Here’s a rather detailed list of Ruby on Rails questions and answers. Hope you find them useful.
This is a very open ended question and you might be better of to start with the basics first:
- A gem is nothing more than a piece of ruby code packaged as a library so that it can be imported and used by others in their programs.
- A Ruby gem is therefore simply a library that is written in the ruby programming language.
- You can add that you often look for ruby gems on rubygems.org. If you have downloaded any recent gems it might be a good idea to mention those. Some of the popular Ruby gems that your interviewer will likely be faimilar with are:
- Finally Rubygems is the name of the project that wrote the “gem” ruby library. [You need not mention this during the interview]
Symbols and string are used interchangeably by various developers and their usage within gems can be confusing at times. You can think of Symbols as faster & immutable strings.
Once a string is used up it is marked for cleaning by the garbage collector but it is not cleaned up immediately and it cannot be reused.
Symbols live for the duration of the session. You might say that this leads to increased memory usage however by keeping the symbol alive a bit longer it can be reused again.
Notice that the object_id stays the same when symbols are created. This happens because the ruby interpreter uses the same heap memory location each time. The symbol was never completely released.
However, in the case of strings the memory is marked for cleanup each time and a new memory is allocated.
Another big difference is that strings can be modified. They are mutable.
The interpreter essentially invokes a separate piece of code and places it in the location. You might say it is similar to a method calling another method. Let’s understand a little bit of background about where yield might be useful first.
The Rails framework encourages you to write code that is DRY (Don’t Repeat Yourself).
Developers often write common code in a central file and then they write the custom code in the specific files. Let’s say you are building a web application and you want all pages to have a common header, a common footer, the same “Welcome user-name!” message.
You can put all this common code in your application.html.erb file.
The rest of the custom code can go in your specific file. Say the page you are creating is the list of articles. Then in your implementation file you would just write the code for pulling in the articles and the final page displayed to the user would be your custom code which will be placed instead of the <%= yield %> code in the application.html.erb file.
Class variables are created using the @@ prefix to denote the variable as class level.
It works just like any other variable, however in the case of inheritance it works more like a static variable that is accessed across all variable instances.
This may appear strange at first, but really all it shows is that the variable my_var is shared across both object instances.
Instance variables are defined using single @ symbol.
Next you can query an object instance to find which instance variables it has.
In the above case we did not put the @ symbol before the instance variables but it is implied.
Global variables are defined using single $ symbol.
Generally you shouldn’t declare too many global variables but sometimes it makes sense to do so. One nice feature of a global variable is that it can be used to trigger a procedure if it’s value changes.
This set the tracking and the procedure is called whenever the value of $foo changes.
Constructors are supported in Ruby. They are declared as the method initialize, shown below. The initialize method gets called automatically when Album.new is called.
where name is the method’s name given as a Symbol, and body is its body given as a Proc, Method, UnboundMethod, or block literal. This allows methods to be defined at runtime, in contrast to def which requires the method name and body to appear literally in the source code.
Module#define_method is a private method so must be called from within the class the method is being defined on. Alternatively, it can be invoked inside class_eval like so:
Kernel#define_singleton_method is called with the same arguments as Module#define_method to define a singleton method on the receiver.
Range is a great way to declare continuous variables. You should use it to declare arrays and other types of collections.
You can also create strings in this format and it fills in the interim values automatically.
Since the end result of using range is an array you can also iterate over it just like any other array.
range2.each do |str|
puts "In Loop #{str}"
end
This produces the result as shown below:
In Loop bar
In Loop bas
In Loop bat
How can you implement method overloading?
This one’s a tricky question. If you have a background in Java then you must know that method overloading is simply multiple methods with same name but different signatures/parameters.
In the case of Ruby method overloading is not supported.
However, it does support the overall goal of passing variable number of parameters to the same method. You would implement it like this:
class MyClass
def initialize(*args)
if args.size < 2 || args.size > 3
puts 'This method takes either 2 or 3 arguments'
else
if args.size == 2
puts 'Found two arguments'
else
puts 'Found three arguments'
end
end
end
end
The output can be seen here:
MyClass.new([10, 23], 4, 10)
Found three arguments
MyClass.new([10, 23], [14, 13])
Found two arguments
SO: You can get the same effect as method overloading but you just have to manage the number of variables inside your method itself.
What is the difference between ‘&&’, ‘and’ and ‘&’ operators?
The ‘&&’ and ‘and’ are both logical and statements. They ‘&&’ operator has higher precedence though. Here’s an example of illustrate this in more detail:
foo = 3
bar = nil
a = foo and bar
# => nil
a
# => 3
a = foo && bar
# => nil
a
# => nil
Notice how the statement ‘a = foo and bar’ actually behaves like ‘(a = foo) and bar’
How can you create setter and getter methods in Ruby?
The setter and getter methods can be created manually by the developer or it can be auto-generated by Ruby using the attr_accessor method specifier.
class Animal
attr_accessor :name, :age
end
anim = Animal.new
=> #<Animal:0x007f8ea20841d8>
anim.age = 3
=> 3
anim.name = "Steve"
=> "Steve"
puts anim.name, anim.age
Steve
3
Of course you can achieve the same result by implementing all the setter and getter methods like this as well:
class Animal
def name # this is the getter method
@name
end
def name=(name) # this is the setter method
@name = name
end
#...same for age...
end
What is the convention for using ‘!’ at the end of a method name?
The ! indicates that the method is about to change the object itself.
Here’s an example:
foo = "A TEST STRING" # a string called foo
foo.downcase! # modifies foo permanently
a test string
puts foo # prints modified foo
a test string
Similarly if you did not want the object to be changed you could have something simple like:
foo2 = "A 2nd Test String" # a string called foo
foo2.downcase # modifies foo temporarily
a 2nd test string
puts foo2 nbsp; # prints original foo
A 2nd Test String
What is a module?
A module is like a class. Except that it can’t be instantiated or subclassed.
In OOP paradigm you would store methods & variables that represent variables in a single class. Say you want to create an Employee representation then the employee’s name, age, salary, etc. would all go inside a Employee class, in a file called Employee.rb
Any methods that act on those variables would also go inside that class.
You can achieve the same effect by putting all the variables and methods inside a Employee module:
module Employee
..variables.
...methods
end
The main difference between the class & module is that a module cannot be instantiated or subclassed.
Module are better suited for library type classes such as Math library, etc.
Does Ruby support multiple inheritance?
Ruby does not support multiple inheritance.
How can you achieve the same effect as multiple inheritance using Ruby? What is mixin?
Ruby offers a very neat alternative concept called mixin. Modules can be imported inside other class using mixin. They are then mixed-in with the class in which they are imported.
Here’s an example:
module Debug
def whoAmI?
"I am #{self.to_s}"
end
end
class Photo
include Debug
end
ph = Photo.new
"I am : #<Photo:0x007f8ea218b270>"
As you can see above the class Debug and it’s method “whoamI?” were mixed-in (added) with the class Photo.
That’s why you can now create an instance of the Photo class and call the whoAmI? method.
ph.whoAmI?
=> "I am : #<Phonograph:0x007f8ea218b270>"
How will you implement a singleton pattern?
Singleton means single instance.
So, the goal of a singleton pattern is to write a class definition but only allow the creation of the single instance of that object.
This can be achieved nicely with the singleton gem as shown below:
require 'singleton'
class Logger
include Singleton
def initialize
@log = File.open("logfile.txt", "a")
end
def log(msg)
@log.puts(msg)
end
end
Adding the singleton as a mixin to the
Logger.instance.log('This is just a test message')
The code above will create a single instance of Logger and simply put the message in the logger file.
Singleton patterns are mostly used for DB instance, Logger instance, etc. —- cases where there should be ONE and only ONE instance of the object that is used.
Sometimes you might like to actually hold on to the logger object and use it everywhere you can do so by the following command:
logObj = Logger.instance
Notice you cannot use the Logger.new to create an object instance because this is a singleton object and therefore calling ‘new’ would fail.
How will you implement an observer pattern?
Let’s review first what an observer pattern is all about.
The observer pattern (sometimes known as publish/subscribe) is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is mainly used to implement distributed event handling systems.
You might have used them in other programming languages as listener objects. You use them whenever a button is clicked on the screen and a method gets called automatically.
As in the case of the singleton pattern, the observer pattern is also implemented by mixing in a module.
In the Ruby implementation, the notifying class mixes in the Observable module, which provides the methods for managing the associated observer objects.
And, the observers must implement the update method to receive notifications.
Here’s an example. Say you want to send an SMS alert to users if a company stock drops then you can do something like this:
require "observer"
require "observer"
class Ticker # Periodically fetch a stock price
include Observable
attr_accessor :price
def initialize symbol, price
@symbol = symbol
@price = price
end
def run
lastPrice = nil
loop do
@price = @price+Random.rand(11)
print "Current price: #{price}\n"
if @price != lastPrice
changed # notify observers
lastPrice = @price
notify_observers(Time.now, @price)
end
end
end
end
class Warner
def initialize ticker
ticker.add_observer(self) # all warners are observers
end
end
class SMSAlert < Warner
def update time, price # callback for observer
print "--- #{time.to_s}: SMS Alert for price: #{price}\n"
end
end
class EmailAlert < Warner
def update time, price # callback for observer
print "+++ #{time.to_s}: Email Alert Price changed to #{price}\n"
end
end
Now let’s initialize the classes and run them:
ticker = Ticker.new("MSFT", 307)
SMSAlert.new(ticker)
EmailAlert.new(ticker)
ticker.run
Current price: 312
--- 2012-02-22 01:26:04 -0800: SMS Alert for price: 312
+++ 2012-02-22 01:26:04 -0800: Email Alert Price changed to 312
Current price: 321
--- 2012-02-22 01:26:04 -0800: SMS Alert for price: 321
+++ 2012-02-22 01:26:04 -0800: Email Alert Price changed to 321
Current price: 323
--- 2012-02-22 01:26:04 -0800: SMS Alert for price: 323
+++ 2012-02-22 01:26:04 -0800: Email Alert Price changed to 323
Current price: 329
--- 2012-02-22 01:26:04 -0800: SMS Alert for price: 329
+++ 2012-02-22 01:26:04 -0800: Email Alert Price changed to 329
What is the purpose of environment.rb and application.rb file?
There are two files where variables and configuration settings are stored.
- config/environment.rb : Environment settings go here
- config/application.rb : Application level global settings go here
config.time_zone = 'Central Time (US & Canada)'
config.i18n.default_locale = :de
config.filter_parameters += [:password] # ensures that passwords are not logged
The same file is also used for configuring various environment settings such as:
config.action_mailer.smtp_settings # various email settings go here
What is the purpose of config/environments/development.rb file?
You would specify various config settings the development environment in this file.
config.action_controller.perform_caching = false # to enable caching
This is because you typically do not want to enable caching in the development environment.
The same config setting in the production environment would be equal to true.
How can you define a constant?
Create a new file as shown below under: config/initializers/my_constants.rb
COLORS = ['white', 'red', 'green']
How can you define a custom Exception?
How can you fire a method when a module is included inside a class?
Fire a method inside a class is very simple.
Say you have a module file trig.rb:
module Trig
PI = 3.141592654
def Trig.sin(x)
# ..
end
def Trig.cos(x)
# ..
end
end
Now you simply import this module inside your class and invoke the method using the “module.method_name” syntax as shown below
require "trig"
class myclass
y = Trig.sin(Trig::PI/4)
This type of invocation ensures that the right module method gets called.
What is the default access modifier (public/protected/private) for a method?
By default all methods are public, except the initialize(constructor) method.
You can make methods private using this declaration within your class:
class MyClass
def method_public_here
end
private# all methods that follow will be made private: not accessible for outside objects
def method_private_here
end
end
How can you call the base class method from inside of its overridden method?
If you are inside the overridden method in the derived class then a simple call to super will call the right method in the base class
class Parent
def try_this()
puts "parent"
end
end
class Child < Parent
def try_this()
super()
puts "child"
end
end
ch = Child.new
ch.try_this()
This generates the output
parent
child
Now if you just want to call the base class without calling the derived class then the best way to do that is to simply assign an alias to the parent method like this:
class Parent
def knox
puts 'parent'
end
end
class Child < Parent
alias_method :parent_knox, :knox
def knox
puts 'child'
end
end
ch = Child.new
ch.parent_knox
ch.knox
This allows you to call the base class method with the alias parent_knox and the derived class method knox can be called directly.
parent
child
Rails Specific Questions
Define the Rails MVC implementation using an example.
What is scope? (or named_scope in Rails 2.x).
Scopes are nothing more than SQL scope fragments. By using these fragments one can cut down on having to write long queries each time you access content.
Say you typically access content as shown below:
@posts = Post.where("published_at IS NOT NULL AND posts.published_at <= "+ Time.now)
Ruby offers you a nice way to put the where condition inside a scope statement as shown below.
class Post < ActiveRecord::Base
scope :published, lambda {
{ :conditions =>
["posts.published_at IS NOT NULL AND posts.published_at <= ?", Time.now]
}
}
scope :recent, :order => "posts.published_at DESC"
end
Now you can simply access the published posts as: Post.published
@posts = Post.published
Also, you can access recent posts as
@recent_posts = Post.recent
Can you give an example of a class that should be inside the lib folder?
Modules are often placed in the lib folder.
Where should you put code that is supposed to run when your application launches?
In the rare event that your application needs to run some code before Rails itself is loaded, put it above the call to require ‘rails/all’ in config/application.rb.
What deployment tool do you use?
Capistrano is a popular deployment tool.
How can you migrate your database schema one level down?
The rake tool does most of the migrations.
It has this nifty syntax to go back one step:
rake db:rollback
If you want to rollback all the way to the beginning you would use:
rake db:reset
This would drop the database, recreate the Database and load the current schema into it
If you want to rollback multiple steps at the same time you would use:
rake db:rollback STEP=3
To rollback all the way and if you are not worried about losing the data then you can drop the database completely with purge like this:
rake db:purge
What is a sweeper?
Sometimes you want to have control over how often and when the cache expires.
Sometimes it is a good idea to have the system determine that on a logical basis. Say you have a list of product on your site and you want to reload the cache each time a new product is added/updated/deleted, then you can achieve this by using the sweeper.
class ProductSweeper < ActionController::Caching::Sweeper
observe Product# This sweeper is going to keep an eye on the Product model
# If our sweeper detects that a Product was created call this
def after_create(product)
expire_cache_for(product)
end
# If our sweeper detects that a Product was updated call this
def after_update(product)
expire_cache_for(product)
end
# If our sweeper detects that a Product was deleted call this
def after_destroy(product)
expire_cache_for(product)
end
private
def expire_cache_for(product)
# Expire the index page now that we added a new product
expire_page(:controller => 'products', :action => 'index')
# Expire a fragment
expire_fragment('all_available_products')
end
end
How can you implement caching in Rails?
Rails offers multiple ways to cache content.
Fragment caching is my favorite because it gives you the choice to fragment to pull a portion from the cache and the remaining from a real-time DB call.
Say you wanted to show all the orders placed on your website in real time and didn’t want to cache that part of the page, but did want to cache the part of the page which lists all products available, you could use this piece of code:
<% Order.find_recent.each do |o| %>
<%= o.buyer.name %> bought <%= o.product.name %>
<% end %>
<% cache do %> All available products:
<% Product.all.each do |p| %>
<%= link_to p.name, product_url(p) %>
<% end %>
<% end %>
Another technique that works well for static pages is page caching. This technique is often used for home pages and is super fast.
class ProductsController < ActionController
caches_page:index
def index
@products = Products.all
end
end
What is a filter? When it is called?
Filters are methods that are called either before/after a controller action is called.
Say a user requests a controller action such as userdashboard/index
In such a case a filter can be setup so that the UserDashboard/index page is only accessible to loggedin users by adding the following lines towards the beginning of the page:
class UserDashboardController < ApplicationController
before_filter :confirm_logged_in, :except => [:login, :attempt_login, :logout]
def index
......
end
After filters are not used too much but they have the effect of executing some code after a particular action has completed. You can use them like triggers.
What do controllers do in Rails?
Once a request comes into the Rails stack, it goes to the routes table to determine which controller and action should be called.
Once a controller action is determined the request is routed to the controller and it does the needed processing by connecting with the DB if needed and then it sends control to the View to render the output.
So, really the flow for Rails goes somewhat like this:
Customer-> Routes-> Controller -> Model(DB) -> Controller -> View -> Customer
How can you divide your controllers into separate modules?
What is RESTful routing?
Routing is fun. If you have ever dealt with IIS you will fall in love with RESTful routing. Here’s how it works.
Say you want your users to have access to certain pages such as:
/photos/new
/photos/1/edit
/photos/1
And, you want the right controller to get called.
And, you want the right view to get rendered.
All this is made possible with a single entry in the routes.rb file as shown below:
resources :photos
In Rails, a resourceful route provides a mapping between HTTP verbs and URLs to controller actions. By convention, each action also maps to particular CRUD operations in a database. The single entry in the routing file creates seven different routes in your application, all mapping to the Photos controller:
How can you list all routes for an application?
rake routes -- will display all routes for an application.
How can you send a multi-part email?
Nowadays most email clients support HTML email, however there are still some old Blackberry phones that prefer emails the ‘ol text way.
Therefore it is important to send emails both as HTML and text. This technique is called multi-part emails.
The ActionMailer class (included in Rails 3.0) does a great job of sending both text and HTML emails out to the end user at the same time.
By default Rails sending an email with plain/text content_type, for example:
# app/models/notifier.rb
def send_email(email)
subject email.subject
from email.from
recipients email.recipients
sent_on Time.now
body :email => email
end
Next let’s update the view in : app/views/notifier/send_email.html.erb
Welcome to here:
The sent email is a plain text email
Date: Thu, 5 Aug 2010 16:38:07 +0800
From: RailsBP
To: flyerhzm@gmail.com
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Welcome: http://rails-bestpractices.com
The link url is just displayed as a plain text because of the email content_type.
text/html
If we want the email clients to display link url as html format, we should change the content_type to text/html in the app/models/notifier.rb file
def send_email(email)
subject email.subject
from email.from
recipients email.recipients
sent_on Time.now
content_type "text/html"
body :email => email
end
Now the sent email is a html formatted email
Date: Thu, 5 Aug 2010 17:32:27 +0800
From: RailsBP
To: flyerhzm@gmail.com
Mime-Version: 1.0
Content-Type: text/html; charset=utf-8
Welcome: http://rails-bestpractices.com
Now the email client can display the link url correctly with html format.
The email header looks somewhat like this:
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_002C_01BFABBF.4A7D6BA0"
Content-Type: multipart/alternative tells the e-mail program to expect different parts to follow, separated by a boundary which specified in quotation marks. Actually the boundary could be anything, though hyphens, equal signs, and underscores insure that the e-mail program won't try to display this boundary to the recipient.
------=_NextPart_000_002C_01BFABBF.4A7D6BA0
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: 8bit
What is the purpose of layouts?
Layouts are partial ruby/html files that are used to render the content pages.
There are placed in the folder: app/views/layouts
Items that you would typically put in this folder are things like headers/footers, navigation elements, etc.
Here’s a sample layout file: /app/views/layout/application.html.erb
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Learning System | <%= @page_title || 'Admin Area' %></title>
<meta name="author" content="Anil Punjabi">
<%= stylesheet_link_tag('public', 'admin', :media => 'all') %>
<%= javascript_include_tag('application') %>
</head>
<body>
<div id="header">
<h1>Learning System</h1>
</div>
<div id="main">
<% if !flash[:notice].blank? %>
<div class="notice">
<%= flash[:notice] %>
</div>
<% end %>
<div id="content">
<%= yield %>
</div>
</div>
<div id="footer">
<p id="copyright">© / Anil Punjabi</p>
</div>
</body>
</html>
Say you are trying to access the page as shown below:
Then the contents of the index.html.erb would be placed above in the section shown under <% yield %> above and sent back to the user.
Is it possible to embed partial views inside layouts? How?
That is the purpose of layouts. You embed partial views inside the file /app/views/layout/application.html.erb and then whenever you render any page this layout is merged with it.
What is the purpose of RJS?
How can you create a REST API for your application?
How can you define a new environment called ‘staging’?
What is Rake?
Rake is a popular ruby gem that makes the job of running tasks simpler.
Rake is most often used for DB tasks, but it can be used for m
The common DB commands are:
rake db:migrate
rake db:reset
You can use cron to schedule rake tasks.
Sometimes you would create a dataloader.rake file and put it in the lib/tasks folder so that it can be used to populate the database on startup.
What is Capistrano?
Capistrano is a popular deployment tool — it allows developers to push code from their desktop to the servers.
What is a polymorophic association?
How can you implement a polymorphic association?
What is a has and belongs to many association?
What is the difference between has_one and belongs_to?
How can you implement single table inheritance?
What is eager loading?
Eager loading is a great optimization strategy to reduce the number of queries that are made against the DB.
Say you are finding 10 employees and then you are looking for their post codes. Then your query would appear something like this:
clients = Client.limit(10)
clients.each do |client|
puts client.address.postcode
end
This may seem fine at first look but really this implementation leaves much to be desired. It makes 11 DB calls just to get the results.
Now you can optimize this query by making a slight change in the request like this:
clients = Client.includes(:address).limit(10)
clients.each do |client|
puts client.address.postcode
end
This new request makes two SQL calls like this:
SELECT * FROM clients LIMIT 10
SELECT addresses.* FROM addresses
WHERE (addresses.client_id IN (1,2,3,4,5,6,7,8,9,10))
So, as you can see it really loads a lot more upfront and therefore it is called eager loading.
How can you eager load associated objects?
How does validation work?
Validation means checking to see if data is good before it is stored in the database.
During signups and other such user input cases you want to check and be sure that the data is validated. In the past developers would often put this type of validation logic as triggers in the database.
In an MVC architecture one can do validations at each level.
You can do validations in the controllers but it is usually a good idea to keep your controllers skinny.
Views suffer from the javascript limitation because javascript can be disabled on the client side so they are not completely reliable.
The best way to manage validation is to put it in the model code. This model code is really the closest as you can be to the database and works very well for Rails applications.
Here are a few validation examples:
class Person < ActiveRecord::Base
validates :name, :length => { :minimum => 2 }
validates :points, :numericality => { :only_integer => true } # only integer
validates :age, :numericality => { :greater_than => 18 } # greater than 18
validates :email, :uniqueness => true
validates :email, :confirmation => true # this is to validate that the two email fields are identical
validates :email_confirmation, :presence => true # this is to validate that the email confirmation field is not nil
In your view template you may use something like this:
<%= text_field :person, :email %> <%= text_field :person, :email_confirmation %>
How can you add a custom validation on your model?
Now custom validations takes it to the next step.
Say you want to confirm that the data meets certain criteria
How can you implement a custom theme for your forms?
Why is fields_for used for?
What is the purpose of a helper method?
What is flash?
Flash is simply a way to pass some value to the next action.
Anything you place in the flash will be exposed to the very next action and then cleared out.
Here’s an example:
def destroy section = Section.find(params[:id]) section.destroy flash[:notice] = "Section destroyed." redirect_to(:action => 'list', :page_id => @page.id) end
Then wherever you want to use the flash you can write this code. I often put this snippet in the application.html.erb file, somewhere towards the top:
<% if !flash[:notice].blank? %> <div class="notice"> <%= flash[:notice] %>
How can you install the missing gems that are required by your application in the simplest way?
bundle install
This command will install all dependencies and missing gems. It looks at your Gemfile to figure out what gems are needed by your application.
How can you implement internationalization?
Ruby ships with i18n which is an internationalization gem.
You need to create locale files and save them under the config/locales directory as:
en.yml
es.yml
fr.yml
The keys should match for each of these files.
en: main_page: hello: “Hello†welcome: “Welcome to My Company†es: main_page: hello: “Hola†welcome: “Bienvenido a Mi Empresa†fr: main_page: hello: “Salut†welcome: “Bienvenue à Mon Entrepriseâ€
In your code you would need to specify that the text would be locale specific. So change it to something like this:
.content %h1 = t("main_page.hello") %p = t("main_page.welcome") Then you have to select the actual locale, which the users can do from a menu option.
More details here
How can you configure your application for different environments?
How can you instruct rails logger to ignore passwords and such fields while logging?
Test Frameworks
Ruby on Rails has a number of built-in and a few other third-party test frameworks. Here are a few sample questions on such frameworks:
Are you familiar with unit testing?
How does functional testing differ from unit testing?
Have you ever used a mocking framework?
Are you familiar with BDD using RSpec or Cucumber?
What is an alternative to using test fixtures?
How can you reuse part of a text fixture?
How do you specify associations in the test fixture yml files?
Plugins
Plugins are the principal mechanism to reuse code. The open-source community is at full-bloom when it comes about plugins. The Rails Plugins site has a really good list of such plugins from the community.
What plugin would you recommend for user authentication and authorization?
Devise works great with Rails.
It supports OAuth authentication and therefore integrates nicely with Facebook.
What plugin do you use for full-text search?
Sunspot supports full-text search capability and uses Solr as the back-end search engine to do so.
You would include these two plugins in your gem file as shown below:
gem 'sunspot_rails'
gem 'sunspot_solr'
More details here
How can you implement a state machine?
What is the difference between a plugin and a gem?
A gem is just ruby code. It is installed on a machine and it’s available for all ruby applications running on that machine.
Rails, rake, json, rspec — are all examples of gems.
Plugin is also ruby code but it is installed in the application folder and only available for that specific application.
Sitemap-generator, etc.
In general, since Rails works well with gems you will find that you would be mostly integrating with gem files and not plugins in general. Most developers release their libraries as gems.
How can you create a plugin?
You can read about how to create a rails plugin here:
Plugin Guide
How can you implement a search feature that searches for multiple models?
If you are using acts_as_solr for your search you will be able to use multi_solr_search to enable search across multiple models.
Also, you can configure Sunspot/Solr to support search across multiple models. Here’s a post about it
Sphinx, another powerful search server can be used to search across multiple models and it works great.
How can you upload a file to a server?
Paperclip is the best solution to manage file uploads to a server.
It can also help you with multiple file uploads and associate it with ActiveRecord.
There are also good examples online that show how you can make rotating sliders with the paperclip images.
Another nice solution is using carrier_wave gem.
The nice thing about carrier_wave is that it has good documentation on how to integrate with S3, Google & Rackspace for file storage.
You can achieve the same file storage capability with Paperclip as well though.
SEO Related Questions
How can you generate sitemaps for your Rails site?
You can use dynamic_sitemaps gem to generate sitemaps
How can you show search user friendly urls instead of using only numeric ids?
The simplest way to do this is to use the gem FriendlyID.
It gives you the ability to specify a friendly URL for pages so that instead of the standard page URLs like:
http://mysite.com/page/1
You can build pages such as:
http://mysite.com/page/my-awesome-page-about-articles-and-content
How can you create page titles and metadata for your pages?
You can use the Headliner plugin for adding page titles.
You can use the MetaMagic plugin to add meta tags.
How can you create breadcrumbs on your pages?
Gretel is a great plugin to introduce breadcrumbs in your Rails application.
Another very simple implementation is breadcrumb_on_rails.
Architecture Related Questions
This questions can be from different angles like: quality, security, scalability, manageability, interoperability, reusability and all the other ilities you name! Here are a few example questions:
Is Rails scalable?
Yes Rails gives you complete freedom to use all traditional means of scaling an application. Things like memcached, caching full pages, caching fragments are all supported.
You can use any standard CDN to serve your media and static content as well.
Database scaling using sharding is supported.
Finally heroku makes your life easier by giving you the flexibility to scale up/down based on your need. Mostly websites have a peak time during which you need more servers and then there is a sleep time. Heroku makes that on-demand scaling process simpler. Companies such as HireFireApp.com makes the autoscale process easier.
What are the key deployment challenges?
heroku makes deployment easy.
Things that I sometimes run into are:
> Mismatched gem versions between local and production environment
> Some lessons learned:
»» Use image_tag helper each time
»» Specify root path in ENV variable
»» Configure assets pipeline by setting: config.assets.enabled = true in the config/application.rb file
Configure Capistrano script to precompile assets
Here’s a nice video about Assets Pipeline
How can you safeguard a rails application from SQL injection attack?
Rails already has the logic built into it to prevent SQL injection attacks if you follow the right syntax.
Say you are trying to authenticate a user based on their login and password you might be tempted to use a syntax as below:
User.first("login = '#{params[:name]}' AND password = '#{params[:password]}'")
If an attacker enters ’ OR ‘1’=‘1 as the name, and ’ OR ’2’>’1 as the password, the resulting SQL query will be:
SELECT * FROM users WHERE login = '' OR '1'='1' AND password = '' OR '2'>'1' LIMIT 1
This will simply find the first record in the database, and grants access to this user.
To prevent this type of SQL injection simply use the following format.
User.where("login = ? AND password = ?", entered_user_name, entered_password).first
OR
User.where(:login => entered_user_name, :password => entered_password).first
How can you secure a rails application?
Rails has a lot of in-built capabilities to deal with common web-security issues.
> SQL Injection
> Cross-Site
> Session fixation and Session hijacking
> Captcha
Follow this useful security guide
How can rails engage with a SOA platform?
Overall Community Questions
Can you tell me a few good community resources for Rails?
Stackoverflow, Github, various Meetup groups
Where would you reach out to get the community to answer your questions?
Stackoverflow and meetup groups.
Which famous applications are built using ruby on rails?
Basecamp
Shopify
Adventures in Technology & Business Strategy
