Ruby On Rails Job Interview Questions

Q
What are some advantages of using Ruby on Rails?
A
Famed coder Yukihiro “Matz” Matsumoto designed Ruby to make programmers “happy”—Rails affords you all the advantages of Ruby, including simple syntax, an extensive library, and a quickly growing community. Here are some advantages to look for in the developer’s answer.
Programmer Productivity: The Ruby framework isn’t called “Rails” for no reason—testimonies abound around the web on how Rails can quickly carry an app from conception, through development, and into production in record speed.
Built-In Testing: Rails enables developers to use supporting code called harnesses and fixtures to quickly draft simple extendable automated tests.
Open-Source: Rails is open-source and 100% free, and its compatibility with Linux means there are many open-source options available when constructing your solution stack.
Metaprogramming: The ability to write code that acts on code rather than data can be a huge advantage, and Rails makes it easy.
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Q
How does Ruby on Rails use the Model View Controller (MVC) framework?
A
Web development can often be divided into three separate but closely integrated subsystems:
Model (Active Record): The model handles all the data logic of the application. In Rails, this is handled by the Active Record library, which forms the bridge between the Ruby program code and the relational database.
View (Action View): The view is the part of the application that the end user sees. In Rails, this is implemented by the Action View library, which is based on Embedded Ruby (ERB) and determines how data will be presented.
Controller (Action Controller): The controller is like the data broker of an application, handling the logic that allows the model and view to communicate with one another. This is called the Action Controller in Rails.
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Q
What is the purpose of the rakefile available in the demo directory in Ruby?
A
The purpose of this simple question is to make sure a developer is familiar with a test-driven development. A beginner may not have dealt with this file yet. The rakefile is similar to the makefile in Unix, and assists with packaging and testing Rails code. It’s used by the rake utility, which ships natively with the Ruby installation.
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Q
Explain the role of the subdirectories app/controllers and app/helpers in Rails.
A
The app/controllers subdirectory holds all the controller classes for the app. Controllers handle web requests from the user. The app/helpers subdirectory holds helper classes, which are used to assist the model, view, and controller classes. By keeping helper classes in a separate subdirectory, the model, view, and controller classes can remain lean and uncluttered.
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Q
How does Rails implement AJAX?
A
Asynchronous JavaScript and XML (AJAX) is a suite of technologies used to retrieve data for a webpage without having to refresh the page itself. This is how modern websites are able to cultivate a “desktop-like” user experience. The Rails method of implementing AJAX operations is short and simple.
First, a trigger is fired. The trigger can be something as simple as a user clicking on a call to action.
Next, the web client uses JavaScript to send data via an XMLHttpRequest from the trigger to an action handler on the server.
On the server-side, a Rails controller action receives the data and returns the corresponding HTML fragment to the client.
The client receives the fragment and updates the view accordingly.
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Q
What is a Rails Migration? Write up a short example of a simple Rails Migration with a table called customers, a string column called name, and a text column called description.
A
Initiating the command c:rubyapplication>ruby script/generate migration table_name will create a Rails Migration. A Rails Migration can be used to create, drop, or remove tables and columns. A potential solution is provided below.
class CreateCustomers < ActiveRecord::Migration
  def up
    create_table :customers do |t|
      t.string :name
      t.text :description
 
      t.timestamps
    end
  end
 
  def down
    drop_table :customers
  end
end
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Q
What is the purpose of the resources method in the code snippet below?
A
resources :posts do
  member do
      get ‘messages’
  end
  collection do
      post ‘bulk_upload'
  end
end
Defining routes with the “resources” method automatically generates routes for the seven standard RESTful actions:
GET /messages
POST /messages
GET /messages/new
GET /messages/:id/edit
GET /messages/:id
PATCH/PUT /messages/:id
DELETE /messages/:id
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Q
Can you explain the difference between ActiveSupport’s “HashWithIndifferentAccess” and Ruby’s “Hash”?
A
The “HashWithIndifferentAccess” class will treat symbol keys and string keys as equivalent while the “Hash” class in Ruby will use the stricter = = comparison on keys—an equivalent string key will not retrieve the value for a given symbol key.
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Q
Explain the role of garbage collection in Ruby on Rails.
A
Garbage collection frees up memory for other processes by removing pointer programs and inaccessible objects left behind after a program has executed. This frees the programmer from having to track objects created dynamically during runtime.
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Q
You’re setting up the routes for a website that displays information on different genres of music. Using the URL path /music/ as an example, create a route that uses a single controller action for each genre of music with the actual music genre passed into the controller action as a parameter. The valid music genres are as follows: classical, rock, house, country, hip_hop, and rnb. All other genres should generate a 404 status code.
A
You will likely receive a variety of potential answers for an open-ended coding question like this, but here are two of the most straightforward approaches to creating a route. The most straightforward solution would be to create a simple route that specifies the controller action to call and passes the genre of music as a parameter. If the genre parameter is not included in the list of valid genres, the action will raise an ActionController::RoutingError and redirect to a 404 page.
get 'music/:genre' => 'music#genre'
Alternatively, a better solution would be to use resource routing which comes with the added benefit of URL generation helpers. You can use the constraints option to verify the validity of a route by checking the parameter against a list of genres. This method requires that the parameter name for the genre be passed as :id and would look something like this:


1) Explain what is Ruby on Rails?

Ruby: It is an object oriented programming language inspired by PERL and PYTHON.
Rails: It is a framework used for building web application
2) Explain what is class libraries in Ruby?

Class libraries in Ruby consist of a variety of domains, such as data types, thread programming, various domains, etc.

3) Mention what is the naming convention in Rails?

Variables: For declaring Variables, all letters are lowercase, and words are separated by underscores
Class and Module: Modules and Classes uses MixedCase and have no underscore; each word starts with a uppercase letter
Database Table: The database table name should have lowercase letters and underscore between words, and all table names should be in the plural form for example invoice_items
Model: It is represented by unbroken MixedCase and always have singular with the table name
Controller: Controller class names are represented in plural form, such that OrdersController would be the controller for the order table.
4) Explain what is “Yield” in Ruby on Rails?

A Ruby method that receives a code block invokes it by calling it with the “Yield”.

5) Explain what is ORM (Object-Relationship-Model) in Rails?

ORM or Object Relationship Model in Rails indicate that your classes are mapped to the table in the database, and objects are directly mapped to the rows in the table.

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6) Mention what the difference is between false and nil in Ruby?

In Ruby False indicates a Boolean datatype, while Nil is not a data type, it have an object_id 4.

7) Mention what are the positive aspects of Rails?

Rails provides many features like

Meta-programming: Rails uses code generation but for heavy lifting it relies on meta-programming. Ruby is considered as one of the best language for Meta-programming.
Active Record: It saves object to the database through Active Record Framework. The Rails version of Active Record identifies the column in a schema and automatically binds them to your domain objects using metaprogramming
Scaffolding: Rails have an ability to create scaffolding or temporary code automatically
Convention over configuration: Unlike other development framework, Rails does not require much configuration, if you follow the naming convention carefully
Three environments: Rails comes with three default environment testing, development, and production.
Built-in-testing: It supports code called harness and fixtures that make test cases to write and execute.
8) Explain what is the role of sub-directory app/controllers and app/helpers?

App/controllers: A web request from the user is handled by the Controller. The controller sub-directory is where Rails looks to find controller classes
App/helpers: The helper’s sub-directory holds any helper classes used to assist the view, model and controller classes.
9) Mention what is the difference between String and Symbol?



They both act in the same way only they differ in their behaviors which are opposite to each other. The difference lies in the object_id, memory and process tune when they are used together. Symbol belongs to the category of immutable objects whereas Strings are considered as mutable objects.

10) Explain how Symbol is different from variables?

Symbol is different from variables in following aspects

It is more like a string than variable
In Ruby string is mutable but a Symbol is immutable
Only one copy of the symbol requires to be created
Symbols are often used as the corresponding to enums in Ruby
11) Explain what is Rails Active Record in Ruby on Rails?

Rails active record is the Object/Relational Mapping (ORM) layer supplied with Rails. It follows the standard ORM model as

Table map to classes
Rows map to objects
Columns map to object attributes
12) Explain how Rails implements Ajax?

Ajax powered web page retrieves the web page from the server which is new or changed unlike other web-page where you have to refresh the page to get the latest information.

Rails triggers an Ajax Operation in following ways

Some trigger fires: The trigger could be a user clicking on a link or button, the users inducing changes to the data in the field or on a form
Web client calls the server: A Java-script method, XMLHttpRequest, sends data linked with the trigger to an action handler on the server. The data might be the ID of a checkbox, the whole form or the text in the entry field
Server does process: The server side action handler does something with the data and retrieves an HTML fragment to the web client
Client receives the response: The client side JavaScript, which Rails generates automatically, receives the HTML fragment and uses it to update a particular part of the current
13) Mention how you can create a controller for subject?

To create a controller for subject you can use the following command

C:\ruby\library> ruby script/generate controller subject

14) Mention what is Rails Migration?

Rails Migration enables Ruby to make changes to the database schema, making it possible to use a version control system to leave things synchronized with the actual code.

15) List out what can Rails Migration do?

Rails Migration can do following things

Create table
Drop table
Rename table
Add column
Rename column
Change column
Remove column and so on
16) Mention what is the command to create a migration?

To create migration command includes

C:\ruby\application>ruby script/generate migration table_name

17) Explain when self.up and self.down method is used?

When migrating to a new version, self.up method is used while self.down method is used to roll back my changes if needed.

18) Mention what is the role of Rails Controller?

The Rails controller is the logical center of the application. It faciliates the interaction between the users, views, and the model. It also performs other activities like

It is capable of routing external requests to internal actions. It handles URL extremely well
It regulates helper modules, which extend the capabilities of the view templates without bulking of their code
It regulates sessions; that gives users the impression of an ongoing interaction with our applications
19) Mention what is the difference between Active support’s “HashWithIndifferent” and Ruby’s “Hash” ?

The Hash class in Ruby’s core library returns value by using a standard “= =” comparison on the keys. It means that the value stored for a symbol key cannot be retrieved using the equivalent string. While the HashWithIndifferentAccess treats Symbol keys and String keys as equivalent.

20) Explain what is Cross-Site Request Forgery (CSRF) and how Rails is protected against it?

CSRF is a form of attack where hacker submits a page request on your behalf to a different website, causing damage or revealing your sensitive data. To protect from CSRF attacks, you have to add “protect_from_forgery” to your ApplicationController. This will cause Rails to require a CSRF token to process the request. CSRF token is given as a hidden field in every form created using Rails form builders.

21) Explain what is Mixin in Rails?

Mixin in Ruby offers an alternative to multiple inheritances, using mixin modules can be imported inside other class.

22) Explain how you define Instance Variable, Global Variable and Class Variable in Ruby?

Ruby Instance variable begins with — @
Ruby Class variables begin with — @@
Ruby Global variables begin with — $
23) Explain how you can run Rails application without creating databases?

You can execute your application by uncommenting the line in environment.rb


path=> rootpath conf/environment.rb

config.frameworks = [ action_web_service, :action_mailer, :active_record]

24) Mention what is the difference between the Observers and Callbacks in Ruby on Rails?

Rails Observers: Observers is same as Callback, but it is used when method is not directly associated to object lifecycle. Also, the observer lives longer, and it can be detached or attached at any time. For example, displaying values from a model in the UI and updating model from user input.
Rails Callback: Callbacks are methods, which can be called at certain moments of an object’s life cycle for example it can be called when an object is validated, created, updated, deleted, A call back is short lived. For example, running a thread and giving a call-back that is called when thread terminates
25) Explain what is rake in Rails?

Rake is a Ruby Make; it is a Ruby utility that substitutes the Unix utility ‘make’, and uses a ‘Rakefile’ and ‘.rake files’ to build up a list of tasks. In Rails, Rake is used for normal administration tasks like migrating the database through scripts, loading a schema into the database, etc.

26) Explain how you can list all routes for an application?

To list out all routes for an application you can write rake routes in the terminal.

27) Explain what is sweeper in Rails?

Sweepers are responsible for expiring or terminating caches when model object changes.

28) Mention the log that has to be seen to report errors in Ruby Rails?

Rails will report errors from Apache in the log/Apache.log and errors from the Ruby code in log/development.log.

29) Explain what is the difference between Dynamic and Static Scaffolding?

Dynamic Scaffolding	Static Scaffolding
It automatically creates the entire content and user interface at runtime
It enables to generation of new, delete, edit methods for the use in application
It does not need a database to be synchronized
It requires manual entry in the command to create the data with their fields
It does not require any such generation to take place
It requires the database to be migrated
30) Mention what is the function of garbage collection in Ruby on Rails?

The functions of garbage collection in Ruby on Rails includes

It enables the removal of the pointer values which is left behind when the execution of the program ends
It frees the programmer from tracking the object that is being created dynamically on runtime
It gives the advantage of removing the inaccessible objects from the memory, and allows other processes to use the memory
31) Mention what is the difference between redirect and render in Ruby on Rails?

Redirect is a method that is used to issue the error message in case the page is not issued or found to the browser. It tells browser to process and issue a new request.
Render is a method used to make the content. Render only works when the controller is being set up properly with the variables that require to be rendered.
32) Mention what is the purpose of RJs in Rails?

RJs is a template that produces JavaScript which is run in an eval block by the browser in response to an AJAX request. It is sometimes used to define the JavaScript, Prototype and helpers provided by Rails.

33) Explain what is Polymorphic Association in Ruby on Rails?

Polymorphic Association allows an ActiveRecord object to be connected with Multiple ActiveRecord objects. A perfect example of Polymorphic Association is a social site where users can comment on anywhere whether it is a videos, photos, link, status updates etc. It would be not feasible if you have to create an individual comment like photos_comments, videos_comment and so on.

34) Mention what are the limits of Ruby on Rails?

Ruby on Rails has been designed for creating a CRUD web application using MVC. This might make Rails not useful for other programmers. Some of the features that Rails does not support include

Foreign key in databases
Linking to multiple data-base at once
Soap web services
Connection to multiple data-base servers at once
35) Mention what is the difference between calling super() and super call?

super(): A call to super() invokes the parent method without any arguments, as presumably expected. As always, being explicit in your code is a good thing.
super call: A call to super invokes the parent method with the same arguments that were passed to the child method. An error will therefore occur if the arguments passed to the child method don’t match what the parent is expecting.
36) Explain about Dig, Float and Max?

Float class is used whenever the function changes constantly.
Dig is used whenever you want to represent a float in decimal digits.
Max is used whenever there is a huge need of Float.
37) Explain how can we define Ruby regular expressions?

Ruby regular expression is a special sequence of characters that helps you match or find other strings. A regular expression literal is a pattern between arbitrary delimiters or slashes followed by %r.

38) Explain what is the defined operator?

Define operator states whether a passed expression is defined or not. If the expression is defined, it returns the description string and if it is not defined it returns a null value.

39) List out the few features of Ruby?

Free format – You can start writing from program from any line and column
Case sensitive – The uppercase and lowercase letters are distinct
Comments – Anything followed by an unquoted #, to the end of the line on which it appears, is ignored by the interpreter
Statement delimiters- Multiple statements on one line must be separated by semicolons, but they are not required at the end of a line.
40) Mention the types of variables available in Ruby Class?

Types of variables available in Ruby Class are,

Local Variables
Global Variables
Class Variables
Instance Variables
41) Explain how can you declare a block in Ruby?

In Ruby, the code in the block is always enclosed within braces ({}).  You can invoke a block by using “yield statement”.

42) Explain what is the difference between put and putc statement?

Unlike the puts statement, which outputs the entire string onto the screen. The Putc statement can be used to output one character at a time.

43) Explain what is a class library in Ruby?

Ruby class libraries consist of a variety of domains, such as thread programming, data types, various domains, etc. These classes give flexible capabilities at a high level of abstraction, giving you the ability to create powerful Ruby scripts useful in a variety of problem domains. The following domains which have relevant class libraries are,

GUI programming
Network programming
CGI Programming
Text processing
44) In Ruby, it explains about the defined operator?

The defined operator tells whether a passed expression is defined or not.  If the expression is not defined, it gives null, and if the expression is defined it returns the description string.

45) Mention what is the difference in scope for these two variables: @@name and @name?

The difference in scope for these two variables is that:

@@name is a class variable
@name is an instance variable
46) Mention what is the syntax for Ruby collect Iterator?

The syntax for Ruby collect Iterator collection = collection.collect.

47) In Ruby code, often it is observed that coder uses a short hand form of using an expression like array.map(&:method_name) instead of array.map { |element| element.method_name }. How this trick actually works?

When a parameter is passed with “&” in front of it. Ruby will call to_proc on it in an attempt to make it usable as a block.  So, symbol to_Proc will invoke the method of the corresponding name on whatever is passed to it. Thus helping our shorthand trick to work.

48) Explain what is Interpolation in Ruby?

Ruby Interpolation is the process of inserting a string into a literal.  By placing a Hash (#) within {} open and close brackets, one can interpolate a string into the literal.

49) Mention what is the Notation used for denoting class variables in Ruby?

In Ruby,

A constant should begin with an uppercase letter, and it should not be defined inside a method
A local must begin with the _ underscore sign or a lowercase letter
A global variable should begin with the $ sign. An uninitialized global has the value of “nil” and it should raise a warning. It can be referred anywhere in the program.
A class variable should begin with double @@ and have to be first initialized before being used in a method definition
50) Mention what is the difference between Procs and Blocks?

The difference between Procs and Blocks,

Block is just the part of the syntax of a method while proc has the characteristics of a block
Procs are objects, blocks are not
At most one block can appear in an argument list
Only block is not able to be stored into a variable while Proc can
51) Mention what is the difference between a single quote and double quote?

A single-quoted strings don’t process ASCII escape codes, and they don’t do string interpolation.

51) Mention what is the difference between a gem and a plugin in Ruby?

Gem: A gem is a just ruby code. It is installed on a machine, and it’s available for all ruby applications running on that machine.
Plugin: Plugin is also ruby code, but it is installed in the application folder and only available for that specific application.
53) Mention what is the difference extend and include?

The “include” makes the module’s methods available to the instance of a class, while “extend” makes these methods available to the class itself.

https://www.toptal.com/ruby/interview-questions
1
What will val1 and val2 equal after the code below is executed? Explain your answer.

val1 = true and false  # hint: output of this statement in IRB is NOT value of val1!
val2 = true && false
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Although these two statements might appear to be equivalent, they are not, due to the order of operations. Specifically, the and and or operators have lower precedence than the = operator, whereas the && and || operators have higher precedence than the = operator, based on order of operations.

To help clarify this, here’s the same code, but employing parentheses to clarify the default order of operations:

(val1 = true) and false    # results in val1 being equal to true
val2 = (true && false)     # results in val2 being equal to false
This is, incidentally, a great example of why using parentheses to clearly specify your intent is generally a good practice, in any language. But whether or not you use parentheses, it’s important to be aware of these order of operations rules and to thereby ensure that you are properly determining when to employ and / or vs. && / ||.
2
Which of the expressions listed below will result in "false"?

true    ? "true" : "false"
false   ? "true" : "false"
nil     ? "true" : "false"
1       ? "true" : "false"
0       ? "true" : "false"
"false" ? "true" : "false"
""      ? "true" : "false"
[]      ? "true" : "false"
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In Ruby, the only values that evaluate to false are false and nil. Everything else – even zero (0) and an empty array ([]) – evaluates to true.

This comes as a real surprise to programmers who have previously been working in other languages like JavaScript.
3
Write a function that sorts the keys in a hash by the length of the key as a string. For instance, the hash:

{ abc: 'hello', 'another_key' => 123, 4567 => 'third' }
should result in:

["abc", "4567", "another_key"]
Hide answer
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As is always true in programming, there are in fact multiple ways to accomplish this.

The most straightforward answer would be of the form:

hsh.keys.map(&:to_s).sort_by(&:length)
or:

hsh.keys.collect(&:to_s).sort_by { |key| key.length }
Alternatively, Ruby’s Enumerable mixin provides many methods to operate on collections. The key here is to turn the hash keys into a collection, convert them all to strings, then sort the array.

def key_sort hsh
	hsh.keys.collect(&:to_s).sort { |a, b| a.length <=> b.length }
end
An equivalent call of the collect method is done with the usual block syntax of:

collect { |x| x.to_s }

......
continuted.
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