Ruby on Rails Interview Questions & Answers

Best Ruby on Rails Interview Questions and Answers

Dear Readers, Welcome to Ruby on Rails Interview Questions have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Ruby on Rails. These Ruby on Rails Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many Medical Industry.

1. Why Ruby on Rails? 

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?

 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? 

 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?

 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? 

 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? 

 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? 

 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?

 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 secondobject, 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? 

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? 

 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 ? 

 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 

 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? 

 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 theprogramming 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? 

 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? 

 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? 

• (-) 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?

• 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?

 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! ?

 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? 

 @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?

 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?

 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 

 

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?

 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?

 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?

 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? 

 Ruby uses the super keyword to call the superclass implementation of the current method

 

29. What is the difference between nil and false in ruby? 

 False is a boolean datatype, Nil is not a data type it have object_id 4 

 

30. How is class methods defined in Ruby? 

 A:def self.methodname 

-------- 

-------- 

end 

or 

def classname.methodname 

-------- 

-------- 

end 

 

31. How is object methods defined in Ruby? 

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 operators available in Ruby? 

 Something that’s 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 &&. 

 

33. What are the looping structures available in Ruby?

 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?

 Classes,Objects,Inheritance,Singleton methods,polymorphism(accomplished by over riding and overloading) are some oo concepts supported by ruby.

 

35. What is the scope of a local variable in Ruby?

 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 iterator handled in Ruby?

 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?

 By applying the access modifier : Public , Private and Protected acces Modifier

 

38. What is the use of load and require in Ruby?

 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. 

 

39. Explain about class libraries in ruby? 

Ruby has a strong set of class libraries and it covers from a variety of domains such as thread programming, domains and data types. Also ruby is a new language and it also has additional libraries coming every day. Many of the new languages which do exist have huge libraries because of their age.

 

40. Explain about portability? 

Ruby language can be ported to many platforms. Ruby programs can be ported to many platforms without any modification to the source code. This feature made the language very useful and highly used by many programmers worldwide. Some of the platforms used are DOS, UNIX, WINDOWS, etc.

 

41. Explain about garbage collection feature of ruby? 

Ruby is an object oriented language and every object oriented language tends to allocate many objects during execution of the program. Ruby deletes unallocated and unused objects automatically. This feature can be controlled by applying proper syntax and program through ruby.

 

42. Explain about the command line options? 

Ruby`s language is executed from the command line like most of the scripting languages. Programming and behavior language environment can be controlled from the interpreter itself. Some of the commands which are used are as follows –d, -h, -e prog, -v, -T, -r lib, etc.

 

43. Explain about environment variables present in ruby? 

Following are some of the environment variables used to control the behavior programming of ruby. While programming ENV object lists some of the current variables. 

RUBYLIB path searches for libraries. Make sure that you separate each path with colons. RUBYOPT passes command line options to Ruby interpreter. There are many more which can be obtained by searching the huge pool of library.

 

44. Explain about the defined operator? 

Define operator defines whether a passed expression is defined or not. If the expression is defined it returns the description string or null if the expression is not 

defined. If a variable is defined it gets initialized. If method call is defined as true then method also gets defined. This is also the same case with super and 

yield.

 

45. Explain about methods? 

Methods in ruby basically perform two functions, named operation and the code present in the class which does a specific function. In Ruby all your algorithms live in methods which in turn is present on objects. Ruby does not have any provision for functions. Code present in Ruby is always a method of some object. Behind the scenes ruby gives you the flexibility to work with methods as functions if you are considering working with other languages.

 

46. Explain about normal method class? 

This function calls a method and it can take any number of arguments and expr. Make sure that you put an asterisk or an ampersand before the expression. Last expr argument can be declared with a hash without any braces. If you want to increase the size of the array value then make sure that you put an asterisk before expression. 

“::” can be used to separate the class from methods. 

 

47) How does ruby deal with extremely large numbers? 

Unlike other programming languages ruby deals with extremely large numbers it doesn’t have any barriers. There is no limit on the extent of limit of number usage. Ruby performs this function with two different classes they are fixnum and bignum. Fixnum represents easily managed small numbers and bignum represents big numbers. Ruby entirely handles the functioning of these two classes which leaves a programmer to concentrate on his arithmetic operations.

 

48) Explain about Float, Dig and Max? 

Float class is used whenever the function changes constantly. It acts as a sub class of numeric. They represent real characters by making use of the native 

architecture of the double precision floating point. 

Max is used whenever there is a huge need of Float. 

Dig is used whenever you want to represent a float in decimal digits.

 

49) Explain about interpolation? 

Interpolation is a very important process in Ruby. Interpolation is the process of inserting a string into a literal. There is only one way in which you can 

interpolate a string into a literal by placing a Hash (#) within {} open and close brackets. This refers to a new name to by referring to the copy of the original 

method.

 

50) Explain about ruby code blocks? 

Ruby code blocks form an important part of ruby and are very fun to use. With the help of this feature you can place your code between do-end and you can associate them with method invocations and you can get an impression that they are like parameters. They may appear near to a source of the code and adjacent to a method call. 

The code is not executed during the program execution but it is executed when the context of its appearance is met or when it enters a method.