Tuesday, October 23, 2012

Difference between Application server and Web Server

What is Application Server and Web Server? Your search ends here .. 

apache, nginx, IIS are web servers
mongrel, webrick, phusion passenger are app servers

App server is something which works with particular programming language and parses and executes the code
since mongrel and webrick can only work with rails, so they are app servers

Web servers are servers which can take the request from the browser.
Web servers normally works on port 80 though we can change the port in configuration 
since mongrel and webrick can take that request directly, so they can be thought of as web servers but web servers do have a lot of other functionality like request pipeline, load balancing etc.
App servers lack these functionalities.

About Mongrel server:
mongrel work as web as well as app server if you are talking about dev environment
but in production, mongrel alone can not work it will be too slow
so we need a web server in front of mongrel

Ruby On Rails Interview Preparation


1. Why Ruby on Rails?
Ans: There are lot of advantages of using ruby on rails
1. DRY Principal
2. Convention over Configuration
3. Gems and Plugins
4. Scaffolding
5. Pure OOP Concept
6. Rest Support
7. Rack support
8. Action Mailer
9. Rpc support
10. Rexml Support
11. etc..

2. Explain about the programming language ruby?
Ruby is the brain child of a Japanese programmer Matz. He created Ruby. It is a cross platform object oriented language. It helps you in knowing what your code does in your application. With legacy code it gives you the power of administration and organization tasks. Being open source, it did go into great lengths of development.
3. Explain about ruby names?
Classes, variables, methods, constants and modules can be referred by ruby names. When you want to distinguish between various names you can specify that by the first character of the name. Some of the names are used as reserve words which should not be used for any other purpose. A name can be lowercase letter, upper case letter, number, or an underscore, make sure that you follow the name by name characters.

4. What is the Difference between Symbol and String?
Ans: Symbol are same like string but both behaviors is different based on object_id, memory and process time (cpu time) Strings are mutable , Symbols are immutable.
Mutable objects can be changed after assignment while immutable objects can only be overwritten. For example

p "string object jak".object_id #=> 22956070
p "string object jak".object_id #=> 22956030
p "string object jak".object_id #=> 22956090

p :symbol_object_jak.object_id #=> 247378
p :symbol_object_jak.object_id #=> 247378
p :symbol_object_jak.object_id #=> 247378

p " string object jak ".to_sym.object_id #=> 247518
p " string object jak ".to_sym.object_id #=> 247518
p " string object jak ".to_sym.object_id #=> 247518

p :symbol_object_jak.to_s.object_id #=> 22704460
p :symbol_object_jak.to_s.object_id #=> 22687010
p :symbol_object_jak.to_s.object_id #=> 21141310

And also it will differ by process time

For example:

Testing two symbol values for equality (or non-equality) is faster than testing two string values for equality,

Note : Each unique string value has an associated symbol


5. What is Session and Cookies?
Ans: Session: are used to store user information on the server side.
cookies: are used to store information on the browser side or we can say client side
Session : say session[:user] = “arunkumar” it remains when the browser is not closed
6. What is request.xhr?
Ans: A request.xhr tells the controller that the new Ajax request has come, It always return Boolean values (TRUE or FALSE)
7. What is MVC? and how it Works?
Ans: MVC tends for Model-View-Controller, used by many languages like PHP, Perl, Python etc. The flow goes like this: Request first comes to the controller, controller finds and appropriate view and interacts with model, model interacts with your database and send the response to controller then controller based on the response give the output parameter to view, for Example your url is something like this:
http://localhost:3000/users/new
here users is your controller and new is your method, there must be a file in your views/users folder named new.html.erb, so once the submit button is pressed, User model or whatever defined in the rhtml form_for syntax, will be called and values will be stored into the database.

8. What things we can define in the model?
Ans: There are lot of things you can define in models few are:
1. Validations (like validates_presence_of, numeracility_of, format_of etc.)
2. Relationships(like has_one, has_many, HABTM etc.)
3. Callbacks(like before_save, after_save, before_create etc.)
4. Suppose you installed a plugin say validation_group, So you can also define validation_group settings in your model
5. ROR Queries in Sql
6. Active record Associations Relationship
9. What is ORM in Rails?
Ans: ORM tends for Object-Relationship-Model, it means that your Classes are mapped to table in the database, and Objects are directly mapped to the rows in the table.

10. How many Types of Associations Relationships does a Model has?
Ans: When you have more than one model in your rails application, you would need to create connection between those models. You can do this via associations. Active Record supports three types of associations:
one-to-one : A one-to-one relationship exists when one item has exactly one of another item. For example, a person has exactly one birthday or a dog has exactly one owner.
one-to-many : A one-to-many relationship exists when a single object can be a member of many other objects. For instance, one subject can have many books.
many-to-many : A many-to-many relationship exists when the first object is related to one or more of a second object, and the second object is related to one or many of the first object.
You indicate these associations by adding declarations to your models: has_one, has_many, belongs_to, and has_and_belongs_to_many.

11. Difference between render and redirect?
Ans:

render example:
 render :partial
 render :new
  It will render the template new.rhtml without
  calling or redirecting to the new action.


redirect example:
 redirect_to :controller => ‘users’, :action => ‘new’
  It forces the clients browser to request the
  new action.

12. What is the Difference between Static and Dynamic Scaffolding?
Ans: The Syntax of Static Scaffold is like this:
ruby script/generate scaffold User Comment
Where Comment is the model and User is your controller, So all n all static scaffold takes 2 parameter i.e your controller name and model name, whereas in dynamic scaffolding you have to define controller and model one by one.

13. How you run your Rails Application without creating database ?
Ans: You can run application by uncomment the line in environment.rb

Path => rootpath conf/ environment.rb

# Skip frameworks you're not going to use (only works if using vendor/rails)
    config.frameworks -= [ :action_web_service, :action_mailer,:active_record ]
14. How to use sql db or mysql db. without defining it in the database.yml
Ans: You can use ActiveRecord anywhere!

require 'rubygems'

require 'active_record'

ActiveRecord::Base.establish_connection({

:adapter => 'postgresql',

:user => 'foo',

:password => 'bar',

:database => 'whatever'

})

class Task <>

set_table_tame "a_legacy_thingie"

def utility_methods

update_attribute(:title, "yep")

end

end

Task.find(:first)

Etcetera. It’s ActiveRecord, you know what to do. Going wild:

ActiveRecord::Base.establish_connection(:adapter => "sqlite3",

:dbfile => ":memory:")

ActiveRecord::Schema.define(:version => 1) do

create_table :posts do |t|

t.string :title

t.text :excerpt, :body

end

end

class Post <>

validates_presence_of :title

end

Post.create(:title => "A new post!")

Post.create(:title => "Another post",

:excerpt => "The excerpt is an excerpt.")

puts Post.count

15. What are helpers and how to use helpers in ROR?
Ans: Helpers (“view helpers”) are modules that provide methods which are automatically usable in your view. They provide shortcuts to commonly used display code and a way for you to keep the programming out of your views. The purpose of a helper is to simplify the view. It’s best if the view file (RHTML/RXML) is short and sweet, so you can see the structure of the output.

16. What is Active Record?
Ans: Active Record are like Object Relational Mapping(ORM), where classes are mapped to table , objects are mapped to columns and object attributes are mapped to data in the table

17. Ruby Support Single Inheritance/Multiple Inheritance or Both?
Ans: Ruby Supports only Single Inheritance.
You can achieve Multiple Inheritance through MIXIN concept means you achieve using module by including it with classes.
18. How many types of callbacks available in ROR?
Ans:

(-) save
(-) valid
(1) before_validation
(2) before_validation_on_create
(-) validate
(-) validate_on_create
(3) after_validation
(4) after_validation_on_create
(5) before_save
(6) before_create
(-) create
(7) after_create
(8) after_save

19. WHAT CAN RAILS MIGRATION DO?
ANS:
create_table(name, options)
drop_table(name)
rename_table(old_name, new_name)
add_column(table_name, column_name, type, options)
rename_column(table_name, column_name, new_column_name)
change_column(table_name, column_name, type, options)
remove_column(table_name, column_name)
add_index(table_name, column_name, index_type)
remove_index(table_name, column_name)
Migrations support all the basic data types: string, text, integer, float, datetime, timestamp, time, date, binary and boolean:

string - is for small data types such as a title.
text - is for longer pieces of textual data, such as the description.
integer - is for whole numbers.
float - is for decimals.
datetime and timestamp - store the date and time into a column.
date and time - store either the date only or time only.
binary - is for storing data such as images, audio, or movies.
boolean - is for storing true or false values.
Valid column options are:

limit ( :limit => “50” )
default (:default => “blah” )
null (:null => false implies NOT NULL)

20. What is the naming conventions for methods that return a boolean result?
Ans: Methods that return a boolean result are typically named with a ending question mark. For example: def active? return true #just always returning true end

21. How do the following methods differ: @my_string.strip and @my_string.strip! ?
Ans: The strip! method modifies the variable directly. Calling strip (without the !) returns a copy of the variable with the modifications, the original variable is not altered.
22. What's the difference in scope for these two variables: @name and @@name?

Ans: @name is an instance variable and @@name is a class variable

23. What is the log that has to seen to check for an error in ruby rails?
Ans: Rails will report errors from Apache in log/apache.log and errors from the Ruby code in log/development.log. If you're having a problem, do have a look at what these logs are saying. On Unix and Mac OS X you may run tail -f log/development.log in a separate terminal to monitor your application's execution.
24. What is the use of global variable $ in Ruby?
Ans: A class variable starts with an @@ sign which is immediately followed by upper or lower case letter. You can also put some name characters after the letters which stand to be a pure optional. A class variable can be shared among all the objects of a class. A single copy of a class variable exists for each and every given class.
To write a global variable you start the variable with a $ sign which should be followed by a name character. Ruby defines a number of global variables which also include other punctuation characters such as $_ and $-k.
For example: If you declare one variable as global we can access any where, where as class variable visibility only in the class Example
class Test
def h
 $a = 5
 @b = 4
Â
while $a > 0
puts $a
$a= $a - 1
end
end
end
test = Test.new
test.h
puts $a                    # 5
puts @b                   #nil

25. Where does the start_tabnav gets informations for tabs rendering in ruby rail?
Ans: The main Symbol let the start_tabnav method know to look for a special MainTabnav class where all the magic happens

26. What is the Install rail package?
Ans: There are several packages that you can download and install. The prebuilt Rails installer called Install rail which currently is only for Windows
27. What is the log that has to seen to check for an error in ruby rails?
Ans: Rails will report errors from Apache in log/apache.log and errors from the Ruby code in log/development.log. If you're having a problem, do have a look at what these logs are saying. On Unix and Mac OS X you may run tail -f log/development.log in a separate terminal to monitor your application's execution.

28. What is the use of super in ruby rails?
Ans: Ruby uses the super keyword to call the superclass (Parent class) implementation of the current method

29. What is the difference between nil and false in ruby?
Ans: False is a boolean datatype, Nil is not a data type it have object_id 4

30. How is class methods defined in Ruby?
Ans: A:def self.methodname
--------
--------
end
or
def classname.methodname
--------
--------
end

31. How is object methods defined in Ruby?
Ans:
class jak
def method1
--------
--------
end
end

obj=jak.new
It is single object
def obj.object_method_one
--------
--------
end
obj.Send(object_method_every)
It will be created every for every object creation

32. What are the priority of operators available in Ruby ?
Ans: Something that used in an expression to manipulate objects such as + (plus), - (minus), * (multiply), and / (divide). You can also use operators to do comparisons,such as with <, >, and &&. The priority is based on "BODMAS"

33. What are the looping structures available in Ruby?
Ans: for..in
untill..end
while..end
do..end
Note: You can also use each to iterate a array as loop not exactly like loop
34. What are the object-oriented programming features supported by Ruby and how multiple inheritance supported in ?
Ans: Classes,Objects,Inheritance,Singleton methods,polymorphism(accomplished by over riding and overloading) are some oo concepts supported by ruby. Multiple inheritance supported using Mixin concept.
35. What is the scope of a local variable in Ruby and define it scope ?
Ans: A new scope for a local variable is introduced in the toplevel, a class (module) definition, a method defintion. In a procedure block a new scope is introduced but you can access to a local variable outside the block.
The scope in a block is special because a local variable should be localized in Thread and Proc objects.
36. How is an enumerator iterator handled in Ruby?
Ans: Iterator is handled using keyword 'each' in ruby.
For example
number=[1,2,3]
then we can use iterator as
number.each do |i|
puts i
end
Above prints the values of an array $no which is accomplished using iterator.
37. How is visibility of methods changed in Ruby (Encapsulation)?
Ans: By applying the access modifier : Public , Private and Protected access Modifier

38. What is the use of load,require, auto_load,require_relative in Ruby?
Ans: A method that loads and processes the Ruby code from a separate file, including whatever classes, modules, methods, and constants are in that file into the current scope. load is similar, but rather than performing the inclusion operation once, it reprocesses the code every time load is called.
auto_load - Whenever the interpreter call the method that time only it will initiate the method in hat file.
require_relative - It it to load local folder files.

More Questions:
1. Explain choose_weighted method with example
2. What is GIL in ruby ?
3. Is variable is a object ?
Ans : Variable is not an object
4. List of protocols supported by ruby ?
5. Explain Virtual attribute ?
6. How to validate and modify attribute value ?
7. How to serialize data with YAML ?

Thursday, August 9, 2012

Test Driven Development (TDD) in Ruby on Rails

Introduction

The purpose of this document is to describe the working principle of Ruby on Rails test frameworks, its application, advantages and disadvantages. This document contains an introduction to Test driven development (TDD).

Test  Driven Development (TDD)

            Test Driven Development is a development practice which involves writing test cases before writing the code. Start by writing a very small test for code that does not yet exist. Run the test and, naturally, it fails. Now we have to write the code to pass the test.ie, writing code only for the requirement. Large numbers of tests help to limit the number of defects in the code. The early and frequent nature of the testing helps to catch defects early in the development cycle, preventing them from becoming endemic and expensive problems.

TDD in Ruby on Rails
                   Ruby on rails supports test frameworks for Test Driven Development; A Test Framework is a tool or library that provides a backdrop for writing tests. This is an excellent way to build up a test suite that exercises every part of the application.
There are several testing frameworks in use for Ruby today:
  • Test::Unit is included with Ruby 1.8, and follows the "xUnit" conventions
  • Minitest is included with Ruby 1.9, and allows both xUnit and RSpec style tests
  • RSpec, which  has more concise syntax and can be used in the same project, but creates a separate suite of tests, called "specs"
  • In Cucumber, tests are written not in Ruby but in a language designed for tests
  • Rspec-2, which is used with Rails -3. Since We are using Rails -3 Rspec -2 is the best option we can use for test driven development
For using this, we have to twist thinking a little bit. Our goal is not to write eventual production code right away , but our goal is to make our test cases pass.
Work Flow Structure
We can structure the test driven workflow as follows:
  • First write a test: This test describes the behavior of a small element of your system. Tests in TDD are called programmer tests. When writing the tests it should be kept in mind that the tests should concentrate on testing the true behaviors, i.e. if a system has to handle multiple inputs, the tests should reflect multiple inputs.
  • Run the test:  The test definitely fails because you have not yet built the code for that part of your system. This important step tests your test case, verifying that your test case fails. The automatic tests should be run after each change of the application code in order to assure that the changes have not introduced errors to the previous version of the code
  • Write Code: Then only real coding comes, write enough code to make the test pass. In TDD, the code writing is actually a process for making the test work, i.e. writing the code that passes the test.
  • Run the test: Again run the test and verify that they pass.
·         Refactor the code - Refactoring is a process of improving the internal structure by editing the existing working code, without changing its external behavior. The idea of refactoring is to carry out the modifications as a series of small steps without introducing new defects into to the system
  • Run all tests:  To verify that the refactoring did not change the external behavior.
 See the Structure below:
     The first step involves simply writing a piece of code that tests the desired functionality. The second one is required to validate that the test is correct, i.e. the test must not pass at this point, because the behavior under implementation must not exist as yet. Nonetheless, if the test passes, the test is either not testing the correct behavior or the TDD principles have not been followed. The third step is the writing of the code. However, it should be kept in mind to only write as little code as possible to pass the. Next, all tests must be run in order to see that the change has not introduced any problems somewhere else in the system. Once all tests pass, the internal structure of the code should be improved by refactoring.

Rspec2
RSpec is a great tool in the behavior driven design process of writing human readable specifications that direct and validate the development of your application. What follows are some guidelines taken from the literature, online resources, and from our experience. Rspec is not a tool for Integration Testing but for Unit Testing, if you want to set up integration tests, then you should use Cucumber. Cucumber is designed to easy Behavior Driven Development but even if you don't BDD it is perfect for integration testing.
Examples  For Rspec-2  Test case
We can integrate Rspec to Ruby On Rails  by installing the Rspec2 gem.
            gem install rspec-rails

For this example, we’ll describe and develop the beginnings of a User class, which can be assigned any number of roles. Start by creating a directory for the files for this tutorial.
                   
                    * mkdir rspec_example
                    * cd rspec_example

 The first methods we’ll encounter are ` describe` and  `it`.
Create a file in this directory named user_spec.rb  and type the following:

describe User do
end

The describe method creates an instance of Behavior. So “describe User” is really saying “describe the behaviour of the User class”.
Run the following command:
               *  rspec spec/ user_spec.rb

     The rspec command gets installed when you install the rspec-rails gem. It supports   a large number of command line options.
     Running user_spec.rb should have resulted in output that includes the following error:
    ./user_spec.rb:1: uninitialized constant User (NameError)

We haven’t even written a single line of production code and already Rspec2 is telling us what code we need to write. We need to create a User class to resolve this error,



so create user.rb with the following:

class User
end
 And require it in user_spec.rb:
require 'user'

describe User do
end

Now run the rspec command again, will get a result like this
              
Finished in 6.0e-06 seconds
0 examples, 0 failures
The output shows that we have no examples yet, so let’s add one. We’ll start by describing the intent of example without any code.
describe User do
  it "should be in any roles assigned to it" do
  end
end

Run the spec, but this time adds the --format option:

$ rspec spec/user_spec.rb --format doc

User - should be in any roles assigned to it
Finished in 0.022865 seconds
1 example, 0 failures

Now add a Ruby statement that begins to express the described intent.

describe User do
  it "should be in any roles assigned to it" do
    user.should be_in_role ("assigned role")
  end
end

… and run the spec command.

$ rspec spec/user_spec.rb --format specdoc

User - should be in any roles assigned to it (ERROR - 1)

1) NameError in 'User should be in any roles assigned to it' undefined local variable or method `user' for #<#<Class:0x14ed15c>:0x14ecdd8> ./user_spec.rb:6:

Finished in 0.017956 seconds

1 example, 1 failure

The output tells us that there is an error that no user has been defined, so the next step is to make one:

describe User do
  it "should be in any roles assigned to it" do
    user = User.new
    user.should be_in_role ("assigned role")
  end
end

Run the spec command,
$ rspec spec/user_spec.rb --format specdoc

User - should be in any roles assigned to it (ERROR - 1)
1) NoMethodError in 'User should be in any roles assigned to it' undefined method `in_role?' for #<User:0x14ec8ec> ./user_spec.rb:7:
Finished in 0.020779 seconds
1 example, 1 failure

Now we learn that User does not respond to in_role?, so we add that to User:

class User
  def in_role?(role)
  end

$ rspec spec/user_spec.rb --format specdoc

User - should be in any roles assigned to it (FAILED - 1)
1) 'User should be in any roles assigned to it' FAILED expected in_role?("assigned role") to return true, 
got nil ./user_spec.rb:7:
Finished in 0.0172110000000001 seconds
1 example, 1 failure

We now have a failing example, which is the first goal. We always want to see a meaningful failure before 
success because that’s the only way we can be sure the success is the result of writing code in the right place in the system.

To get this to pass, we do the simplest thing that could possibly work:
Edit user.rb

class User
  def in_role?(role)
    true
  end


$ rspec spec/user_spec.rb --format specdoc

User - should be in any roles assigned to it
Finished in 0.018173 seconds
1 example, 0 failures

That passes, but we’re not done yet. Take a look again at the example:

describe User do
  it "should be in any roles assigned to it" do
    user = User.new
    user.should be_in_role("assigned role")
  end
end

The description says that the User “should be in any roles assigned to it”, but we haven’t assigned any roles to
 it. Let’s add that assignment to the example:

describe User do
  it "should be in any roles assigned to it" do
    user = User.new
    user.assign_role("assigned role")
    user.should be_in_role("assigned role")
  end
end

$ rspec spec/user_spec.rb --format specdoc

User - should be in any roles assigned to it (ERROR - 1)
1) NoMethodError in 'User should be in any roles assigned to it' undefined method `assign_role' for
 #<User:0x14ec784> ./user_spec.rb:6:
Finished in 0.018564 seconds
1 example, 1 failure

Following the advice in the output, we now add the assign_role method to User.

class User
  def in_role?(role)
    true
  end

  def assign_role(role)
  end
end

$ rspec spec/user_spec.rb --format specdoc

User - should be in any roles assigned to it
Finished in 0.018998 seconds
1 example, 0 failures


Advantages :
  • Testing improves your designs: Each target object that you test must have at least two clients: your production code, and your test case. These clients force you to decouple your code
  • Testing reduces unnecessary code: When you write your test cases first, you get in the habit of writing only enough code to make the test case pass. You reduce the temptation to code features because you might need them later.

  • Simple Development Procedure:  Each test case that you write establishes a small problem. Solving that problem with code is rewarding.

  • Testing allows more freedom:  If you have test cases that will catch likely errors, you'll find that you're more willing to make improvements to your code.

  • Efficient Product: If we can generate test cases for all the possible scenarios, then the result will be highly efficient, well documented product. TDD can lead to more modularized, flexible, and extensible code.

  • Documentation: After using this technique it satisfies a bunch of requirements, also have documentation, describing the behavior of the system, and a good start at a test suite. Each test case backs up a fundamental requirement in the system

Disadvantages :
  • Big time investment. For the simple case we lose about 20+% of the actual implementation, but for complicated cases you lose much more. Also more code to write. We have to create test cases  for models,  controllers  and  views ,which consumes a lot of time
  • Additional Complexity. For complex cases test cases are harder to calculate.
  •  Design Impacts. Sometimes the design is not clear at the start and evolves as we go along - this will force us to redo the test which will generate a big time lose
  • Continuous Tweaking. For data structures and black box algorithms unit tests would be perfect, but for algorithms that tend to be changed, tweaked or fine tuned, this can cause a big time investment that one might claim is not justified.

Monday, April 23, 2012

Who is already on Rails

Tens of thousands of Rails applications are already live. People are using Rails in the tiniest part-time operations to the biggest companies.

You know your Favourite Social Networking Website, www.twitter.com , using ROR...


Basecamp
Basecamp: The original Rails app.
Twitter
Twitter: Stay connected.

Shopify: E-commerce made easy.

Yellow Pages: Find it locally.
Github
Github: Git repo hosting.
Lighthouse
Livingsocial: Online local commerce.

Sortfolio: Find a web designer.

Hulu: Stream TV & Movies.
Groupon
Groupon: Daily deals.

Geni: Find your ancestors.

Backpack: Personal organization.

Ravelry: Knitting community.

43things: Your goals in life.

Justin TV: Live video.

Scribd: Books, presentations, more.

iLike: Find more music.

Streeteasy: Find a place in NYC.

Chow: Food, drink, fun.

Harvest: Tracking time since '06.

Inkling Markets: Trade the future.

A List Apart: 'zine for web devs.

Revolution Health: Get healthy.

New York Jets: Play ball!

Mingle2: Get a date.

VitalSource: Shopping for books.

Blinksale: Easy online invoicing.

Cookpad: Japanese dishes.

Blurb: Print your own book.

Tobi: 1-1 shopping.

Spock: Search for people.

Lumosity: Train your brain.

Lacoctelera: Spanish blogs.

A Better Tomorrow: T to the shirt.

Urban Baby: Hey junior!

Metrotwin: London meets NY.

Oracle Mix: Shape the DB.

43places: Go somewhere.

Iconbuffet: Shop royalty-free icons.

Highrise: Prepare for business.

Get Satisfaction: Customer service.

Penny Arcade: Comics for gamers.

Tadalist: Share simple todo lists.

Blingee: Fun photos.

Bleacher Report: Keep score.

43people: Meet someone.


Campfire: Group chat.

Insider Pages: Find local businesses.

Zendesk: Customer support

Odeo: Find. Play. Enjoy.

Seeking Alpha: Stock market site.

Pragmatic Bookshelf: Learn more.

Soundcloud: Move music.

iseekgolf: AU's #1 golf site.

Xing Marketplace: Reach pros.


Freckle: Time tracking.

Qype: Guide to the UK.

Moviepilot: German movie DB.

SUSE Studio: Build your distro.


Lots of others ....Now You can think of switcing to ROR...rt?..