAAAAQAQrLXvTWfyY2ANjttV8D1c0QAAAAnDHPFJe0pPFR84iIzXPKro&t=1") end
5. LINE BREAKS
movedown(20)
6. TABLE/GRID [click]
data = [ ["Name", {:text => 'Sandip Ransing', :font_style => :bold, :colspan => 4 }], ["Address", {:text => 'SHIVAJINAGAR, PUNE 411005', :colspan => 4 }], ["Landmark",{:text => 'NEAR FC COLLEGE', :colspan => 4 }], ["Mobile","9860648108", {:text => "", :colspan => 3 }], ["Education", {:text => "Bachelor in Computer Engineering", :colspan => 4 }], ["Vehicle", 'Hero Honda',"Reg. No.", {:text => "MH 12 EN 921", :colspan => 3 }], ["Additional", "GDCA", "class", 'First', ""], [{:text => "Areas of Speciality", :font_style => :bold}, {:text => "Ruby, Rails, Radiant, Asterisk, Adhearsion, Geokit, Prawn, ....,...", :font_style => :bold, :colspan => 4}], [{:text => "Website", :colspan => 2},{:text => "www.funonrails.com", :colspan => 3}], [{:text => "Company", :colspan => 2},{:text => "Josh Software", :colspan => 3}] ] table data, :border_style => :grid, #:underline_header :font_size => 10, :horizontal_padding => 6, :vertical_padding => 3, :border_width => 0.7, :column_widths => { 0 => 130, 1 => 100, 2 => 100, 3 => 100, 4 => 80 }, :position => :left, :align => { 0 => :left, 1 => :right, 2 => :left, 3 => :right, 4 => :right }
7. LINKS [click]
link_annotation([200, 200, 500, 40],:Border => [0,0,1], :A => { :Type => :Action, :S => :URI, :URI => Prawn::LiteralString.new("http://twitter.com/sandipransing") } ) link_annotation(([0, 100, 100, 150]), :Border => [0,0,1], :Dest => s"http://funonrails.com")
8. PDF Security [click]
encrypt_document :user_password => 'hello', :owner_password => 'railer', :permissions => { :print_document => false }
9. Prawn Inline Formatting
Prawn-format supports inline text formatting that gives user enough flexibility to use html tags. require 'prawn/format' text 'This is Strong text', :inline_format => true text 'This is bold text \n It should be on newline.', :inline_format => true

SAVE PDF File end pdf.render_file 'my.pdf' !!! NOTE: As of time now 'prawn-format' is incompatible with latest prawn gem, It is compatible with prawn version <= 0.6 s

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Before getting started with modules and mixins, lets first find out the need of module & mixins in OOP.

In object oriented programming languages multiple inheritance is basic paradigm (child class extends behavior of base class).

C++ supports multiple inheritance. Java does support same using interfaces.
In ruby language, multiple inheritance is achieved very easily using mixin of modules & classes and that makes ruby as powerful language.

Ruby has classes, modules. Modules can be included inside other classes (mixins) to achieve multiple inheritance.

Modules module Greeting # here below is the instance method # and that can be accessed using object of class ONLY def hi puts 'Guest' end end Module methods can be called using scope resolution operator (::) or dot operator (.)
Greeting::hi # => undefined method `hi' for Greeting:Module (NoMethodError) It is obivous to have an error because we are calling class method and that is not present inside module.

Mixins Lets include greeting module inside person class
class Person include Greeting end person = Person.new person.hi #=> "Guest" Lets see how module methods can be defined. It can be done using either self or class_name.
module Greeting # here below is the instance method # and that can be accessed using object of class ONLY def hi puts 'Guest' end # Below are module methods # this methods can be invoked # using Greeting::hi # OR Greeting.hi def self.hi puts 'hi Sandip' end # here is one more way to declare # module methods def Greeting.bye puts 'Bye Sandip!' end end Lets invoke methods
Greeting::hi #=> "hi Sandip" Greeting.bye #=> "Bye Sandip!" Extending class behavior using modules
class Person def self.included(base) base.extend Greeting end end Got easy ?? Cheers!

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Alias method in ruby
Ruby classes provides a alias_method that can be used to reuse the existing methods.
Consider a situation where you need different methods which has same code and ONLY they have different names.

In this case alias_method uses suits best choice instead duplicating same code or writing common method that will get used in all methods, as i did before. Example, I have methods search, home, index all are doing same functionality.
Old approach # URL / def index list end # URL /search def search list end #URL /home def home list end private def list # code here end Correct approach in ruby def index # code here end alias_method :home, :index alias_method :search, :index Attributes aliasing in ruby
Same way one can easily rename existing class attribute names using alias_attribute method.
alias_attribute(new_name, old_name) alias_attrinute :username, :login More practical use
while deprecating attributes, methods in gems, plugins, extensions, libraries always use aliases in order to maintain backward compatibility.
Got easy ??
that's where ruby rocks !

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Ruby On Rails Installation on fresh ubuntu machine

Installation steps are applicable to ubuntu versions interpid, karmic koala. Make necessary changes according to package manager provided by other linux operating systems in order install ruby and rails.

Before getting started to installations make sure to build essential packages on fresh ubutnu machine. Ubuntu machine has built in apt-get package manager and that i loves because it is very to use as compared to other OS.

sudo apt-get install build-essential

Now there are many versions of ruby available including latest 1.9.2
But would like to prefer ruby version 1.8.7 as it is the most stable version as of now. I would like to recommend installtion of Ruby Enterprise Edition (REE) version as it is uses minimal system resources and consumes less memory.

Instrunctions to setup normal ruby and rails environment

1. Install Ruby, Rails, MySQL, irb and neceesary packages using single command

sudo apt-get install ruby ri rdoc mysql-server libmysql-ruby ruby1.8-dev irb1.8 libdbd-mysql-perl libdbi-perl libmysql-ruby1.8 libmysqlclient15off libnet-daemon-perl libplrpc-perl libreadline-ruby1.8 libruby1.8 mysql-client-5.1 mysql-common mysql-server-5.1 rdoc1.8 ri1.8 ruby1.8 irb libopenssl-ruby libopenssl-ruby1.8 libhtml-template-perl mysql-server-core-5.1 libmysqlclient16 libreadline5 psmisc

2. Install ruby gems

wget http://rubyforge.org/frs/download.php/60718/rubygems-1.3.5.tgz
tar xvzf rubygems-1.3.5.tgz
cd rubygems-1.3.5
sudo ruby setup.rb

3. Create symbolic links to installation paths

sudo ln -s /usr/bin/gem1.8 /usr/local/bin/gem
sudo ln -s /usr/bin/ruby1.8 /usr/local/bin/ruby
sudo ln -s /usr/bin/rdoc1.8 /usr/local/bin/rdoc
sudo ln -s /usr/bin/ri1.8 /usr/local/bin/ri
sudo ln -s /usr/bin/irb1.8 /usr/local/bin/irb

4. Setup gemrc in order to avoid rdoc installation and to setup gem sources.
Add following lines to ~/.gemrc file

---
gem: --no-ri --no-rdoc
:benchmark: false
:verbose: true
:backtrace: false
:update_sources: true
:sources:
- http://gems.rubyforge.org
- http://gems.github.com
:bulk_threshold: 1000

5. Install rails

sudo gem install rails --no-rdoc --no-ri

Ruby Enterprise Edition i.e. REE (ruby 1.8.7) Installation

This will install ruby, rails, mysql, nginx and passenger

1. Download REE setup and install it

wget http://rubyforge.org/frs/download.php/68719/ruby-enterprise-1.8.7-2010.01.tar.gz /opt/ruby

cd /opt
./ruby/installer

2. Add ruby inside path

vi ~/.bashrc
# Add following line at the end of file
export PATH=/opt/ruby/bin:$PATH

Thanks to @vwadhwani!

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Command to download/copy rails api to work locally(offline) mode.

wget -mk www.api.rubyonrails.org

For more information click

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1. Ruby http://tryruby.org
2. Hpricot http://hpricot.com
3. Regular expressions http://rubular.com
4. Exceptions http://hoptoadapp.com/
5. Application Performance http://newrelic.com
6. Ruby Doc http://www.ruby-doc.org/
7. Rails API http://api.rubyonrails.org/
8. Ruby gems sources http://rubyforge.org / http://gems.github.com / http://gemcutter.org
9. Listing remote gems from source gem list --remote --source http://gems.github.com
10. List of Rails Plugins http://wiki.rubyonrails.org/rails/pages/Plugins
http://www.agilewebdevelopment.com/plugins

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Eval method in ruby executes string/expression passed as parameter.
Example:
irb > eval("5+3") => 8 irb > eval("a=5") => 5 irb > eval("b||=a") => 5
Its part of ruby meta-programming and not recommended approach unless there is no any alternative to do.

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require 'hpricot'
require 'net/http'
require 'rio'

# Pass website url to be scraped
url = "www.funonrails.com"

# Define filename to store file locally
file = "temp.html"
# Save page locally
rio(url) < rio (file)

# Open page through hpricot
doc = Hpricot(open(file))

Apply hpricot library to get right contents

doc.at("div.pageTitle")
doc/"div.pageTitle"
doc.search("div.entry")
doc//"div.pageTitle"

Hpricot API Reference click here

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Passing parameters

ruby input.rb TOI DH TimesNew

Accessing parameters

 # input.rb
 p ARGV
 # => ["TOI", "DH", "TimesNew"]
 p ARGV[0]
 # => "TOI"
 p ARGV[1]
 # => "DH"

Optparser : parses commandline options in more effective way using OptParser class. and we can access options as hashed parameters.

Passing parameters

ruby input.rb -P"The Times of India" --category"article"

Accessing parameters

 
 # input.rb
 require 'optparser'
 
 options = ARGV.getopts("P:", 'category')

 p options
 # => { 'P' => 'The Times of India', :category => 'article' }

 p options['P']
 # => "The Times of India"

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"Write      your       string            here   ".squeeze.strip
"This     is my      input  string     ".gsub(/ +/, ' ')
"Write      your       string          here   ".split('  ').join(' ')

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Below is ruby code to establish manual database connection.
require 'active_record' ActiveRecord::Base.establish_connection( :adapter => "mysql", :host => "localhost", :username => "root", :password => "abcd", :database => "funonrails" )
Snippet of database.yml file
common: &common adapter: mysql database: students_dev username: root password: host: localhost students_development: <<: *common database: students_dev students_production: <<: *common database: students
Load database configurations from yml file
dbconfig = YAML::load(File.open('database.yml')) ActiveRecord::Base.establish_connection( dbconfig[:students_development] )
Active Record Model & DB connection
class Student < ActiveRecord::Base establish_connection "students_production" set_table_name "student" set_primary_key "stud_number" end