Scale Ruby on rails Applicaiton + ROR Books To Study + Test cases in rails

An Awesome blog On digitalocean scaling ROR applicaiton

https://www.digitalocean.com/community/tutorials/scaling-ruby-on-rails-setting-up-a-dedicated-mysql-server-part-2


Best ROR books to study

http://www.devbattles.com/en/sand/post-1317-10+RoR+Books+You+Must+Have+on+Your+Bookshelf


How to write test cases in rails

http://everydayrails.com/2012/03/19/testing-series-rspec-models-factory-girl.html


Free Bootstrap Templates

http://www.bootstrapzero.com/bootstrap-templates


Learn Algorithms and Data Structure

https://discuss.codechef.com/questions/48877/data-structures-and-algorithms

http://jeffe.cs.illinois.edu/teaching/algorithms/

https://class.coursera.org/algo-004/lecture


Learn Angular Basics

https://leanpub.com/recipes-with-angular-js/read


Free Online Web Chat Room

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Ruby On Rails Questions

Question

Rails:

Basic:

1. What's new in rails 4?
2. Difference b/w rails 3 and rails 4?
3. Difference b/w rails 2 and rails 4?
4. Where will you write the reusable code for controller in rails 4 ? (concerns)
5. Where will you write the reusable code for model in rails 4 ? (concerns)
6. What are gems in rails?
7. What is difference b/w gems and plugins?
8. What is difference b/w symbol and string?
9. What is caching? What is russian doll caching?
10. Why don't we use page caching and action caching. Also drawbacks for the same?
11.  What is difference b/w string and symbol?
12. Multiple inheritance in rails? And how can we use multiple inheritance in rails?
13. Method Overloading in rails?
14. Difference b/w include, extend and require?
15. STI and Polymorphic associations?
16. Different Examples for polymorphic association?
17. About yield?
18. Difference b/w class variables and instance variables?
19. How will you get and set the values without using attr_accessible?
20. How will you store foreign key to another column name?
21. What is difference between include and join?
22. Difference b/w proc and lambda?
23. Practical use of proc and lambda?
24. What is DRY principal?
25. What are RESTful routes?
26.  How many actions generated by scaffold command in rails 4?
27. What in difference b/w put and patch?
28. What is difference b/w get, put and post?
29. How can you define constructor in rails?
30. What is use of map in rails?
31. Best tool for security measurement in rails?
32. How everything in object in rails?
33. What are dynamic finders?
34. What is difference between session and cookies?
35. Dynamic Methods in rails?
36. What is use of bang (!) operator in rails?
37. What is use of module?
38. Is rails interpreted or compiled language?
39. Which files load first environment.rb and application.rb ? Difference?
40. Access modifier  in rails?
41. Use of scope?
42. What are sweepers and observers? Difference?
43. Actions and method difference?
44. What are filters?
45. How render works? render is slow so how can we fast our rendering?
46. What does request.xhr do?
47. What is use js.erb file?
48. Difference b/w render and redirect?
49. How can we call third party service using ajax?
50. What is Eager loading and lazy loading?
51. What are validations? Give example?
52.  What is use of helper method?
53. Sql Injection and cross site forgery request?
54. What is difference b/w render and redirect?
55. What are different type of joins?
56. What are turbolinks?
57. String and symbol which is better to use? (string GC)
58. What is garbage collector?
59. What are callbacks? Types?
60. How around_filter works?
61. Create DB design for project timesheets?
62. Use and How index works?
63. Preference of columns for indexing?
64. How capistrano works?
65. if everything is an object in rails so how class keyword in an object?
66.  Steps to increase page load speed?
67. If we write redirect_to google.com in action ? will it come back to site? What will happen?
68. Which loads first: layout's html file application.html.erb or action's html file like index.html.erb?
69. If action is not available into the controller and html occurs for the action so will rails show error or not?
70. How file loads? or hierarchy for loading the controller files?(alphabetically loads file)
71. Use of config.ru?
72. How routes call to particular action? An idea about routing?
73. What are cron Jobs?
74.  How to connect multiple databases?
75. Can a model file connect to some other database in rails? How?
76. Middleware in rails?
77. What are alias in rails?
78. How to create runtime methods?
79. How to create singleton class? an example in rails? (logs)
80. What are mixins?
81. What are virtual attributes?
82. What are whitelist/strong parameters?
83. Why we use strong parameters in rails 4? Reason behind that?
84. What is use of super?
85. Why we use self? 
86. Why not we use multiple inheritance and method overloading in rails?
87. How many type of exceptions are in rails?
88. How to enable you logging on production mode?
89. Custom validations?
90. Open classes?
91. What are the use of initializers?
92. Is internationalization occurs in rails?
93. What is rake?
94. Best practice to define constants?
95. What are named scope in routing?
96. What is use of concern in routing?
97. What is use of transaction method in rails?
98. What type of threading used in rails 4?
99. Which javascript library use by default in rails 4?
100. What is use of assets in rails ? 

OOPS :

Ques1: What is a class and object?
Ques2: How will you define a class (Real Time example) ?
Ques3: Why we need to create a class and why objects are created for a class ?
Ques4: What is use of class ?
Ques5: What is polymorphism, inheritance etc. Some basic oops concepts ?

Difference b/w slim, haml and erb

As per the performance

Nice blog

https://sephinrothcn.wordpress.com/2014/04/14/slim-vs-haml-performance-perspective/

Puma configuration with capistrano

config/deploy.rb

# config valid only for Capistrano 3.1
lock '3.3.5'

set :application, 'application'
set :repo_url, 'ssh url for gtihub-repo'

# Default branch is :master
# ask :branch, proc { `git rev-parse --abbrev-ref HEAD`.chomp }

set :rvm_type, :system
set :rvm_ruby_version, 'ruby-2.2.2'
# set :rbenv_type, :user # or :system, depends on your rbenv setup
# set :rbenv_ruby, '2.2.0'
# set :rbenv_prefix, "RBENV_ROOT=#{fetch(:rbenv_path)} RBENV_VERSION=#{fetch(:rbenv_ruby)} #{fetch(:rbenv_path)}/bin/rbenv exec"
# set :rbenv_map_bins, %w{rake gem bundle ruby rails}
# set :rbenv_roles, :all # default value

# Default deploy_to directory is /var/www/my_app
set :deploy_to, "/var/www/rails_apps/#{fetch(:application)}"
set :deploy_user, 'username'
set :use_sudo, false
set :password, ask('Server password:', nil, echo: false)
set :branch, ENV['REVISION'] || ENV['BRANCH_NAME'] || 'release2'

set :ssh_options, {
  forward_agent: true,
  # verbose: :debug,
  # user: fetch(:deploy_user),
  # password: fetch(:password)
}

# Default value for :scm is :git
set :scm, :git

set :bundle_binstubs, nil

# Default value for :format is :pretty
# set :format, :pretty

# Default value for :log_level is :debug
# set :log_level, :debug

# Default value for :pty is false
# set :pty, true

# Default value for :linked_files is []
set :linked_files, %w{config/database.yml}

# Default value for linked_dirs is []
set :linked_dirs, %w{log tmp/pids tmp/cache tmp/sockets vendor/bundle public/system public/application}

# Default value for default_env is {}
# set :default_env, { path: "/opt/ruby/bin:$PATH" }

# Default value for keep_releases is 5
# set :keep_releases, 5
set :tmp_dir, "/home/username/tmp"

set :puma_rackup, -> { File.join(current_path, 'config.ru') }
set :puma_state, "#{shared_path}/tmp/pids/puma.state"
set :puma_pid, "#{shared_path}/tmp/pids/puma.pid"
set :puma_bind, "unix://#{shared_path}/tmp/sockets/puma.sock"    #accept array for multi-bind
set :puma_conf, "#{shared_path}/puma.rb"
set :puma_access_log, "#{shared_path}/log/puma_access.log"
set :puma_error_log, "#{shared_path}/log/puma_error.log"
set :puma_role, :app
set :puma_env, fetch(:rack_env, fetch(:rails_env, 'production'))
set :puma_threads, [0, 8]
set :puma_workers, 1
set :puma_worker_timeout, nil
set :puma_init_active_record, false
set :puma_preload_app, false
set :puma_prune_bundler, true
set :nginx_config_name, 'application'

# set :nginx_sites_available_path, "/usr/local/nginx/sites-available"
# set :nginx_sites_enabled_path, "/usr/local/nginx/sites-enabled"

namespace :deploy do

  after :restart, :clear_cache do
    on roles(:web), in: :groups, limit: 3, wait: 10 do
      # Here we can do anything such as:
      # within release_path do
      #   execute :rake, 'cache:clear'
      # end
    end
  end

end

config/deploy/production.rb

server 'server-address', user: 'username', roles: %w{web app db}
set :nginx_server_name, 'server-address'
set :rails_env, :production

Build gem from Scratch

$ bundle gem lorem
      create  lorem/Gemfile
      create  lorem/Rakefile
      create  lorem/.gitignore
      create  lorem/lorem.gemspec
      create  lorem/lib/lorem.rb
      create  lorem/lib/lorem/version.rb

Initializating git repo in /Users/eifion/code/ep245/lorem

The bundle gem command creates a new directory and generates several files in it. It also initializes a git repository there. This assumes that you’re using git and we’ll explain why it does this shortly. Before we do that we’ll walk you through some of the generated files, starting with the lorem.gemspec file.

/lorem/lorem.gemspec

# -*- encoding: utf-8 -*-
$:.push File.expand_path("../lib", __FILE__)
require "lorem/version"
 
Gem::Specification.new do |s|
  s.name        = "lorem"
  s.version     = Lorem::VERSION
  s.platform    = Gem::Platform::RUBY
  s.authors     = ["TODO: Write your name"]
  s.email       = ["TODO: Write your email address"]
  s.homepage    = ""
  s.summary     = %q{TODO: Write a gem summary}
  s.description = %q{TODO: Write a gem description}
 
  s.rubyforge_project = "lorem"
 
  s.files         = `git ls-files`.split("\n")
  s.test_files    = `git ls-files -- ↵
    {test,spec,features}/*`.split("\n")
  s.executables   = `git ls-files -- bin/*`.split("\n").map{ ↵
    |f| File.basename(f) }
  s.require_paths = ["lib"]
end

We can see straight away by looking at the TODO items that this file is designed to be edited directly. Once we complete these items we’ll have a working Gemspec file. One interesting part of this file are the file attributes towards the end of the file. Each of these is determined at runtime by using the git ls-files command by using git to determine the files that will be included in the gem and this is why bundle gem creates a git repository. The good thing about this is that it will automatically inherit the behaviour of the .gitignore file so that temporary files and the files we don’t want in our git repository (and therefore don’t want in our gem) are excluded. The defaults above will work for most gems but they can always be edited if we need different behaviour.

Another thing to note is how the version number is determined. This is defined as a constant called Lorem::VERSION and this value is defined in another file called version.rb in the lib/lorem directory. All this file does is define the version number.

/lib/lorem/version.rb
module Lorem
  VERSION = "0.0.1"
end
When it’s time to update our gem to a new version we can change the version number here and republish the gem.

The other file generated in the lib directory is called lorem.rb and it’s this file that’s loaded when someone requires our gem. We can put any code we like in this file or create other files in the lib directory and require them here. For our simple Lorem gem we’ll just create a class method called ipsum that returns some Lorem Ipsum text.

/lib/lorem.rb
module Lorem
  def self.ipsum
    "Lorem ipsum dolor sit amet, consectetur adipisicing ...."
  end
end
Publishing

So, we’ve finished our gem now and we’re ready to publish the first version. Before we do we’ll update the Gemspec file and replace the TODO text.

/lorem.gemspec
# -*- encoding: utf-8 -*-
$:.push File.expand_path("../lib", __FILE__)
require "lorem/version"
 
Gem::Specification.new do |s|
  s.name        = "lorem"
  s.version     = Lorem::VERSION
  s.platform    = Gem::Platform::RUBY
  s.authors     = ["Eifion Bedford"]
  s.email       = ["eifion@asciicasts.com"]
  s.homepage    = ""
  s.summary     = %q{Lorem ipsum generator}
  s.description = %q{Simply generates lorem ipsum text.}
 
  s.rubyforge_project = "lorem"
 
  s.files         = `git ls-files`.split("\n")
  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
  s.require_paths = ["lib"]
end
Then we can run the gem build command and point it to our Gemspec file.

$ gem build lorem.gemspec
WARNING:  no homepage specified
  Successfully built RubyGem
  Name: lorem
  Version: 0.0.1
  File: lorem-0.0.1.gem
This command generates a .gem file. If we were to run the gem push command now that would push the gem up to RubyGems.org and publish it so that others could install it.

Rails Deployment on Centos/Redhat

Centos
-------

$ yum -y update

Install the bundle containing development tools by executing the following command:

$ yum groupinstall -y 'development tools'

Some of the packages we need for this tutorial (e.g. libyaml-devel, nginx etc.) are not found within the official CentOS repository.

Run the following to add the EPEL repository:

$ sudo su -c 'rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm'

$ yum -y update

Finally, in order to install some additional libraries and tools, run the following command:

$ yum install -y curl-devel nano sqlite-devel libyaml-devel

$ curl -L get.rvm.io | bash -s stable

$ source ~/.profile
$ rvm reload

$ rvm requirements
(if got error "Requirements installation failed with status: 1")

$ rvm install 1.8.7

Close the connection and relogin to remove the error: RVM is not a funciton

$ rvm use 1.8.7-p374 --default

$ yum install git

---------------------------------------------------------------------------------------------

MySQL Install

To begin with, a simple MySQL install:


$ sudo yum install mysql-server mysql mysql-devel


Note that we have installed the development libs and headers with the 'mysql-devel' package. This package is required by the mysql Rubygems package which we install later in this article.
Start

We need to start the MySQL server to intiliaze the installation of the base MySQL databases.

$ sudo /etc/init.d/mysqld start

--------------------------------------------------------------------------------------------------------------


$ gem install passenger --no-ri --no-rdoc

$ yum install curl-devel httpd-devel 

The environment is now ready for the compilation. The process takes a few minutes and it’s started by the following command:

Unbale to restart the server

$ sudo chmod o+x "/home/user"

$ passenger-install-apache2-module  

$ ssh-keygen

$ cat id_rsa.pub >> ~/.ssh/authorized_keys

Note: once you've imported the public key, you can delete it from the server.

and finally set file permissions on the server:

$ chmod 700 ~/.ssh
$ chmod 600 ~/.ssh/authorized_keys 

The above permissions are required if StrictModes is set to yes in /etc/ssh/sshd_config (the default).

Ensure the correct SELinux contexts are set:

$ restorecon -Rv ~/.ssh 

Now when you login to the server you won't be prompted for a password (unless you entered a passphrase when you created your key pair). By default, ssh will first try to authenticate using keys. If no keys are found or authentication fails, then ssh will fall back to conventional password authentication.

Once you've checked you can successfully login to the server using your public/private key pair, you can disable password authentication completely by adding the following setting to your /etc/ssh/sshd_config file:

# Disable password authentication forcing use of keys

PasswordAuthentication no

# Enter home directory
cd

#Give permissions

sudo chown -R user:user /path/to/direcrtory        #directory should be application deployment folder
sudo chmod -R g+w /path/to/directory


Create a new virtual host for your application.

Open the /etc/httpd/conf/httpd.conf file and uncomment the following line

NameVirtualHost *:80
At the end of the file, add

<VirtualHost *:80>
   ServerName yourdomain.com
   ServerAlias www.yourdomain.com
   DocumentRoot /home/newUser/my_rails_app/public
   <Directory /home/newUser/my_rails_app/public>
      AllowOverride all
      Options -MultiViews
   </Directory>
  ErrorLog /var/log/httpd/my_rails_app_error.log
  CustomLog /var/log/httpd/my_rails_app_access.log common
</VirtualHost>
Restart apache for the changes to take effect

sudo /etc/init.d/httpd restart

-----------------------------------------------------------------------------------------------------------------------------

Add Gem to your Gemfile
gem 'capistrano'

$ capify .

 Unable to start the Phusion Passenger watchdog because


Permission denied on rvm folder
chcon -R -h -t httpd_sys_script_exec_t /home/user/.rvm/

Getting error:
Starting httpd: Warning: DocumentRoot [/home/user/apps/alc/current/public] does not exist
Solution
 sudo setsebool -P httpd_enable_homedirs 1

 sudo visudo

nano /etc/httpd/conf/httpd.conf
add this conf on httpd.conf
ServerName 127.0.0.1


--------------------------------------------------------------------------------------------------------------------------


Set Up on REDHAT
----------------

yum -y update

Install the bundle containing development tools by executing the following command:

yum groupinstall -y 'development tools'

yum install gcc-c++ patch readline readline-devel zlib zlib-devel
yum install libyaml-devel libffi-devel openssl-devel make
yum install bzip2 autoconf automake libtool bison iconv-devel

gpg --keyserver hkp://keys.gnupg.net --recv-keys D39DC0E3  #if got error: GPG signature verification failed for

curl -L get.rvm.io | bash -s stable

source /etc/profile.d/rvm.sh


---------------------------------------------------------------------------------------------

MySQL Install

To begin with, a simple MySQL install:


sudo yum install mysql-server mysql mysql-devel


Note that we have installed the development libs and headers with the 'mysql-devel' package. This package is required by the mysql Rubygems package which we install later in this article.
Start

We need to start the MySQL server to intiliaze the installation of the base MySQL databases.

sudo /etc/init.d/mysqld start

yum install curl-devel httpd-devel

Understanding on Singleton

Code for singleton pattern

require "singleton"

class SimpleLogger
  include Singleton

  def initialize
    @output = []
  end

  attr_reader :output

  def error(message)
    output << formatted_message(message, "ERROR")
  end

  def info(message)
    output << formatted_message(message, "INFO")
  end

  def write(filename)
    File.open(filename, "a") { |f| f << output.join }
  end

  private

  def formatted_message(message, message_type)
    "#{Time.now} | #{message_type}: #{message}\n"
  end
end

Upgradation rails 2 to rails 4 (Errors)

Some Errors are given below while migration of rails 2 to rails 4

• 'rake/rdoctask' is obsolete and no longer supported. Use 'rdoc/task' (available in RDoc 2.4.2+) instead.

require 'rake/rdoctask'

to

require 'rdoc/task'

• undefined method `attr_accessible' for

Add ‘gem 'protected_attributes' to Gemfile

• undefined method `link_to_function' for

Add patch in app/helpers/link_to_helper_function.rb

module LinkToFunctionHelper def link_to_function(name, *args, &block) html_options = args.extract_options!.symbolize_keys function = block_given? ? update_page(&block) : args[0] || '' onclick = "#{"#{html_options[:onclick]}; " if html_options[:onclick]}#{function}; return false;" href = html_options[:href] || '#' content_tag(:a, name, html_options.merge(:href => href, :onclick => onclick)) end end

• ActiveRecord::AssociationNotFoundError (Association named 'authorizations' was not found on User

Change in lib/authenticated_system.rb:108 to (if using restful-authentication)

User.includes(:roles => :authorizations).find_by_id(session[:user_id])

• undefined method `has_strings' for

Comment has_string wherever you find it.

• Unknown key: :order. Valid keys are: :class_name, :class, :foreign_key…

Change format something like that

has_many :commission_reports, :order => "volume_year DESC, volume_month DESC", :dependent => :destroytohas_many :commission_reports, -> { order "volume_year DESC, volume_month DESC" }, dependent: :destroy

• undefined method `on' for #<ActiveModel::Errors

Rails 4, the problem is that there's no "on" method for the Errors class anymore. We use "get". From

Change format something like that

@user.contact.errors.on(:attended_before)

 to

@user.contact.errors.get(:attended_before)

• undefined method `call' when doing a simple query

Change scope from all models from

scope :enquiry, where({:involvement => INVOLVEMENT_ENQUIRY, :archived => false})

to

scope :enquiry, -> { where({:involvement => INVOLVEMENT_ENQUIRY, :archived => false}) }

• Fix Typical Syntax on has_many like associations 

has_many :prices, -> { includes(:country).order("created_at desc") }, as: :priceable, dependent: :destroy, class_name: "Price"

• Undefined method confirmed_me?

remove :confirmable from model where we have defined the devise parameters eg User model if not using

• Unknown key: :include

Change has_many statement

• NoMethodError (undefined method `authenticated?' )

FInd authenticated?  and replace with devise method valid_password?

• NoMethodError (undefined method `forget_me' for

Copy forget_me method from restful-authentication to User model

• link_to_function and the view helper with postfix _tag doesn’t work in rails 4 so the solution is

Add  Gem  into the gem file

gem 'prototype-rails'

In rails 2 prototype was supported but in rails 3 the jquery supports so we get the errors like

• Keep in mind that the rails 2 already create a application.js and application.css in public folder so do not create same name files in assets folder. That can also give you conflicts.
• element.dispatchEvent is not a function

Go to layout and check application layout

Here you have include the app/assets and public/assets together

So keep in mind the hierarchy of inclusion of files, in short

first jquery

second prototype

referred link

http://learn.jquery.com/using-jquery-core/avoid-conflicts-other-libraries/

<script src="prototype.js"></script>

<script src="jquery.js"></script>

After that include below in head of the html file the below line

<script>jQuery.noConflict();</script>

• javascript_include_tag :default doesn’t work in rails 4
• calendar_date_select doesn’t work in rails 4
• LocalJump Error

This is due to the return keyword written in block. So remove return from the block.

• undefined method `scoped' for

scoped method has been deprecated from rails 4. use all on place of it.

• Search Or.. functionality was not working so change it that code

Replace div with some some id

• Move all the assets from public folder to app folder

restful_authentication to Devise Migration

• Add the following gem into your Gemfile
• gem 'devise'
• gem 'devise-encryptable'
• Run the following commands from console
• bundle intstall
• rails g devise:install
• In model file whatever you are using saving user information like user.rb
• devise :database_authenticatable, :registerable, :recoverable, :rememberable, :confirmable, :validatable, :encryptable, :encryptor => :restful_authentication_sha1

          Modules :encryptable and :encryptor => :restful_authentication_sha1 are important here.

• In config/initializers/devise.rb, configure as below

config.stretches = 1 config.pepper = ""

We are setting empty pepper and stretches to 1. This is how restful authentication works. It does not use stretches or pepper (by default).

( Note: You may find REST_AUTH_SITE_KEY in config/initializers/site_keys.rb )

In other case if You did set the REST_AUTH_SITE_KEY , then configure as below

config.stretches = 10
  config.pepper = "<YOUR_REST_AUTH_SITE_KEY>"

• If you're using :validatable you may have to adjust your minimum password length. Devise uses 8, restful_authentication uses 6.
• In config/initializers/devise.rb

                    config.password_length = 6..128

That is it for configuration. Now we have to change the table column names (without deleting them) to give devise what it wants. Here is the migration file I used. Change it according to your app's business logic.

• Add migration to change columns

class ConvertRaToDevise < ActiveRecord::Migration

def self.up

  rename_column :users, "crypted_password", "encrypted_password"

 change_column :users, "encrypted_password", :string, :limit => 128, :default => "", :null => false

  rename_column :users, "salt", "password_salt"

  change_column :users, "password_salt", :string, :default => "", :null => false

  add_column :users, "remember_created_at", :datetime

end

def self.down

  remove_column :users, "remember_created_at"

  rename_column :users, "encrypted_password", "crypted_password"

  change_column :users, "crypted_password", :string, :limit => 40

  rename_column :users, "password_salt", "salt"

  change_column :users, "salt", :string, :limit => 40

end

end

You will able to use devise as authentication for your project.

Rails 2 to 4 UpGradation (Initial Level Settings)

Steps to upgrade the rails from 2 to 4 (Initial Level Settings)

• Use latest ruby version first which is compatible with rails 4
• Upgrade your Gems
• Change versions for Gems into Gemfile .
• Find alternative for gems which have been deprecated.
• Comment some below gems if you have into you Gemfile
• gem "mongrel"
• gem "cgi_multipart_eof_fix" 
• gem "fastercsv", '1.5.0'
• gem “debugger"
• Remove versions for these two basic Gems
• gem 'mysql2'
• gem 'rake'
• Comment all the mime initializers in file config/initializers/mime_types.rb
• Add config.egger_load in all rails environments in files config/environments/*
• config.eager_load = true
• Change match keyword from file routes.rb to get

You will able to run rails server from console